pushing the limits of harmonic approaches for the …dctc16.sns.it/poster_dctc16.pdfa comparative...
TRANSCRIPT
Pushing the limits of harmonic approaches for the simulation electronic spectra
Javier Cerezo,1 Fabrizio Santoro1
1Istituto di Chimica dei Composti Organometallici, ICCOM-CNR, Via G. Moruzzi – Pisaj.cerezo @ pi.iccom.cnr .it
During the last years, the availability of efficient electronic structure methods to model excitedstates together with the development of protocols to account for the full electronic lineshapes usingboth time independent (TI) and time-dependent (TD) approaches [1] in the harmonic approximationhave led to methodologies that are nowadays able to provide impressively accurate estimations ofthe spectral shapes. Indeed, in the cases where the harmonic approximation is valid, thesecomputational procedures represent a very useful technique to better understand the experimentalsignatures, allowing to extract more refined information from the spectra, including that about thenuclear rearrangements in the solute and the solvent response.
In this contribution, we review some of the methodologies developed and applied in our groupduring the last years to evaluate the lineshape [2-7], showcasing some interesting realizations,which include the adoption of both Cartesian and valence internal coordinates and differentapproaches to build the potential energy surfaces of the initial and final electronic states, namelyadiabatic and vertical models. We pay especial attention to flexible systems, where the wise choiceof the aforementioned theoretical set-ups allow to push the applicability of the harmonicapproximation or offer a convenient framework to extend the calculation to anharmonic treatments.
References[1] (a) A. Lami and F. Santoro. Time-Dependent Approaches to Calculation of Steady-StateVibronic Spectra: From Fully Quantum to Classical Approaches. In V. Barone, (Ed.), ComputationalStrategies for Spectroscopy: from Small Molecules to Nanosystems, John Wiley & Sons, Inc., 2011,475-516, Chapter 10; (b) M. Biczysko, J. Bloino, F. Santoro and V. Barone, Time-IndependentApproaches to Simulate Electronic Spectra Lineshapes. ibid 361-443, Chapter 8[2] F.J. Avila Ferrer and F. Santoro. Phys. Chem. Chem. Phys., 2012, 14, 13549-13563[3] J. Cerezo, J. Zúñiga, A. Requena, F.J. Avila Ferrer and F. Santoro. J. Chem. Theory Comput.,2013, 9, 4947-4958[4] F.J. Avila Ferrer, J. Cerezo, J. Soto, R. Improta and F. Santoro. Comput. Theoret. Chem., 2014,1040-1041, 328-337[5] J. Cerezo, F.J. Avila Ferrer G. Prampolini and F. Santoro. J. Chem. Theory Comput., 2015, 11,5810-5825[6] J. Cerezo, F. Santoro and G. Prampolini. Theor. Chem. Acc., 2016, 135, 1-21[7] J. Cerezo and F. Santoro. J. Chem. Theory Comput., 2016, doi:10.1021/acs.jctc.6b00442
P1
On the Stability of Helium Compounds: Insights from Charge Displacement Analysis
Francesca Nunzi, 1,2 Diego Cesario,1 Francesco Tarantelli,1,2 Leonardo Belpassi2 1 Department of Chemistry, Biology and Biotechnologies, University of Perugia, via Elce di Sotto 8,
I-06123 Perugia, Italy2 Computational Laboratory of Hybrid/Organic Photovoltaics (CLHYO), CNR-ISTM, via Elce di Sotto 8, I-06123 Perugia, Italy
diego.cesario @studenti.unipg.it
Since the discovery of xenon compound in 2000, the interest for neutral noble gas compounds has grown extensively. Nowadays few noble gas adducts have been observed, containing the heavier noble gases, Ar, Kr and Xe, while no compounds containing lighter He and Ne have been experimentally observed. Even if numerous studies have been devoted to the rationalization of the chemical bond in He and Ne compounds, at present time a comprehensive explanation of the exact nature of the He chemistry and of the higher strength of He vs Ne bond is still missing.
We therefore carried out high level quantum mechanics calculations on Ng compounds with prototypical molecules (BeO, BeCO3 and MF, M=Au, Cu), aiming at clarifying the nature of the interaction of light vs. heavy Ng atoms. A detailed analysis of the chemical bond in these weakly bound complexes has been carried out by employing the Charge Displacement Function,1, 2 a powerful tool for the charge displacement analysis, that allows us to unambiguously identify and quantify the net electron charge flow upon formation of the noble gas - substrate bond along the considered interaction axis.
Our calculations confirm that in the investigated noble gases complexes the bond has a partial covalent character, since a net charge transfer occurs from the noble gas to the interacting substrate. The charge transfer is greater for Xe, and decrease going up in the group, as expected on the basis of the atomic properties. Unexpectedly, for helium compounds, we also found a net charge transfer from the substrate to the helium atom, that further stabilize the interaction. This interaction is peculiar and exclusive of He in the noble gases series and represents a plausible explanation to the unexpected higher strength of He vs Ne complexes in the interaction with strong acceptor partners.
(1) Belpassi, L.; Infante, I.; Tarantelli, F.; Visscher, L. The Chemical Bond Between Au(I) AndThe Noble Gases. Comparative Study Of NgAuF And NgAu+ (Ng = Ar, Kr, Xe) By DensityFunctional And Coupled Cluster Methods. J. Am. Chem. Soc. 2008, 130, 1048-1060.(2) Bistoni, G.; Rampino, S.; Tarantelli, F.; Belpassi, L. Charge-Displacement Analysis ViaNatural Orbitals For Chemical Valence: Charge Transfer Effects In Coordination Chemistry. J.Chem. Phys. 2015, 142, 084112.
P2
Absolute binding free energies of ligand-receptor complexes through nonequilibrium decoupling schemes based on constrained dynamics
Gianni Cardini, Riccardo Chelli, Matteo Cioni,
Edoardo Giovannelli, Emanuele Grifoni, Piero Procacci
Dipartimento di Chimica, Università di Firenze, Via della Lastruccia, 3 – Sesto Fiorentino [email protected]
Assessing absolute binding free energies of ligand-receptor complexes with a chemical accuracy is an important challenge of theoretical and computational chemistry. Methodologies based on molecular dynamics simulations have been important advances in recent years1. One of most widely known approaches is the alchemical double decoupling method2, in which the interactions of the ligand with its surroundings are progressively switched off. For this method, restraining potentials are activated and released during the simulation for sampling efficiently the changes in translational, rotational and conformational freedom of the ligand and receptor upon binding. Because such restraining potentials add bias to the simulations, it is fundamental that their effects be removed to yield a binding free energy that is properly unbiased with respect to the standard state. In the present contribution, we propose two alternative strategies (similar to each other) for double decoupling method, in which the ligand is strongly constrained within the binding site of the receptor, thus avoiding any reweighing procedure for removing the bias. This approach is applied in the framework of an alchemical scheme based on a series of simulations in which the interaction potential involving the ligand is switched off in a continuous way3,4. The binding free energy is estimated exploiting the set of works computed in these simulations by using nonequilibrium work theorems5. Numerical validation is provided by applying the method to a simple complex involving the Zn ion. Another interesting application to complexes of β-cyclodextrine with aromatic compounds is also reported. References
1. C. Chipot, A. Pohorille, Free Energy Calculations: Theory and Applications in Chemistry and Biology, Springer, Berlin, 2007.
2. M. K. Gilson, J. A. Given, B. L. Bush, J. A. McCammon, The statistical-thermodynamic basis for computation of binding affinities: a critical review, Biophys. J. 1997, 72, 1047-1069.
