[Q-e-developers] recompute the total energy after scf is finished

[Lorenzo Paulatto]

On 11/04/2013 01:16 PM, stefano de gironcoli wrote:
> ciao Lorenzo,
>   I think
>      deband = delta_e() = - \int v_(r) rho_r(r) dr
>   should be computed with the potential that generated the wfcs and 
> not with the one obtained from the new density
>   In this way i exactly cancel the corresponding term in eband

Yes, that would work, but I cannot do it: as I'm restarting after the 
end of the calculation the potential is immediately recomputed from rho. 
The same actually happens when doing an nscf calculation, i.e. the 
wavefunctions you recompute from a nscf calculations are not from the 
same potential as the one from the corresponding scf calculation. I 
noticed now that you can see some small differences in the eigenvalues.

At least I understand the discrepancy now. I think for the moment I'll 
stick to using a very strict convergence threshold while keep think 
about it.

For who's interested: What we're trying to do in the end is to freeze 
the ground-state wavefunctions and potential. Then change the 
occupations, recompute rho accordingly and recompute the total energy 
from the new wfc/rho in the old ground-state potential. There are a few 
conceptual problems about what has to be new and what old. Reproducing 
the same energy was just the first step.

cheers and thanks

-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
+33 (0)1 44 275 084 / skype: paulatz
http://www-int.impmc.upmc.fr/~paulatto/
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