1. Theory- Bader Analysis -> FCC
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

2. 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

3. INCAR for final relaxation
System = Si relaxsetup.sh
NSW = | number of ionic steps
ISIF = | (ISIF=2 Relax ions only, ISIF=3 Relax everything)
IBRION = 1 | ionic relaxation algorithm
EDIFF = 1E-9 | break condition for elec. SCF loop
EDIFFG = -1E-8 | break condition for ionic relaxation loop
MAXMIX = | keep dielectric function between ionic movements
NELMIN = | minimum number of electronic steps
NFREE = | number of degrees of freedom (don't go above 20)
#RECOMMENDED MINIMUM SETUP
#GGA= #xchange-correlation
#VOSKOWN= #=1 if GGA=91; else = 0
PREC = ACCURATE #PRECISION, sets fft grid
ENCUT = #energy cutoff, determines number of lattice vectors
LREAL = .FALSE #.FALSE. MEANS USE RECIPROCAL LATTICE
ISMEAR = #determines how partial occupancies a set.

4. 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:
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

5. 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

6. INCAR_static System = Si SIGMA = 0.01 #RECOMMENDED MINIMUM SETUP
PREC = ACCURATE #PRECISION
ENCUT = 320
LREAL = .FALSE #.FALSE. MEANS USE RECIPROCAL LATTICE
ISMEAR = #USE GAUSSIAN SMEARING
#FOR GW CALCULATIONS
#LOPTICS = .TRUE.
#NBANDS = 96
#FOR BADER ANALYSIS
LAECHG=.TRUE.
NGXF = 120 #USE 6X NGX for bader analysis
NGYF = 120
NGZF = 120 .

7. Electronegativity (EN) using Pauling Scale

8. GaAs ACF.dat : # X Y Z CHARGE MIN DIST ATOMIC VOL
VACUUM CHARGE:
VACUUM VOLUME:
NUMBER OF ELECTRONS:
ENAs – ENGa = 0.37
Bader charge shift =

9. GaAs Bader Volume Bounding Boxes
All other FCC bounding boxes look virtually identical to this one

10. InSb ACF.dat : # X Y Z CHARGE MIN DIST ATOMIC VOL
VACUUM CHARGE:
VACUUM VOLUME:
NUMBER OF ELECTRONS:
ENSb – ENIn = 0.27
Bader charge shift =

11. GaSb ACF.dat : # X Y Z CHARGE MIN DIST ATOMIC VOL
VACUUM CHARGE:
VACUUM VOLUME:
NUMBER OF ELECTRONS:
ENSb – ENGa = 0.24
Bader charge shift =

12. ZnSe ACF.dat : # X Y Z CHARGE MIN DIST ATOMIC VOL
VACUUM CHARGE:
VACUUM VOLUME:
NUMBER OF ELECTRONS:
ENSe – ENZn = 0.9
Bader charge shift =

13. ZnTe ACF.dat : # X Y Z CHARGE MIN DIST ATOMIC VOL
VACUUM CHARGE:
VACUUM VOLUME:
NUMBER OF ELECTRONS:
ENTe – ENZn = 0.45
Bader charge shift =

14. Si - For Comparison ACF.dat : # X Y Z CHARGE MIN DIST ATOMIC VOL
VACUUM CHARGE:
VACUUM VOLUME:
NUMBER OF ELECTRONS:
ENTe – ENZn = 0.0
Bader charge shift =

15. FCC Comparisons Compound Name EN1-EN2 Bader Si 0.0319 GaSb 0.24 0.2978
0.0319
GaSb
0.24
0.2978
InSb
0.27
0.3999
ZnTe
0.45
0.5102
GaAs
0.37
0.6237
ZnSe
0.9
0.7286