3. P. Procacci, I. Dissociation free energies of drug-receptor systems via non-equilibrium alchemical simulations: a theoretical framework, Phys. Chem. Chem. Phys. 2016, 18, 14991-15004.
4. F. Nerattini, R. Chelli, P. Procacci, II. Dissociation free energies in drug-receptor systems via nonequilibrium alchemical simulations: application to the FK506-related immunophilin ligands, Phys. Chem. Chem. Phys. 2016, 18, 15005-15018.
5. C. Jarzynski, Nonequilibrium equality for free energy differences, Phys. Rev. Lett. 1997, 78, 2690-2693.
P3
Computing Free Energy Differences of Configurational Basins Edoardo Giovannelli,1 Gianni Cardini1,2, Cristina Gellini1,2, Giangaetano Pietraperzia 1,2, Riccardo
Chelli1,2 1 Dipartimento di Chimica, Universita di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino,
Italy 2 European Laboratory for Nonlinear Spectroscopy (LENS), Via Nello Carrara 1, I-50019 Sesto
Fiorentino, Italy [email protected]
A simulation-based approach is proposed to estimate free energy differences between configurational states A and B, defined in terms of collective coordinates of the molecular system. The computational protocol is organized into three stages that can be carried on simultaneously. Two of them consist of independent simulations aimed at sampling, in turn, A and B states. In order to limit the evolution of the system around A and B, biased sampling simulations such as umbrella sampling can be employed. These simulations allow us to estimate local configuration integrals associated with A and B, which can be viewed as vibrational contributions to the free energy. Free energy evaluation is completed by the linking-path stage, in which the potential of mean force difference is estimated between two arbitrary points of the configurational surface, located the first around A and the second around B. The linking path in the space of the collective coordinates is arbitrary and can be computed with any method, starting from adaptive biasing potential/force approaches to nonequilibrium techniques. As an illustrative example, we present the calculation of free energy differences between conformational states of the alanine dipeptide in the space of backbone dihedral angles. The basic advantage of this method, that we term “path-linked domains” scheme, is to prevent accurate calculation of the whole free energy hypersurface in the space of the collective coordinates, thus limiting the statistical sampling to a minimum. Path-linked domains schemes can be applied to a variety of biochemical processes, such as protein−ligand complexation or folding-unfolding interconversion.
P4
Assessment of Different Quantum Mechanical Methods for the Prediction of Structure and Cohesive Energy of
Molecular Crystals Michele Cutini,1 Bartolomeo Civalleri,1,* Marta Corno,1 Roberto Orlando,1
Jan Gerit Brandenburg2, Lorenzo Maschio,1 and Piero Ugliengo1
1University of Turin, Department of Chemistry, Via P. Giuria 7 - Turin, (IT); 2Mulliken Center of Theoretical Chemistry, Institut für Physikalische und
Theoretische Chemie, Universität Bonn, Beringstraße 4 – Bonn (DE) [email protected]
A comparative assessment of the accuracy of different quantum mechanical methods for evaluating the structure and the cohesive energy of molecular crystals is presented. In particular, we evaluate the performance of the semi-empirical HF-3c [1] method in comparison with the B3LYP-D*, [2] and the Local MP2 (LMP2) methods by means of a fully periodic approach.[3] Three benchmark sets have been investigated: X23,[4] G60,[5] and the new K7; for a total of 82 molecular crystals. The original HF-3c method performs well, but shows a tendency at overbinding molecular crystals, in particular for weakly bounded systems. For the X23 set, the mean absolute error for the cohesive energies computed with the HF-3c method is comparable to the LMP2 one. A refinement of the HF-3c has been attempted by tuning the dispersion term in the HF-3c energy. While the performance on cohesive energy prediction slightly worsens, optimized unit cell volumes are in excellent agreement with experiment. Overall, the B3LYP-D* method combined with a TZP basis set gives the best results. For cost-effective calculations on molecular crystals, we propose to compute cohesive energies at the B3LYP-D*/TZP level of theory on the dispersion-scaled HF-3c optimized geometries. References [1] Sure, R.; Grimme, S. J. Comput. Chem. 2013, 34, 1672. [2] Civalleri, B.; Zicovich-Wilson, C. M.; Valenzano, L.; Ugliengo, P. CrystEngComm 2008, 82 (1994), 4. [3] Pisani, C.; Schütz, M.; et al. Phys. Chem. Chem. Phys. 2012, 14, 7615. [4] Reilly, A. M.; Tkatchenko, A. J. Chem. Phys. 2013, 139, 024705. [5] Maschio, L.; Civalleri, B.; et al. J. Phys. Chem. A 2011, 115, 11179.
P5
Computational Investigations on the Structural and Optical Properties of
Fluorophores within a Sunlight Harvesting Device
Gianluca Del Frate,1 Fabio Bellina,2 Giordano Mancini,1 Giulia Marianetti,1 Pierpaolo Minei,2 Andrea Pucci,2 Vincenzo Barone1
1Scuola Normale Superiore, Classe di Scienze, Piazza dei Cavalieri 7, Pisa, Italy
2Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Moruzzi 13, Pisa, Italy [email protected]
In photovoltaic technology, Luminescent Solar Concentrators (LSCs) represent a promising solution in decreasing the cost per unit of power generated [1]. Such systems consist of a trasparent, polymeric sheet doped with appropriate photoactive species able to absorbe sunlight and re-emitting it with high efficiency at red-shifted wavelength. The active species, usually based on extended π-conjugated structures, should be stable from a chemical point of view and exhibit large Stoke shifts, in order to avoid re-absorption losses. Furthermore, their spectral features have to be easily tunable from the visible to the near infrared by only changing the kind of functional groups embedded in the main, aromatic core [2]. Recently [3], the spectroscopic features of a new family of fluorophores were investigated by means of an experimental and theoretical study, in order to evaluate possible applications of such organic compounds as luminescent species in the above mentioned photovoltaic devices. These studies revealed that the quantum yelds of the dyes computed both in a poly(methyl metaacrilate) (PMMA) matrix and in a THF solution assumed the same value, thus suggesting an increased stiffness of the dyes dissolved within the polymer (which compensate for the loss of efficiency usually observed upon dispersion). Here, using Molecular Dynamics (MD) simulations based on purposely tailored force fields [4], we rationalize at the atomistic level the above mentioned experimental observations, confirming the increased rigidity of these organic dyes when going from the liquid solution to the polymeric matrix. Moreover, we evaluate different protocols in the computation of the absorption spectra of the same fluorophores within the polymer embedding. We show that a fast, “static” approach, describing environment effects through the Polarizable Continuum Model (PCM), correctly reproduce the main observed spectroscopic features, so to be confirmed as a useful tool in assisting experiments among the selection of the best candidates as photoactive species in LSCs. References [1] W. G. van Sark, Renewable Energy, 2013, 49, 207-210. [2] F. Bures, RSC Adv., 2014, 4, 58826-58849. [3] V. Barone, F. Bellina, M. Biczysko, J. Bloino, T. Fornaro, C. Latouche, M. Lessi, G. Marianetti, P. Minei, A. Panattoni, A. Pucci, Phys. Chem. Chem. Phys., 2015, 17, 26710-26723. [4] V. Barone, I. Cacelli, N. De Mitri, D. Licari, S. Monti, G. Prampolini, Phys. Chem. Chem.
