Electron poor materials research group

Group meeting Nov 11, 2010

Theory- Bader Analysis -> FCC

This is version 2 with larger NG(X,Y,Z)F values for more accurate charge density grids

Pre-Procedure• Very accurate Equation of state (EOS) calculations are

preformed to find the optimum relaxed volume of the structure. This EOS is fitted to a Birch-Murnaghan equation.– 11X11X11 kpoint gamma grid– PREC=ACCURATE– ENCUT=1.3*(ENMAX in POTCAR)– Psuedo-potential is PAW_PBE

• A final very accurate final relaxation if preformed to bring the structures to their final relaxation volume given by EOS– see next slide for INCAR for relaxation

INCAR for final relaxationSystem = Si relaxsetup.sh

NSW = 20 | number of ionic stepsISIF = 4 | (ISIF=2 Relax ions only, ISIF=3 Relax everything)IBRION = 1 | ionic relaxation algorithmEDIFF = 1E-9 | break condition for elec. SCF loopEDIFFG = -1E-8 | break condition for ionic relaxation loop

MAXMIX = 80 | keep dielectric function between ionic movementsNELMIN = 8 | minimum number of electronic stepsNFREE = 20 | number of degrees of freedom (don't go above 20)

#RECOMMENDED MINIMUM SETUP#GGA= #xchange-correlation#VOSKOWN= #=1 if GGA=91; else = 0PREC = ACCURATE #PRECISION, sets fft gridENCUT = 320 #energy cutoff, determines number of lattice vectorsLREAL = .FALSE. #.FALSE. MEANS USE RECIPROCAL LATTICEISMEAR = 0 #determines how partial occupancies a set.

Procedure• Static Calculations of the 4 FCC structures were computed from

accurate relaxation (see previous slides) – Calculations were done on a Gamma 11X11X11 grid– USED NG(X,Y,Z)F of 6XNG(X,Y,Z) for accurate charge density grid.– An extra flag was used in the INCAR file: LAECHG = .TRUE.

• Turns on All Electron CHGCAR file outputs and outputs 3 files• AECCAR0: core charge density• AECCAR1: atomic AE charge density (overlapping atomic charge density)• AECCAR2: AE charge density

• The files AECCAR0 and AECCAR2 are added together for bader analysis per instructions: http://theory.cm.utexas.edu/bader/vasp.php– chgsum.sh AECCAR0 AECCAR2, chsum is a shellscript

• Outputs CHGCAR_sum

• Bader analysis is done on the vasp CHGCAR from the static run– bader.x -p atom_index -p bader_index CHGCAR -ref CHGCAR_sum

• atom_index: Write the atomic volume index to a charge density file• bader_index: Write the Bader volume index to a charge density file

NOTES• Only the PAW potentials can output there core charges for bader

analysis• A fine fft grid is needed to accurately reproduce the correct total

core charge. It is essential to do a few calculations, increasing NG(X,Y,Z)F until the total charge is correct.

• The outputs from bader.x are:– ACF.dat – Atomic Coordinate file. Shows the location and charge of the

atoms– BCF.dat – Bader Coordinate file.– AVF.dat – Atomic Volume file. Used to keep track of other files that may

be output with the bader program with flag –p all_atom– AtIndex.dat (only with –p atom_index) – charge density file which

contains the atomic borders– BvIndex.dat (only with –p bader_index) –charge density file which

contains the bader borders

INCAR_staticSystem = Si

SIGMA = 0.01

#RECOMMENDED MINIMUM SETUPPREC = ACCURATE #PRECISIONENCUT = 320LREAL = .FALSE. #.FALSE. MEANS USE RECIPROCAL LATTICEISMEAR = 0 #USE GAUSSIAN SMEARING

#FOR GW CALCULATIONS#LOPTICS = .TRUE.#NBANDS = 96

#FOR BADER ANALYSISLAECHG=.TRUE.NGXF = 120 #USE 6X NGX for bader analysisNGYF = 120NGZF = 120.

Electronegativity (EN)using Pauling Scale

GaAs# X Y Z CHARGE MIN DIST ATOMIC VOL -------------------------------------------------------------------------------- 1 0.0000 0.0000 0.0000 2.3763 1.0539 18.1315 2 1.4409 1.4409 1.4409 5.6237 1.2766 29.7299 -------------------------------------------------------------------------------- VACUUM CHARGE: 0.0000 VACUUM VOLUME: 0.0000 NUMBER OF ELECTRONS: 8.0000

ACF.dat :

ENAs – ENGa = 0.37 Bader charge shift = 0.6237

GaAs Bader Volume Bounding Boxes

All other FCC bounding boxes look virtually identical to this one

InSb# X Y Z CHARGE MIN DIST ATOMIC VOL -------------------------------------------------------------------------------- 1 0.0000 0.0000 0.0000 2.6001 1.2796 29.8830 2 1.6622 1.6622 1.6622 5.3999 1.4473 43.5992 -------------------------------------------------------------------------------- VACUUM CHARGE: 0.0000 VACUUM VOLUME: 0.0000 NUMBER OF ELECTRONS: 8.0000

ACF.dat :

ENSb – ENIn = 0.27 Bader charge shift = 0.3999

GaSb# X Y Z CHARGE MIN DIST ATOMIC VOL -------------------------------------------------------------------------------- 1 0.0000 0.0000 0.0000 2.7022 1.1483 22.2941 2 1.5563 1.5563 1.5563 5.2978 1.4227 38.0197 -------------------------------------------------------------------------------- VACUUM CHARGE: 0.0000 VACUUM VOLUME: 0.0000 NUMBER OF ELECTRONS: 8.0000

ACF.dat :

ENSb – ENGa = 0.24 Bader charge shift = 0.2978

ZnSe# X Y Z CHARGE MIN DIST ATOMIC VOL -------------------------------------------------------------------------------- 1 0.0000 0.0000 0.0000 11.2714 1.0616 15.9986 2 1.4358 1.4358 1.4358 6.7286 1.3224 31.3555 -------------------------------------------------------------------------------- VACUUM CHARGE: 0.0000 VACUUM VOLUME: 0.0000 NUMBER OF ELECTRONS: 18.0000

ACF.dat :

ENSe – ENZn = 0.9 Bader charge shift = 0.7286

ZnTe# X Y Z CHARGE MIN DIST ATOMIC VOL -------------------------------------------------------------------------------- 1 0.0000 0.0000 0.0000 11.4898 1.1104 18.5303 2 1.5464 1.5464 1.5464 6.5102 1.4456 40.6387 -------------------------------------------------------------------------------- VACUUM CHARGE: 0.0000 VACUUM VOLUME: 0.0000 NUMBER OF ELECTRONS: 18.0000

ACF.dat :

ENTe – ENZn = 0.45 Bader charge shift = 0.5102

Si - For Comparison# X Y Z CHARGE MIN DIST ATOMIC VOL -------------------------------------------------------------------------------- 1 0.0000 0.0000 0.0000 3.9681 1.1316 20.2891 2 1.3672 1.3672 1.3672 4.0319 1.1051 20.6007 -------------------------------------------------------------------------------- VACUUM CHARGE: 0.0000 VACUUM VOLUME: 0.0000 NUMBER OF ELECTRONS: 8.0000

ACF.dat :

ENTe – ENZn = 0.0 Bader charge shift = 0.0319

FCC Comparisons

Compound Name EN1-EN2 BaderSi 0 0.0319GaSb 0.24 0.2978InSb 0.27 0.3999ZnTe 0.45 0.5102GaAs 0.37 0.6237ZnSe 0.9 0.7286