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

[David Strubbe]

Hello,

I am still wondering about this question and haven't gotten any response.
Can anyone help clarify the relation between the equations in the Rev Mod
Phys paper and the code?

Thanks,
David Strubbe
UC Berkeley

On Fri, Apr 8, 2011 at 11:39 AM, David Strubbe <dstrubbe at berkeley.edu>wrote:

> Dear developers,
>
> I am trying to understand how the variation of occupations and Fermi level
> is implemented in density-functional perturbation theory for metals. In the
> Baroni, de Gironcoli, and Dal Corso Rev Mod Phys paper on DFPT, this issue
> appears in equations 68 and 75-79. I see that routine ef_shift can implement
> the result of a shift in the Fermi level as in either eq. 68 or eq. 75
> depending on the value of "flag". But for the calculation of the shift
> itself, I do not see the correspondence between what is done in the code and
> the equations in the paper. 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. Can you explain what the relation is between the calculation
> in the code and the equations in the RMP paper?
>
> Thank you,
> David Strubbe
> UC Berkeley
>
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