P6
An experimental and theoretical investigation of 1-butanol pyrolysis
Noelia Faginas-Lago,1 Nadia Balucani1, Domenico Stranges2, Dimitrios Skouteris3, Leonardo Pacifici1, Stefano Falcinelli4, Marzio Rosi4
1Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Via Elce di Sotto, 8 – Perugia; 2Dipartimento di Chimica, Sapienza Università di Roma, Piazzale A. Moro 5 –
Roma; 3Scuola Normale Superiore di Pisa, Piazza dei Cavalieri, 7 – Pisa; 4Dipartimento di Ingegneria Civile ed Ambientale, Università degli Studi di Perugia, Via G. Duranti – Perugia
[email protected] Among bio-alcohols, bio-butanol is considered a very promising biofuel candidate because of its relatively high energy content, low water absorption, high miscibility with conventional fuels, and the possibility of being used in conventional engines.In our laboratory, we have performed a series of experiments based on the flash pyrolysis technique and mass spectrometric detection with the aim to understand thermal decomposition of biofuels at the molecular level[1]. To support the interpretation of the experimental results, electronic structure calculations of the stationary points of the potential energy surface associated with the unimolecular decomposition of 1-butanol have been performed. The new results compare well with those of previous work, but the channels leading to H emission have been characterized for the first time. In addition, RRKM based statistical estimates of the yield of the various fragmentation channels have
been performed. The final purpose is to obtain a convincing description of the micromechanism of 1-butanol unimolecular dissociation. Such a detailed description is necessary to build realistic combustion models where also the minor processes leading to pollutant production in trace amounts need to be understood and, eventually, controlled and mitigated. References [1]L. Pacifici, N. Faginas-Lago, A. Lombardi, N. Balucani, D. Stranges, S. Falcinelli, and M. Rosi “A Theoretical Investigation of 1-
Butanol Unimolecular Decomposition” Lecture Notes in Computer Science (Workshop on Chemistry and Molecular & Materials Sciences and Technologies) Part II, LNCS 9156, 384-393 DOI: 10.1007/978-3-319-21407-8 28 (2015).
P7
The effect of the potential energy surface on vibrational transitions in N2-N2 collisions
S. Fioccola1*, F. Pirani2, M. Bartolomei3 and C. Coletti1
1Dipartimento di Farmacia, Università G. d'Annunzio Chieti-Pescara, Via dei Vestini, 66100 Chieti, Italy.
2Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy
3Instituto de Física Fundamental - CSIC, C/ Serrano 123, Madrid, Spain.
Non equilibrium conditions can be the rule in the chemistry of the upper atmosphere, combustion and laser chemistry, and in the chemistry of plasma, especially when the vibrations of diatomic molecules are concerned. In this sense, vibrationally excited molecules and vibration to vibration (VV) energy transfer in N2-N2 collisions play a crucial role both in high temperature, as in hypersonic flows in the atmosphere, and in low temperature (gas lasers, plasma reactors) regimes, so that the accurate experimental and theoretical determination of cross sections and rate constants of related processes is a topic of increasing interest [1,2,3].
One of the most efficient approaches to calculated these quantities remains at the date the quantum-classical method introduced and developed by Billing [4], which couples a rigorous quantum mechanical treatment of vibrations and of roto-vibrational coupling and a quasiclassical description of the other degrees of freedom, allowing the calculation of energy exchange probabilities for a large body of state selected processes at a reasonable computational cost.
The accuracy of the results thus strongly depends on the ability of the potential energy surfaces to correctly describe both long and short range interactions which dominate the outcome of the collisions at different temperature regimes.
In this work we compare cross sections and rate constants for VV processes in N2-N2 collisions, calculated within a mixed quantum-classical approach in a wide temperature range, using the potential recently adopted in [1], its updated version, obtained by modifying the long range interaction, and the potential energy surface of ref. [3], which includes reactive channels in the description of the interaction.
References
[1] A. Kurnosov, M. Cacciatore, A. Laganà, F. Pirani, M. Bartolomei, E. Garcia, J. Comput. Chem., 35 722 (2014).
[2] R.Z. Martinez, D. Bermejo, Phys. Chem. Chem. Phys., 17 12661 (2015)
[3] J.D. Bender, P. Valentini, I. Nompelis, Y. Paukku, D.G. Truhlar, Z. Varga, T. Scwarzentruber, G.V. Candler, J. Chem. Phys., 143 054304 (2015)
P8
Mechanistic explanation of Acoustic Wave Enhanced Catalysis (AWEC)
– an opportunity for unique catalytic transformations
Alessandro Fortunelli,1 William A. Goddard III2, Luca Sementa1, Giovanni Barcaro1, Fabio R. Negreiros1, Qi An2, Jin Qian2, Robert R. Nielsen2
1CNR-ICCOM, Consiglio Nazionale delle Ricerche, Via G. Moruzzi, 1 – Pisa; 2Dipartimento di Chimica, Sapienza Università di Roma, Piazzale A. Moro 5 – Roma.
Experimental evidence that surface acoustic waves (SAW) can significantly enhance the rate of catalytic oxidation of CO to CO2 over the Pt(110) catalyst surface [1] is examined using quantum mechanics (QM) simulations. First we determined the QM based mechanism for the O2-rich régime of the reaction, and the energy landscape of CO interacting with an oxygen-covered reconstructed Pt(110) surface at both static and dynamic levels, but in the absence of SAW. We then utilized ab initio molecular dynamic (AIMD) simulations to determine how SAW might modify the kinetics. We focus here on the short (picosecond time scale) shock spikes induced by switching of domains in the piezoelectric driver on which the catalyst is deposited. We find that SAW-induced spikes promote dynamic changes in the diffusion and desorption, from which we estimate the influence of SAW on CO oxidation rate over Pt(110). We find good agreement with the experimentally observed catalytic enhancement by SAW. With an atomistic mechanism in place one can now consider how to use SAW to enhance other catalytic reactions. References [1] S. Kelling et al., Faraday Disc., 1997, 107, 435–444 [2] Qi An, Jin Qian, Robert R. Nielsen, Luca Sementa, Giovanni Barcaro, Fabio R. Negreiros, Alessandro Fortunelli, William A. Goddard III, J. Mater. Chem. A, 2016, 4, 12036-12045, DOI: 10.1039/C6TA03669D
P9
Core-level spectroscopic study of derivatives of phenyl-boronic acid on Au(111) surface: an experimental and theoretical investigation.
Giovanna Fronzoni1, Daniele Toffoli1, Hande Ustunel2, Mauro Stener,1 Albano Cossaro 3, Carlo Dri 3, Zhijing Feng 3,4d
1 Department of Chemical and Pharmaceutical Sciences, University of Trieste, Trieste, Italy 2 Department of Physics, Middle East Technical University, Ankara, Turkey
3 CNR-IOM Laboratorio Nazionale TASC, Trieste, Italy 4 Department of Physics, University of Trieste, , Trieste, Italy
The controlled formation of boron-based 2D and ultrathin films of covalent organic frameworks (COFs) as nano-templates or for device applications is a major topic of research in surface science [1-3]. In this work we investigate the B1s and O1s NEXAFS (near-edge X-ray absorption fine structure) of condensed phase of the phenyl-boronic acid deposited on Au(111) surface, by both experiments and DFT (density functional theory) calculations. The inspection of the experimental STM (Scanning Tunneling Spectroscopy) images reveals that the triphenylboroxine (TPB) is the predominant oligomer on the Au surface at low temperature. Guided by the experimental STM images, we considered three different adsorption models for TPB on the Au(111) surface and optimized them by a periodic slab methodology. In a second step suitable finite clusters were cut from the periodic relaxed structures and used for the calculation of the O1s and B1s NEXAFS spectra of the adsorbed molecule. Despite the overall qualitative good agreement between theory and experiments concerning the gross features of NEXAFS spectra for both O1s and B1s excitations, we find that the ability of DFT to describe the most intense core level excitations deteriorates when the core hole is localized on Boron compared to Oxygen. This aspect is currently under study on a series of derivatives of boronic acid in the gas phase.
