Intermolecular interaction ofwater hexamerwater hexamer

Yiming ChenOctober 5th, 2009

Contents

• Background Information

Previous Investigations

• Energy Decomposition Analysis of Water Hexamer

• Acknowledgement

Contents• Background Informat ion

Intermolecular Interaction

• Water Clusters

• Energy Decomposition Analysis

Previous Investigations

• Energy Decomposition Analysis of Water Hexamer

• Acknowledgement

Intermolecular Interaction

• Forces act between stable molecules.

Categories

• London Dispersion Force

• Dipole-Dipole Interaction

• Hydrogen Boding

Water Cluster

• Definition: discrete hydrogen bonded assembly or cluster of molecules of water

• Examples: Dimer, Trimer, Tetramer, Pentamer, Hexamer, and etc.

Water Cluster

The Cambridge Cluster Database

Water Cluster

• Why we study water clusters?

Understanding cloud and ice formation

• Solution chemistry

• Large number of biochemical processes

Molecular Dynamics

Energy Decomposition Analysis (EDA)

• Definition: Decompose total interaction energy from a supermolecule calculation into several energetic terms.

Example: Intermolecular interaction in water dimer with LMOEDA method (kcal/mol) *

Electrostatic Energy

Exchange Energy

Repulsion Energy

Polarization Energy

Dispersion Energy Total Energy

-8.41 -8.85 16.01 -2.38 -1.33 -4.95

* THE JOURNAL OF CHEMICAL PHYSICS 131, 014102 (2009)

Contents• Background Information

Previous Invest igat ions

• Experimental Studies

• Theoretical Studies

• Energy Decomposition Analysis of Water Hexamer

Acknowledgement

Experimental StudiesObjective: Use sophisticated spectroscopic tools (like Far-infrared (FIR) vibration-rotation-tunneling (VRT) spectroscopy) to determine the structure of water clusters.

Experimental Studies

The structures of (H2O)n (n=6-20) clusters have been characterized by spectroscopy method;

• Different structures of water clusters in different phases (Solid, gas, crystal) are detected;

Supramolecular structures in bulk water is still difficult to study by experimental method.

Theoretical Studies• Structures: larger clusters are predicted,

like W20-W28 (bucky water), icosahedral network;

• Energy: Energetic low-lying clustersare found by theoretical calculation;

• Studies focus on intermolecular interactions are still rare.

Contents• Background Information

Previous Investigations

• Energy Decomposit ion Analysis of Water Hexamer

Introduction of investigation

• Intermolecular interactions of water hexamers

• Many-body interaction: additivity of energy terms

• Acknowledgement

Target of Investigation

• (H2O)n clusters are planar when n=1-5;

Eight low-lying water hexamers are taken: prism, cage, bag, chair, book & boat;

Method of Investigation

• Software: Gamess ver. 118 (Aug. 14, 2009);

Geometry Optimization: MP2/aug-cc-pVTZ;

EDA: LMOEDA method proposed by Su and Li* is taken to study the physical origins of intermolecular interactions, at MP2/aug-cc-pV5Z level;

* THE JOURNAL OF CHEMICAL PHYSICS 131, 014102 (2009)

Method of Investigation

• LMOEDA: Total interaction energy will be decomposed into five terms: electrostatic ( EΔ es), exchange ( EΔ ex), repulsion ( EΔ rep), polarization ( EΔ pol), dispersion ( EΔ disp);

• To evaluate the energy changes aroused by the distortion of geometry, the energetic differences between free water molecule and water in hexamer are calculated, called “Preparation Energy” ( EΔ pre).

