superposition of atomic charge densities

[dholec]

Hello VASP users & developers!

I would like to plot a difference between the crystal electron density and the superposition of the atomic charge densities to see how the charge redistributes when the bonds are created. How can I obtain this?

My understanding is that I am basically looking for the charge density which is the staring guess with ICHARG=2. So I tried so force VASP to do only initialisation and then immediately to escape the electronic cycle (by setting NELM=0, EDIFF=10E5 and, to be completely on a safe side, NELMDL=-5). However, what the density I obtain this way looks very suspicious - in fact it looks like there is some charge missing in the corners of the NaCl-like cubic unitcell. When I do the same thing with supercell 3x3x3, the charge in the middle unitcell looks good (i.e. no charge seems to be missing) and the corners of this big supercell are missing much less charge than in the case of the unit cell.

Is there something fundamentally wrong in my procedure? How shall I do this right?

Thanks a lot in advance!
David

[admin]

Even if you want 'atomic charge densities', please allow for a few electronic steps (EDIFF=10-5, NELM=60 ): VASP usually starts with a random wavefunction (not with atomic orbitals!) therefore, even in ICHARG=2, the charge denities corresponding to superposed atomic potentials has to be converged to the self-consistent solution of a Hamiltonian constructed from (a fixed) V corresponding to (non-updated!) superposed atomic potentials. for ICHARG=2, this V is not updated to converge to the solution of interacting atoms.