References
1. S. Clair, M. Abel, L. Porte, ChemComm, 2014, 50, 9627 2. R. Nishiyabu, Y. Kubo, T. D. James, J. S. Fossey, ChemComm, 2011, 47, 1077 3. N. A. A. Zwaneveld, R. Pawlak, M. Abel, D. Catalin, D. Gigmes, D. Bertin, L. Porte, JACS, 2008, 130, 6678
P10
Simulation of accurate vibrationally resolved phosphorescence spectra
Marco Fusè, Alberto Baiardi, Vincenzo Barone
Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy [email protected]
Triplet emitters, in the figure of organometallic complexes, have attracted considerable attention in the last years due to their applicability in electroluminescent devices such as OLEDs, sensors and probes. In these systems, the formally spin-forbidden transition between the triplet and the singlet ground states is allowed by the presence of large spin-orbit coupling (SOC). Electronic spectroscopy is the most powerful tool to investigate these chemical systems, and a proper interpretation of the experimental spectra increasingly relies on theoretical methodologies. For these organometallic systems, usually with more than 50-100 atoms, computational methods rooted in DFT and its time dependent extension (TD-DFT) are particularly appealing due to their computational efficiency. However, the simulations of electronic spectra are usually performed either neglecting or treating in an approximate way the effects of molecular vibrations (usually referred to as vibronic effects). This limits significantly the reliability of the simulations, since a proper account of vibronic effects is mandatory to get a realistic reproduction of experimental band-shapes, which are usually asymmetric also for low-resolution spectra. In our group, a general tool for the simulation of different kinds of one-photon spectroscopies has been developed. This tool, based on the harmonic approximation of both the potential energy surfaces (PESs) involved in the transition, supports different vibronic models both in internal and in cartesian coordinates [1] with the possible inclusion of mode-mixing and Herzberg-Teller (HT) effects [2,3]. In this contribution, this tool has been extended to support also phosphorescence spectroscopies (both the standard emission and its chiral counterpart, also known as circularly polarized phosphorescence, CPP) at the same level of approximation. Dealing with the simulation of phosphorescence spectra, the main issue concerns the computation of the electronic transition moments (both electric and magnetic, for chiroptical spectroscopy) and their derivatives (for the HT case). Here, these quantities have been calculated in a non-relativistic framework within perturbation theory, following a recently proposed protocol [4]. In practice, computations have been performed using a locally modified version of the DALTON package. In order to improve the computational efficiency of the simulations, the two-electron part of the SO operator has been approximated by either the effective charge (HEC) or the atomic mean-field (MNF) model within the velocity gauge formalism. Then, the obtained values have been used into a locally modified version of the GAUSSIAN suite of programs to compute the vibronic spectra. Three simple and experimentally well-characterized organic molecules (benzophenone, (1R,4R)-bycyclo[2.2.1]hept-5-en-2-one and camphorquinone) have been used as test-cases to check the reliability of the vibronic models by comparing the theoretical results with the available experimental data, both for phosphorescence and for CPP. The aim of the simulations has been to determine a computational protocol representing the best compromise between accuracy and computational effort, with the final goal of applying it to larger-size systems such as metal complexes. References [1] A. Baiardi, J. Bloino, V. Barone, J. Chem. Phys. 2016, 144, 84114. [2] V. Barone, A. Baiardi, J. Bloino, in Chirality, 2014, pp. 588–600. [3] J. Bloino, A. Baiardi, M. Biczysko, Int. J. Quantum Chem. 2016, DOI 10.1002/qua.25188. [4] M. Kamiński, J. Cukras, M. Pecul, A. Rizzo, S. Coriani, Phys. Chem. Chem. Phys. 2015, 17, 19079–19086.
P11
The VMS-Draw Tool: What's New
Daniele Licari1
1Scuola Normale Superiore, piazza dei Cavalieri 7, I-56126 Pisa, Italy [email protected]
In a previous work (Licari et al., 2014), the VMS-Draw tool was presented for the analysis of spectroscopic data produced by computer simulations. It has had a significant improvement since then in performance, features, usability and robustness. This poster will present the latest release of VMS Draw. It allows the analysis of complete spectral shapes for infrared (IR), vibrational circular dichroism (VCD), nonresonance Raman and resonance Raman, Raman optical activity (ROA) and resonance Raman optical activity (RROA), electronic one-photon absorption (OPA) and one-photon emission (OPE), electronic circular dichroism (ECD), and circularly polarized luminescence (CPL). The simulations of these type of spectroscopy are performed by our algorithms implemented in Gaussian 09 package. Some recent developments regarding computational tools were required in order to extend VMS Draw with new spectroscopies. In the case of NMR spectroscopy, the specific module (written in FORTRAN90/95 language) has been developed, compiled for different operating systems (Windows, Mac-OS and Linux based systems) and included in the VMS-Draw package as stand-alone executable. The new tool guides the user in the input creation process, simulation and data analysis of the results. VMS-Draw provides facilities for drawing, comparing and modifying the computed spectra. It has a short and gradual learning curve, allowing the novice user to quickly obtain useful results. In the Rotational spectroscopy, VMS Draw provides a suite of tools able to fitting, simulate and analyze a microwave spectrum starting from a specific Gaussian 09 Output file and interfacing with the SPCAT/SPFIT Tools binary (Pickett,1991). In addition, a new assignments tool able to compare the experimental spectrum with the prediction one and assign lines accordingly was developed. The assigned spectral lines are used by SPFIT program to calculate a new set of parameters which are used into an iterative refinement process to improve the accuracy of numerical simulation. References [Licari et al.,2014] Licari, D.; Baiardi, A.; Biczysko, M.; Egidi, F.; Latouche, C; Barone, V.; Implementation of graphical user interface for the virtual multifrequency spectrometer: the VMS-Draw tool; Manuscript JCC, 2014. [Frisch et al.,2009] Gaussian 09, Revision E.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2009. [Pickett,1991] H.M.Pickett, J.Mol.Spectrosc. 148,371-377, 1991.
