[gpaw-users] total energy difference for optimization and single point calculation

[Ask Hjorth Larsen]

Hi Henrik

On Tue, 23 Nov 2010, Henrik Oberg wrote:

> Hi,
> this maybe a stupid question but why do I get a difference in total
> energy when I geometry optimize a structure and subsequently do a
> single point calculation on the optimized structure using the same
> calculation parameters?
> The difference lie in the 4th decimal, but still...
> Best regards
>
> Henrik
>
> ------------------------------------------------------------
> Henrik Öberg 	henrik.oberg at fysik.su.se
> FYSIKUM, AlbaNova, Stockholm University
> S-106 91 Stockholm, Sweden
>
> Phone:  +46-8-5537 87 21
> Mobile: +46-(0)70-491 02 64
>
>
>
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>

My guess:

The SCF convergence criterion is on the order of 4th-decimal precision, 
and the calculations had different initial conditions:  One was started 
from an LCAO initialization (i.e. from scratch) while the other was 
reusing the KS WFs from the previous relaxation step.

Regards
Ask