Transcript FCC structures - Electron poor materials

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 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
NELMIN = 8
NFREE = 20
| keep dielectric function between ionic movements
| minimum number of electronic steps
| 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
• 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_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
.
Electronegativity (EN)
using Pauling Scale
ACF.dat :
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
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
ACF.dat :
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
ENSb – ENIn = 0.27
Bader charge shift = 0.3999
ACF.dat :
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
ENSb – ENGa = 0.24
Bader charge shift = 0.2978
ACF.dat :
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
ENSe – ENZn = 0.9
Bader charge shift = 0.7286
ACF.dat :
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
ENTe – ENZn = 0.45
Bader charge shift = 0.5102
ACF.dat :
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
ENTe – ENZn = 0.0
Bader charge shift = 0.0319
FCC Comparisons
Compound Name EN1-EN2
Si
0
GaSb
0.24
InSb
0.27
ZnTe
0.45
GaAs
0.37
ZnSe
0.9
Bader
0.0319
0.2978
0.3999
0.5102
0.6237
0.7286