P12
Ligand-field strength and covalency in Cu(II) complexes: a combined experimental and theoretical study
G. Mangione,1 M. Casarin1
1Università degli Studi di Padova, Dipartimento di Scienze Chimiche, Via F. Marzolo 1, 35131 Padova, Italy
[email protected] X-ray absorption spectroscopy (XAS) is as a powerful tool able to provide a chemically selective probe of the unoccupied electronic structure of molecular systems. XAS features are generated by excitations from the core levels of the absorbing atom to the frontier unoccupied orbitals as well as to the continuum; thus making this technique very sensitive to both the electronic structure and the local surroundings of the absorbing species. Transition Metal (M) L2,3-edges features are generated by the electric-dipole allowed 2pMgndM excitations, providing insight into the participation of ndM AOs in the low-lying unoccupied MOs. In general, both the simulation and the analysis of L2,3 spectra of M complexes are challenging issues. As such, Cu(II) complexes represent the simplest possible case study[1] because electric-dipole allowed 2pCu(II)g3dCu(II) transitions generate a 2p53d10 final configuration. The corresponding spectral pattern is dominated by the 2p spin-orbit (SO) coupling, while both the energetics and the spectral feature intensities are mainly influenced by ligand-field strength and covalency, respectively.[2] Solomon and co-workers[2] proposed an empirical model exploiting the normalized intensities and the relative positions of CuL2,3 features in different Cu(II) complexes as a gauge of the Cu(II)–ligand covalency and of the ligand-field strength, respectively. The larger is the L3 normalized intensity, the lower is the metal–ligand covalency; the higher is the L3 excitation energy, the stronger is the ligand-field exerted on the Cu(II) centre. The Cu(II) L2,3 spectra of different Cu(II) complexes have been modelled by means of time-dependent density functional theory (TDDFT) calculations within the Tamm–Dancoff approximation (TDA) coupled to the relativistic zeroth-order regular approximation (ZORA) including SO effects. The analysis of the composition of the L3-edge excitations revealed that, in addition to 2pCu(II)g3dCu(II) excitations, metal-to-ligand charge-transfer transitions (involving low-lying ligand-based π* MOs) contribute to its intensity thereby weakening its believed relationship with the M–ligand covalency. References
1. a) F. de Groot, Coord. Chem. Rev. 2005, 249, 31-63; b) F. de Groot, A. Kotani, Core Level Spectroscopy of Solids, CRC Press, Boca Raton, 2008.
2. a) S. J. George, M. D. Lowery, E. I. Solomon, S. P. Cramer, J. Am. Chem. Soc. 1993, 115, 2968–2969; b) R. K. Hocking, E. I. Solomon, Struct. Bonding (Berlin) 2012, 142, 155–184.
P13
Sc3+ in aqueous solution: the strange case of the far-coordinated water molecule
Valentina Migliorati, Paola D'Angelo
Dipartimento di Chimica, Sapienza Università di Roma, Piazzale A. Moro 5 – Roma. [email protected]
The chemical and industrial applications of scandium compounds have increased considerably in recent years.[1,2] As an example, Sc3+ trifluoromethanesulfonate (triflate) is an efficient recyclable Lewis acid able to catalyze many important types of organic reactions, and its catalytic activity is in several cases significantly higher than that of the lanthanoid(III) triflates. Knowledge of Sc3+coordination properties is of great importance, and even if much theoretical and experimental work has been devoted to unravel the Sc3+ hydration,[3-5] the results are surprisingly widespread, lacking a unified picture for the solvation of this ion in aqueous solution. In particular, coordination numbers comprised between 6 and 8 have been reported in the literature, and also the geometry of the Sc3+ hydration complex is still the subject of intense debate.[3-5] Here, we will show how the combined use of Quantum-Mechanical (QM) calculations, classical Molecular Dynamics (MD) simulations, and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy allowed us to shed light into the peculiar coordination properties of this ion in water. In particular, QM calculations have been adopted to generate an effective Sc-water two-body potential to be used in the MD simulation of Sc3+ in water, and the reliability of the theoretical procedure has been assessed by comparing the theoretical structural results with the EXAFS experimental data. The interesting result of this combined study is that the Sc3+ ion forms a well-defined capped square antiprism (SAP) complex in aqueous solution, where the eight water molecules closest to the ion are located at the vertexes of a SAP polyhedron, while the ninth water molecule occupying the capping position is unusually found at a very long distance from the ion. This far-coordinated water molecule possesses a degree of structuring comparable with the other first shell molecules surrounding the ion at much shorter distances, and its presence gave us the unique opportunity to easily identify the geometry of the Sc3+ coordination polyhedron. Moreover, the Sc3+ hydration shell has been found to be very labile, as the far-coordinated ligand allows first shell water molecules to easily exchange their positions both inside the solvation shell and with the rest of the solvent molecules. The structural and dynamic properties of the Sc3+ aqua ion found could explain the high catalitic activity of Sc3+ compounds when used as Lewis acids for catalysing many types of organic reactions. Indeed, the flexible nature of the Sc3+ coordination cluster could increase the accessibility of the ligands to the ion, and therefore the ion effectiveness as a Lewis acid. References [1] L. Zhu, Y. Liu, J. Chen, W. Liu J. Appl. Polym. Sci. 2011, 120, 3284. [2] B. Onghena, K. Binnemans Ind. Eng. Chem. Res. 2015, 54, 1887. [3] W.W. Rudolph, C.C. Pye J. Phys. Chem. A 2000, 104, 1627. [4] A. Abbasi, P. Lindqvist-Reis, L. Eriksson, D. Sandström, S. Lidin, I. Persson, M. Sandström Chem. Eur. J. 2005, 11, 4065. [5] P. Lindqvist-Reis, I. Persson, M. Sandström Dalton Trans. 2006, 3868.
P14
Palygoskite and Sepiolite as traps and storages for Carbon Dioxide
Federica Lodesani, Francesco Muniz-Miranda, Davide Presti, Francesco Tavanti, Daniele
Malferrari, Alfonso Pedone Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, Via G.
campi 103, Modena [email protected]
Carbon dioxide is a product of both biological and current energy-production processes. This latter aspect attracts a great deal of interest since CO2 is a greenhouse gas, and the increase of its emissions nowadays is often connected by environmental scientists to the so-called “global warming”1 and ocean acidification.2 As a consequence, the possibility to capture and entrap CO2, thus taking it away from the lower atmosphere, is often viewed as a feasible way to counter the global temperature increase.3 Therefore, the possibility to store CO2 in subsurface geological strata attracts scientific, technological and political interest. Much of the recent literature has been devoted to studying Montmorillonite;4 however, there are other minerals with inner cavities/channels suitable to host mixtures of H2O/CO2, such as Sepiolite and Palygorskite. These two clays are phyllosilicates with octahedrically coordinated Si4
+ and a different ratio of Al3+ and Mg2+, along with large channels of different sizes where a certain quantity of water molecules are naturally present. So, these clays are promising candidates for the capture and storage of carbon dioxide. It order to monitor the behavior of CO2 in these clays it is important to understand their interplay, and here the molecular dynamics approach represents a necessary tool to study their interaction. In this oral presentation it is shown how carbon dioxide, water, clays, and potassium impurities interact with each other.
Sepiolite Palygorskite References (1) Le Quéré, C. et al. Earth System Science Data 2015, 7, 349–396. (2) Caldeira, K.; Wickett, M. E. Nature 2003, 365. (3) Carbon Storage: www.netl.doe.gov/technologies/carbon_seq/corerd/storage.html (4) Myshakin, E. M.; Saidi, W. A.; Romanov, V. N.; Cygan, R. T.; Jordan, K. D. The Journal of Physical Chemistry C 2013, 117, 11028–11039.
P15
A fully polarizable QM/MM/PCM Approach to Modeling Vibrational Circular Dichroism and Raman Optical Activity Spectra
Marta Olszówka , 1 Tommaso Giovannini 2 , Chiara Cappelli 2
1 Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Moruzzi 13 – Pisa; 2 Scuola Normale Superiore, Piazza dei Cavalieri 7 Pisa.
