1. Theory- Si an exploration of what is a bond via charge density.
Electron poor materials research group
Group meeting Nov 11, 2010
Theory- Si an exploration of what is a bond via charge density.
volume of

2. Procedure
Static Calculations of the 4 FCC structures were computed from accurate relaxation (see previous weeks precentation)
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

3. Si - Atom location and charge Bader analysis
ACF.dat :
# X Y Z CHARGE MIN DIST ATOMIC VOL
VACUUM CHARGE:
VACUUM VOLUME:
NUMBER OF ELECTRONS:
Bader charge shift =

4. Si atomic bounding box according to Bader

5. Charge density Isosurfaces
High charge density of valence electrons electrons/Å3 (I think :P)
Vesta claims 0.08
volume of cubic cell is angs^3
8 valence electrons in cell. 8/ =

6. Subtracted Charge density
Calculate charge density of crystal. CHGCAR
Now calculate the charge density of each of the atoms within the crystal individually using the same lattice constants and same input parameters.
Subtract the charge density of individual (CHGCAR-1, CHGCAR-2 …) atoms from the charge density of the crystal. Giving a resultant charge denstiy ρf.

7. Subtracted charge density. ρf > 0
Here the isosurface lies in line directly between bonded Si Atoms

8. Subtracted charge density. ρf < 0
Here the isosurface lies in a line with the Si-Si bonds but on the opposite side of the nearest bonding atom.

9. Subtracted charge density. ρf > 0 is yellow, ρf < 0 is blue

10. Subtracted charge density. Slice of charge density.

11. Subtracted charge density. Slices of charge density.