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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.

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slide1

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
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 relaxation
INCAR for final relaxation

System = Si relaxsetup.sh

NSW = 20 | number of ionic steps

ISIF = 4 | (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 = 80 | keep dielectric function between ionic movements

NELMIN = 8 | minimum number of electronic steps

NFREE = 20 | 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 = 320 #energy cutoff, determines number of lattice vectors

LREAL = .FALSE. #.FALSE. MEANS USE RECIPROCAL LATTICE

ISMEAR = 0 #determines how partial occupancies a set.

procedure
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
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 static
INCAR_static

System = Si

SIGMA = 0.01

#RECOMMENDED MINIMUM SETUP

PREC = ACCURATE #PRECISION

ENCUT = 320

LREAL = .FALSE. #.FALSE. MEANS USE RECIPROCAL LATTICE

ISMEAR = 0 #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

.

slide8
GaAs

ACF.dat :

# 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

ENAs – ENGa = 0.37

Bader charge shift = 0.6237

gaas bader volume bounding boxes
GaAs Bader Volume Bounding Boxes

All other FCC bounding boxes look virtually identical to this one

slide10
InSb

ACF.dat :

# 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

ENSb – ENIn = 0.27

Bader charge shift = 0.3999

slide11
GaSb

ACF.dat :

# 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

ENSb – ENGa = 0.24

Bader charge shift = 0.2978

slide12
ZnSe

ACF.dat :

# 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

ENSe – ENZn = 0.9

Bader charge shift = 0.7286

slide13
ZnTe

ACF.dat :

# 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

ENTe – ENZn = 0.45

Bader charge shift = 0.5102

si for comparison
Si - For Comparison

ACF.dat :

# 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

ENTe – ENZn = 0.0

Bader charge shift = 0.0319

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