The vast and still growing availability of QM methods for the calculation of molecular response to an external field allows for the theoretical study of a great number of spectroscopic properties, including the interaction between the chiral molecules and polarized light. In the present research we propose a methodology to calculate the Vibrational Circular Dichroism [1] and Raman Optical Activity spectra using a fully polarizable Quantum Mechanical (QM)/Molecular Mechanics (MM)/Polarizable Continuum Model (PCM) Hamiltonian. The framework hereby proposed enables the calculations of the spectra of systems in solution which is particularly important due to the fact that the experimental spectra are usually recorded for such conditions. Contrary to the standard QM/MM approaches [2], this one includes polarization effects in the MM force field by means of Fluctuating Charges (FQ) [35]. In further details, the computations of VCD spectra require the implementation of the first and second derivatives and magnetic response properties with GIAOs [68]. Meanwhile, the ROA requires also the third derivatives of energy with respect to electric and magnetic field [9]. The working equations for both these spectroscopies are presented. The importance of an accurate description of environmental effects for chiroptical properties has already been proven and discussed [10]. References [1] Polavarapu, P. L. Chem. Rec. 2007, 7, 125136 [2] A. Warshel, M. Levitt, J. Mol. Biol. 1976, 103, 227249 [3] F. Lipparini, V. Barone, J. Chem. Theory Comput. 2011, 7, 37113724 [4] F. Lipparini, C. Cappelli, V. Barone, J. Chem. Theory Comput. 2012, 8, 41534165 [5] C. Cappelli, Int. J. Quantum Chem. 2016 [6] T. Giovannini, M. Olszówka, C. Cappelli, submitted [7] F. Lipparini, C. Cappelli, V. Barone. J. Chem. Phys., 2013, 138, 234108 [8] F. Lipparini, C. Cappelli, G. Scalmani, N. De Mitri, V. Barone. J. Chem. Theory Comput. 2012, 8, 42704278 [9] T. Giovannini, M. Olszówka, C. Cappelli, in preparation [10] F. Lipparini, F. Egidi, C. Cappelli, V. Barone, J. Chem. Theory Comput. 2013, 9, 18801884 ,
P16
Modeling Excited State Proton Transfer to solvent:
a dynamics study of a super photoacid with an hybrid implicit/explicit solvent model
Umberto Raucci,1 Nadia Rega1,2
1Department of Chemical Sciences, University Federico II of Napoli, Napoli, Italy; 2 Italian Institute of Technology, IIT@CRIB Center for Advanced Biomaterials for Healthcare
Napoli, Italy [email protected]
The classification of organic molecules according to their acidity is a fundamental topic of every introductive chemistry course. Nevertheless, it can be completely overturned at the excited electronic state. In few words, the electronic redistribution occurring in some molecules upon light irradiation can drastically affect the acidity of the protonated site, which in turn dissociates transferring a proton to a nearby solvent molecule or to a strong base present in solution.[1] The understanding of Excited State Proton Transfer (ESPT) reactivity is very difficult to obtain at molecular level. Indeed, a wide range of time scales affects the ESPT kinetics, going from the femtosecond (electron density redistribution of the chromophore) to the nanosecond (diffusion process after the reaction) scale.[1] Furthermore the reaction phase space is very complex, involving both the photoacid and solvent degrees of freedom.[1,2] The exploration of different time scales in a very complex reaction space represents the main challenge for the theoretical simulation of ESPT processes. What is more, theoretical approaches are called to handle at the same time both the electronic redistribution of the chromophore and the solvent relaxation around the proton transferring complex, finely modulating the kinetics and thermodynamics of the reaction. In this contribution we took up this challenge, investigating the mechanism and driving forces of ESPT reactions by means of Time-Dependent Density Functional Theory (TD-DFT) based ab-initio molecular dynamics (AIMD) simulations by adopting different solvation models and schemes to represent the environmental effects. At the basic level, implicit solvent model allows to follow the formation of the proton transfer adduct catching the features of the electronic rearrangement which drives the reaction.[3] Nevertheless to achieve the full exploration of the product region during the simulation an explicit solvent representation is mandatory. Hybrid implicit/explicit model of solvation represents an appealing choice to consider in an explicit way the solvent coordinate in the ESPT toward water solvent molecules. Different QM/MM partitions were examined revealing that the explicit and polarizable representation of both the first and the second shell around the proton acceptor molecule is necessary to stabilize the hydronium ion. Moreover their low frequency modes assist and modulate the overall process. In general we demonstrated that AIMD based on TD-DFT and robust solvent models appears to be a feasible and reliable way to represent both the electronical, nuclear and solute/solvent rearrangement ruling photo-triggered processes in condensed phase. References [1]. Simkovitch R., Shomer S., Gepshtein R., Huppert D., J. Phys. Chem. B, 2014, 119, 2253, 6
[2]. Cimino P., Raucci U., Donati G., Chiariello M.G., Rega N., Theor. Chem. Acc., 2016, 135, 117 [3]. Raucci U., Savarese M., Adamo C., Ciofini I., Rega N., J. Phys. Chem. B, 2015, 119, 2650, 6 [4]. Brancato G., Rega N., Barone V., J. Chem. Phys., 2008, 128, 144501, 14
P17
Modifying the Reactivity of Zirconia via Nanostructuring: A DFT+U Study of Au Atom Adsorption and H2 Dissociation
Antonio Ruiz, Gianfranco Pacchioni
Dipartimento di Scienza dei Materiali, Università degli Studi di Milano – Bicocca, Via R. Cozzi 55 – Milano
The reactivity of zirconia (ZrO2) has been investigated by means of DFT+U calculations as a function of morphology and stoichiometry, and considering two cases: the adsorption of a Au atom and the dissociation of H2. We show that, under stoichiometric conditions, 1 – 2 nm nanoparticles lead to enhanced Au binding energies and redox processes in the ZrO2 – Au interface that are not found in the extended surfaces (regular or stepped). Under reducing conditions, nanostructuring plays an opposite role: nanoparticles stabilize O vacancies, becoming then less reactive systems toward Au adsorption.1 An opposite reactivity upon nanostructuring has also been observed in the H2 dissociation. The heterolytic splitting (formation of Zr-H– and O-H+ bonds) is the preferred mechanism on the extended surfaces. Instead, on nanoparticles the dissociation goes through a homolytic (reductive) dissociation, where two O-H+ bonds and two Zr3+ centers are formed.2 In this respect, nanostructuring may have dramatic effects on the reactivity of ZrO2 toward H2 and modify the catalytic activity of the deposited metals, which is due to a higher structural flexibility and special electronic structure.3 References [1] A. Ruiz Puigdollers, F. Illas, G. Pacchioni. Effect of Nanostructuring on the Reactivity of Zirconia: A DFT+U Study of Au Atom Adsorption. J. Phys. Chem. C 2016, 120, 17604. [2] A. Ruiz Puigdollers, S. Tosoni, G. Pacchioni. Turning a Nonreducible into a Reducible Oxide via Nanostructuring: Opposite Behavior of Bulk ZrO2 and ZrO2 Nanoparticles Toward H2 Adsorption. J. Phys. Chem. C 2016, 120, 15329. [3] A. Ruiz Puigdollers, F. Illas, G. Pacchioni. Structure and Properties of Zirconia Nanoparticles from Density Functional Theory Calculations. J. Phys. Chem. C 2016, 120, 4392.
P18
Theoretical Quantification of the Modified Photoactivity of Photochromes Grafted on Metallic Nanoparticles
Roberto Russo,1 Arnaud Fihey2, Benedetta Mennucci1, Denis Jacquemin2
1Dipartimento di Chimica, Università di Pisa, Via Moruzzi, 13 – Pisa; 2Dipartimento di Chimica, Sapienza Università di Roma, Piazzale A. Moro 5 – Roma.
