Electron poor materials research group

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

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: 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

3. Si - Atom location and chargeBader analysis 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 Bader charge shift = 0.0319

4. Si atomic bounding box according to Bader

5. Charge density Isosurfaces High charge density of valence electrons. 0.24 electrons/Å3 (I think :P) Vesta claims 0.08

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.