My Community

hi,
i would be thankfull to anyone give me some comments.

problem::
in my band structure calculations, the topmost empty bands (conduction bands) are always zig-zag like, they are never optimized well. but the rest of the bands are quite nice.

the system is a nanotube, (altough i have tested silicon too, but same problem).

ECUT and FFT meshes were quite high.
ISMEAR =0 always
ISTART=0 always
i have followed all the steps in the vasp manual.

1).... got a charge density (ICHARG=2) with a dense k-mesh (1 1 18) over the initially optimized structure.

2).... and used ICHARG=11 with 1 1 30 kpoints to calculte the band energies.

in this case there was 40 filled (80 electrons) and 20 empty bands.
the problem is not related to plotting software, i have checked that.

thanks for any suggestions.
h. yilmaz

DFT is a ground state theory...

thanks alot Admin.

so i guess, i am not doing anything wrong. i should not care about the uppermost empty bands.

yes, DFT ONLY optimizes the occupied bands (please have a look at the basic papers of Kohn and Sham, and Hohenberg and Kohn).

Is there a way to tell vasp to calculate the unoccupied states exactly as well? For example, the unoccupied states a few eV above the Fermi energy are useful in analysis. Thank you.

no, not within standard DFT. The best approaches to do it are TDDFT or GW. GW will be included in the new vasp release 5.1 (please have a look at out homepage).