[Pw_forum] implementation of variation of occupations and Fermi level with perturbations

Paolo Giannozzi giannozz at democritos.it
Tue Apr 19 22:44:55 CEST 2011

On Apr 8, 2011, at 20:39 , David Strubbe wrote:

> Eq. 79 refers to a quantity \Delta n_{ext} and an integral of the LDOS
> with \Delta V_{SCF} to calculate the shift in Fermi level. However in
> ef_shift it appears that the density response drhoscf is used instead
> of these quantities in the numerator, which doesn't seem like the  
> same thing.

it doesn't, but it is. The (dirty) trick is well hidden in the call  
to routine dv_of_drho:
it accepts in input the variation of the charge density, returns in  
output the
variation of the potential, overwritten on the former. It was done a  
looong time
ago in order to spare some memory, when machines had much less ram and
the code was much simpler and smaller (occasional dirty tricks were  
control, sort of). A comment in the code would have spared you (and me)
some time. Unfortunately comments in code tend to belong to one of the
following categories: 1) useless, 2) misleading, 3) obsolete, 4)  

Paolo Giannozzi, Dept of Chemistry&Physics&Environment
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

More information about the users mailing list