We present a quantum-mechanical study of the photoactivity of nanoscale architectures based on dithienylethene (DTE) photochromic molecules grafted onto plasmonic gold or silver nanoparticles. The effects of the metal NPs are included in each step of the QM description through a Polarizable Continuum Model [1]. Using this QM/PCM methodology [2], we here investigate the influence of the LSPR of NPs on the optical properties of different DTEs, and show that theoretical tools provide access to accurate spectroscopic data explaining the experimental outcomes for systems in which the metallic part is covered with a photochromic coat (a typical example is given in the figure below). By a direct comparison with measured data, we demonstrate that such a multiscale model is able to provide a reliable quantification of the spectroscopic parameters characterizing the photoactivity of the switches as well as their evolution under the influence of the plasmonic effects. In particular, both the calculated enhancement factors describing the enhancement of the DTE photoreactivity close to the NP[3,4] and the calculated cyclization/cycloreversion quantum yields accounting for the efficiency of the photochromism, [5] are in close agreement with the experimental data. In addition, a better understanding of the photo-induced behavior of such complex nanoscaled photochromic systems is given in terms of a molecular-level description.
References [1] Tomasi, J.; Mennucci, B.; Cammi, R., Chem. Rev. 2005, 105, 2999–3094.
[2] Vukovic, S.; Corni, S.; Mennucci, B., J. Phys. Chem. C 2009, 113, 121–133
[3] Nishi, H.; Asahi, T.; Kobatake, S., ChemPhysChem 2012, 13, 3616–3621
[4] Nishi, H.; Asahi, T.; Kobatake, S., J. Phys. Chem. C 2011, 115, 4564–4570.
[5] Yamaguchi, H.; Matsuda, K.; Irie, M., J. Phys. Chem. C 2007, 111, 3853–3862.
P19
An “under the hood” look at the Caffeine molecular viewer
Andrea Salvadori, Giordano Mancini
Scuola Normale Superiore, Piazza dei Cavalieri 7, Pisa, Italy; [email protected]
Caffeine is a new molecular viewer developed at the SMART Laboratory of Scuola Normale Superiore (SNS) specifically designed to exploit modern Immersive Virtual Reality (IVR) technologies. Caffeine supports both standard desktop computers as well as IVR systems such as the CAVE theater installed at SNS. The latest features of the program have been presented in a recent work published on the International Journal of Quantum Chemistry [1]. The study also discuss the main advantages general users can expect from the ongoing integration of conventional methods of computational chemistry with advanced IVR technologies by presenting some case studies. The proposed poster presents Caffeine from a technological point of view, discussing some modern real-time computer graphics techniques employed by Caffeine and other recent molecular viewers in order to visualize large assemblies and related properties at high frame-rates and good visual quality. Finally, a performance comparison between Caffeine and some other popular molecular graphical systems is presented. References [1] Salvadori, A., Del Frate, G., Pagliai, M., Mancini, G. and Barone, V., “Immersive virtual reality in computational chemistry: Applications to the analysis of QM and MM data”, International Journal of Quantum Chemistry, 2016, DOI:10.1002/qua.25207
P20
Computational investigations on the unexpected extrusion of molecular iodine in Pd(II) σ-butadienyl complexes.
Thomas Scattolina, Fabiano Visentina, Luciano Canovesea and Claudio Santoa
aDipartimento di Scienze Molecolari e Nanosistemi, Universita` Ca’ Foscari, Venezia e-mail: [email protected]
We have experimentally and theoretically studied the stoichiometric addition of halogens or interhalogens to σ-butadienyl Pd(II) complexes bearing thioquinolines as spectator ligands.1 The observed reactions do not involve the expected elimination of the butadienyl fragment2 but rather the unpredictable extrusion of molecular iodine (Schemes 1-2).1
NSPdE
E E
EI
IBr or IClBr(Cl)
NSPdE
E E
EI
I I2
E = COOMe
CH2Cl2, R.T., 10'
1a 1b-1c
NSPdE
E E
EBr
Br2Br
NSPdE
E E
EI
I I2
E = COOMe
CH2Cl2, R.T., 24 h
1a 2a
Scheme 1 Scheme 2 We have explained this peculiar reactivity with a mechanistic hypothesis (Scheme 3) involving Pd(IV) intermediates (to save computer time, the COOMe was substituted with CN group).1
In the case of the reaction between complex 1a and IBr, it is apparent from the computational output (Scheme 4) that I2 and complex 1b represent the favored reaction products from both kinetic and thermodynamic points of view (the energy values are expressed as ΔG° at 298K).
Scheme 3 Scheme 4 The geometrical optimization of the complexes was carried out using the hyper-GGA functional MO6 3 in combination with the LAN2TZ(f) 4 basis set for the Pd atoms, the LANL2DZdp basis set5 for the halogen atoms and the 6-31G(d,p) basis set for the other elements. Solvent effects (dichloromethane, ε =8.93) were included using CPCM6. The thermodynamic parameters were obtained by means of the stationary points characterized by IR simulation. References 1. T.Scattolin, F.Visentin, C.Santo, V.Bertolasi, L.Canovese, Dalton Trans., 2016, 45, 11560-11567 2. R.V.Belzen, C.J.Elsevier, A.Dedieu, N.Veldman, A.L.Spek, Organometallics, 2003, 22, 722-736 3. Y.Zhao, D.G.Truhlar, Theor. Chem. Acc., 2008, 120, 215-241 4. L.E.Roy, P.J.Hay, R.L.Martin, J. Chem. Theory Comput., 2008, 4, 1029-1031 5. C.E.Check, T.Faust, J.M.Bailey, B.J.Wright, T.Gilbert, J. Phys. Chem. A, 2001, 105, 8111- 8116 6. V.Barone, M.Cossi, J.Tomasi, J. Chem. Phys. 1997, 107, 3210-3221
P21
CO oxidation on Au nanoparticles supported on TiO2 anatase (101):
A Mars-van Krevelen mechanism?
Philomena Schlexer1, Gianfranco Pacchioni1
1Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Via R. Cozzi, 5 – 20125 Milano [email protected]
CO oxidation is the major solution to CO abatement in air depollution treatments. State of the art catalysts are monoliths coated with Pt-group metals. The production of these catalysts is expensive and higher temperatures (>200 °C) are needed for the catalyst activation. Gold nanoparticles supported on titania (TiO2) show great catalytic activity for CO oxidation even at room temperature. To improve the low-temperature activity of commercial catalytic converters, it is necessary to gain a fundamental understanding of the working principles of low-temperature catalysts. Mechanistic investigations of CO oxidation on titania-supported Au catalyst have been subject to experimental and theoretical studies in the past, but so far no consensus on the reaction mechanism has been established. In a recent experimental study, J. Behm et al. investigated the oxidation of CO involving the TiO2 lattice oxygen in the presence of Au nanoparticles. [1] Based on their findings, we performed spin-polarized periodic DFT+U calculations including vdW-forces to investigate the reaction pathway. To model the Au nanoparticles, we designed periodic Au nano-rods supported on the TiO2 anatase (101) surface. Detailed energy profiles of the reaction steps including transition states were calculated, which allow us to propose a complete catalytic cycle of CO oxidation via the Mars-van Krevelen mechanism. References [1] D. Widmann, A. Krautsieder, P. Walter, A. Bruckner, R. J. Behm, ACS Catal. 6 (2016) 5005
P22
Ab initio investigation of polyethylene glycol (PEG) coating of TiO2 surfaces
Daniele Selli,1 Cristiana di Valentin1
1Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, via Cozzi 55 20125, Milano, Italy
In biomedical applications, TiO2 nanoparticles are generally coated with polymers to prevent agglomeration, improve biocompatibility and reduce their cytotoxicity [1]. Although the synthesis processes of such composite compounds are well established [2], there is still a big lack of information on the nature of the interaction between the titania surface and the organic macromolecules. In this work, the adsorption of polyethylene glycol (PEG) on the TiO2 (101) anatase surface is modeled by means of dispersion-corrected density functional theory (DFT-D2) calculations [3]. The two extreme limits of an infinite PEG polymer [−(O−CH2−CH2)n], on one side, and of a short PEG dimer molecule [H−(O−CH2−CH2)2−OH], on the other, are analyzed. Many different molecular configurations and modes of adsorption are compared, at increasing surface coverage densities. At low and medium coverage, PEG prefers to lay down on the surface, while at full coverage, the adsorption is maximized when PEG molecules bind perpendicularly to the surface and interact with each other through lateral dispersions, following a mushroom to brush transition [4]. Finally, we also consider the adsorption of competing water molecules at different coverage densities, assessing whether PEG would remain bonded to the surface or desorb in the presence of the aqueous solvent. References [1] S.S. Mano, K. Kanehira, S. Sonezaki, A. Taniguchi, Int J Mol Sci 13 (2012) 3703-3717. [2] J.V. Jokerst, T. Lobovkin, R.N. Zare, S.S. Gambhir, Nanomedicine 6 (2011) 715–728. [3] S. Grimme, J. Comput. Chem. 27 (2006) 1787-1799. [4] N. Backmann, N. Kappeler, T. Braun, F. Huber, H.-P. Lang, C. Gerber, R.Y.H. Lim, Beilstein J Nanotechnol. 1 (2010) 3–13.
