[QE-users] Computing Charge Density Differences

[Paolo Giannozzi]

On Sun, Mar 22, 2020 at 5:50 PM Victor Bermudez <bermudez at alum.mit.edu>
wrote:


> I'm trying to compute the charge density difference for a molecule on a
> substrate [...] using Postprocessing (pp.x, plot_num=7)


you should first of all try with the charge density  (plot_num=1) and check
whether you get sensible numbers

        I'm aware that all densities have to be obtained with the same atom
> positions, ecutwfc, ecutrho, etc., and I've done that.


and same cell

        *** vdW-TS term will be missing in potential ***
>

as long as you are interested in the charge density, this should be
harmless. The initialization of the vdW-TS terms is missing in
postprocessing (for some obscure reasons, it crashed)

Paolo


(2)  The molecule is paramagnetic, so the SCF calculations for n(mol.+slab)
> and n(mol.) were spin-polarized, but that for n(slab) was not. In obtaining
> Diff(n) I'm using the highest majority-spin bands for n(mol.+slab) and
> n(mol.).
>         Can I then use the highest doubly-occupied band for n(slab) if I
> set w2/w1 = 0.5 ?
>         Do I have to do a spin-polarized calculation for n(slab) even
> though it's diamagnetic ?
>         Is further adjustment of w2/w1 need to account for the fact that
> mol.+slab and slab involve a different total number of electrons ?
>
> (3)     The slab comprises a 4x4 supercell with 1 molecule. Should I then
> set w3/w1 = 1/16 ? Again, is any further adjustment of w3/w1 needed ?
>
> (4)     In the SCF calculations of n(mol.+slab) and n(slab) I used a 3x3
> MP grid (because of the large supercell). For n(mol.), on the other hand, I
> used just the gamma point (because the isolated molecules are far apart).
>         Is that OK, or should I have used the same MP grid in obtaining
> n(mol.) ?
>
> Thanks in advance for your help.
>
> Best Wishes,
> Vic Bermudez
> U.S. Naval Research Laboratory (retired)
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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