[Q-e-developers] potentially unnecessary initial computation of sc

[Paolo Giannozzi]

On Mon, 2014-01-20 at 14:13 -0600, Maxwell Hutchinson wrote:

> In the initialization part of the Davidson solver, cegterg, sc is
> computed from evc with a zgemm and mp_sum.  evc should be coming into
> cegterg already orthonormalized, so this should be unnecessary.  Are
> there cases where this is not true?

if you have ultrasoft pseudopotentials or PAW, wavefunctions (evc) are
not orthonormal. Since the S matrix is not saved from the previous 
self-consistency step, it has to be recalculated in any case. For
norm-conserving PP's, this should not be needed, but the way it is
implemented now guarantees that the routine works (or doesn't fail)
even if input wavefunctions are not normalized. I suspect that this
is actually used in Molecular Dynamics run, when wavefunctions are
extrapolated: ther eis no guarantee that they are orthonormal. 

P.

> Unless very little refinement is necessary, this won't affect
> performance much.  It's shorter, though.  See:
> https://github.com/maxhutch/quantum-espresso/commit/69f5c2dba36945a9d0ed3f8ece5e8a768f1316a2
> 
> 
> 
> Thanks,
> Max
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-- 
 Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
 Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
 Phone +39-0432-558216, fax +39-0432-558222