P23
A computational study on the optical interaction between BODIPY and the
[Au25(SCH3)18]- cluster: long-range interactions
Mauro Stener,1 Paolo Ronchese1, Giovanna Fronzoni1, Daniele Toffoli1, Alessandro Fortunelli2, Luca Sementa2, Giovanni Barcaro2
1Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Via L. Giorgieri 1 - Trieste; 2CNR-ICCOM, Consiglio Nazionale delle Ricerche
via Giuseppe Moruzzi 1, 56124, Pisa. [email protected]
BODIPY (boron-dipyrromethene) is the forefather of a class of fluorescent dyes which have attracted much attention due to its very high quantum yield. In this study we have considered the effect on the BODIPY absorption spectrum in the presence of the [Au25(SCH3)18]- metal cluster. The two systems have been considered in three different mutual orientations, in order to have the dipole transition density of the BODIPY pointing towards or away from the cluster. The cluster has an icosahedral metal core, its structure is almost spherical therefore only BODIPY orientation is important to assess the interaction. When the mutual orientation favors the maximum interaction, long-range effects have been found, which tend to suppress the intensity of the BODIPY absorption transitions up to distances of more than 20Å. Two different structures of the metal clusters have been considered, and the interaction has been found strongly dependent by the cluster structure.
P24
Entangled polyethylene modeling at ab-initio level
Vincenzo Villani1, Gaetano Giammarino1, Vito Lavallata1 and Nicola Pugno2
1Università della Basilicata, Dipartimento di Scienze, Campus Macchia Romana, Potenza; 2Laboratory of Bio-Inspired & Graphene Nanomechanis, Department of Civil, Environmental and
Mechanical Engineering, Università di Trento, via Mesiano, 77, Trento. [email protected]
In the recent past, one of us developed1 a simple yet efficient way to exceptionally improve the tenacity of a polymer fiber, introducing a slip-knot as a frictional element along the fiber under stretching. In this way, when tensioned, the fiber moves through the loop dissipating elasticity energy via friction: for high-modulus polyethylene, fracture energy has been found to raise from 44 J/g to 1070 J/g. At macromolecular level, for a long and flexible chain the presence of entanglements and knots is an entropically favoured configuration2. Therefore, it is well known the presence of topological constraints in proteins, nucleic acids, polymer melt and solution phases, deeply modifying the rheological properties of the material3. However, polymer chain entanglement is far from being well understood4. Starting from these observations, we simulated at HF/6-31G* level an entangled polyethylene chain in different open or ring-closed configurations as trefoil-, figure eight- or slip-knots, and intermolecular links. The stability of the configurations and maximum potential energy which can be stored into a knot have been evaluated. Also, the mechanisms of stress relaxation have been followed. We found out that in a knot it is possible to store a deformation energy much higher than a C-C bond energy and the chains can relax to entangled configurations with a stability similar to that of the free-chain, highlighting the role which can be played by entanglements in raising the rheology of polimeric or nanocomposite materials.
Figure. Entangled polyethylene models (452 atoms): trefoil- (left), figure eight- (middle) and slip-
knot chain (right).
References 1. N. M. Pugno, PLoS One 2014, 9, e93079. 2. M. Doi and S. F. Edwards, The Theory of Polymer Dynamics, Oxford Science Publications 1990. 3. J. T. Padding and W. J. Briels, J. Phys.: Condens. Matter 2011, 23, 233101. 4. A. E. Likhtman and M. Ponmurugan, Macromolecules 2014, 47, 1470.
P25
Theoretical investigation of vibrationally resolved electronic transitions in
Europium complexes Ugo Cosentino1, Claudio Greco1, Damiano Gerosa1, Giorgio Moro2, Alberto Baiardi3, Vincenzo Barone3
1Dipartimento di Scienze dell’Ambiente e del Territorio e di Scienze della Terra, Università di Milano-Bicocca; Piazza della Scienza 1, 20126 Milano, Italy;2Dipartimento di Biotecnologie e
Bioscienze, Università di Milano-Bicocca; Piazza della Scienza 2, 20126 Milano; 3Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
Due to their photophysical properties, Lanthanide complexes with π-conjugated ligands can act as light antennae, and thus find applications in several technological fields. [1] In particular, europium complexes with β-diketonate ligands (β-DK) have attracted special interest in optoelectronic applications because of their strong and narrow red emission. Recently, [2] a series of novel nona-coordinated europium complexes with oxadiazole substituted 1,10-phenantroline and β-DK ligands has been synthetized and experimentally characterized. These complexes present high photoluminescence (PL) quantum yields and improved carrier-transporting abilities, which makes them interesting for electroluminescence (EL) applications as organic light-emitting diodes (OLEDs). For complexes 1 – 3 (Scheme 1) absorption spectra have been reported together with fluorescence spectra of the free ligands, both collected in dichloromethane solution. Moreover, triplet energy levels have been determined from the phosphorescence spectra of the corresponding gadolinium complexes collected in ethanol at 78 K.
In the present contribution, we applied a recently developed approach for the calculation of vibrationally resolved electronic absorption and emission spectra of large and flexible molecules [3] to calculate the spectra of these systems in the framework of the Franck-Condon (FC) approximation using the adiabatic Hessian (AH) model. Calculations were performed at the DFT theory level, using the PBE1PBE and the CAM-B3LYP functionals. As previously noticed in the case of analogous rare earth complexes, [4] the adopted computational approach led to a satisfactory reproduction of experimental evidences, allowing a deeper insight in the involved molecular processes. References [1] J-C. G. Bünzli, C. Piguet Chem. Soc. Rev. 2005, 34, 1048. [2] Z. Chen, F. Ding, F. Hao, M. Guan, Z. Bian, B. Ding, C. Huang, New J. Chem. 2010, 34, 487. [3] A. Baiardi, J. Bloino and V. Barone, J. Chem. Phys. 2016, 144, 084114 [4] C. Greco, G. Moro, L. Bertini, M. Biczysko, V. Barone, U. Cosentino J. Chem. Theory
Comput. 2014, 10, 767.
Scheme 1
P26