* THE JOURNAL OF CHEMICAL PHYSICS 131, 014102 (2009)

Intermolecular Interactions of Water Hexamers

Cluster EΔ pre EΔ es EΔ ex EΔ rep EΔ pol EΔ disp EΔ total

Prism +1.32 -81.98 -103.15 +187.66 -34.69 -15.26 -46.09Cage +1.28 -82.67 -105.31 +192.51 -36.58 -15.28 -46.05Bag +1.52 -82.36 -107.29 +197.61 -40.27 -14.10 -44.88Chair +1.32 -81.87 -105.83 +196.33 -43.03 -11.87 -44.95Boat-1 +1.33 -80.04 -103.75 +192.30 -41.82 -11.98 -43.96Boat-2 +1.30 -79.64 -103.09 +191.02 -41.62 -11.84 -43.87Book-1 +1.37 -83.38 -107.24 +197.70 -40.39 -13.84 -45.78Book-2 +1.40 -83.14 -106.79 +196.80 -39.81 -13.92 -45.46

Unit: kcal/mol

Intermolecular Interactions of Water Hexamers

• Conclusion:

different terms have various contributions to total interaction energy;

• Absolute value of repulsion roughly equals to the sum of electrostatic energy and exchange energy;

Many-body interactions

• Two-body and three-body interactions of eight hexamers are studied, four-body interactions of most low-lying prism and cage clusters are studied.

• Additivity of different energy terms are discussed separately.

Many-body interactions• Additivity: the total interaction energy term

equals to the sum of energy terms of each pair of water molecules.

In two-body study, the total electrostatic energy equals to the sum 15 pairwise energy terms in water hexamers:EΔ es (TOTAL) = EΔ es (12)+ EΔ es (13)+ EΔ es (14)+ EΔ es (15)+ EΔ es (16)+ EΔ es

(23)+ EΔ es (24)+ EΔ es (25)+ EΔ es (26)+ EΔ es (34)+ EΔ es (35)+ EΔ es (36)+ EΔ es (45)+ EΔ es (46)+ EΔ es (56)

• The total energy could be considered as “Six-Body” interaction energy.

Many-body interactions

Cluster EΔ es EΔ ex EΔ rep EΔ pol EΔ disp EΔ total

Two-BodyInteraction

Prism -81.98 -103.15 +188.49 -25.82 -15.15 -37.64Cage -82.67 -105.30 +193.30 -27.54 -15.18 -37.43Bag -82.36 -107.30 +198.45 -29.44 -15.03 -34.55Chair -81.86 -105.85 +196.95 -29.98 -11.71 -32.39Boat-1 -80.05 -103.76 +192.95 -29.34 -11.77 -31.98Boat-2 -79.63 -103.10 +191.67 -29.11 -11.69 -31.87Book-1 -83.38 -107.26 +198.36 -29.50 -13.67 -35.36Book-2 -83.14 -106.79 +197.44 -29.25 -13.72 -35.46

Three-BodyInteraction

Prism -81.98 -103.15 +188.26 -27.93 -15.15 -39.94Cage -82.67 -105.31 +193.09 -29.69 -15.20 -39.78Bag -82.35 -107.29 +198.23 -31.89 -15.03 -34.55Chair -81.86 -105.82 +196.80 -32.78 -11.68 -35.35Boat-1 -80.04 -103.76 +192.78 -32.04 -11.78 -34.84Boat-2 -79.64 -103.16 +191.62 -31.86 -11.68 -34.70Book-1 -83.38 -107.24 +198.19 -31.95 -13.68 -38.05Book-2 -83.13 -106.79 +197.28 -31.67 -13.74 -38.05

Four-BodyInteraction

Prism -81.98 -103.15 +188.05 -30.10 -15.18 -42.35Cage -82.67 -105.31 +192.88 -31.91 -15.21 -42.22

Unit: kcal/mol

Many-body interactions• Conclusion

• The electrostatic energy ( EΔ es) and exchange energy ( EΔ es) are strictly additive;

• Repulsion energy ( EΔ rep) and dispersion energy ( EΔ disp) are roughly additive (in 1 kcal/mol);

• Polarization energy ( EΔ pol) is not additive at all, it totally dependent on the scale of system.

Contents

• Background Information

• Previous Investigations

• Energy Decomposition Analysis of Water Hexamer

• Acknowledgement

Acknowledgment

• Dr. Hui Li

• Dr. Barry Cheung

• Dr. Peifeng Su

• Dejun Si

• Nandun Thellamurege

Thank you!