[CP2K:2638] difference between Total energy and ENERGY| Total FORCE_EVAL ( QS ) energy ?
Juerg Hutter
hut... at pci.uzh.ch
Tue Mar 23 08:20:26 UTC 2010
Hi
my guess would be that
MULTIPLICITY 73
is the problem. There is a high probability that you converged
in an excited state (and there are probably an enormous
amount of them with close energy) and when you restart
or make an MD/geometry move you will find another state.
The only way I can see that such a calculation is feasible
is with non-collinear spin, a method not implemented in cp2k.
regards
Juerg Hutter
----------------------------------------------------------
Juerg Hutter Phone : ++41 44 635 4491
Physical Chemistry Institute FAX : ++41 44 635 6838
University of Zurich E-mail: hut... at pci.uzh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
----------------------------------------------------------
On Mon, 22 Mar 2010, Jun wrote:
> Hi all,
>
> When doing electronic structure calculations in MD or geo_opt, it is
> very often to see a small difference in energy between "Total
> energy: **** " and " ENERGY| Total FORCE_EVAL ( QS ) energy
> (a.u.): **** " in output files. The difference is usually so small
> that I thought it is just due to numerical error. (I am not saying the
> difference due to applying some restraining potentials or in MIXED
> calculations). However, I recently noticed that the difference can be
> as large as 0.1 eV, which makes me wonder what is difference in
> definitions of "Total energy " and "ENERGY| Total FORCE_EVAL ( QS )
> energy". An example is as follows: (input file (input.inp) is
> uploaded)
>
> I have repeated the same ENERGY_FORCE calculation three times (there
> may be some differences in the initial guess for wavefunction because
> I used SCF_GUESS RESTART.), the energies I got are
> 1. Total energy:
> -3269.58265002363760
> ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
> -3269.578462626209330
>
> 2. Total energy:
> -3269.57862048247534
> ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
> -3269.578462728981776
>
> 3. Total energy:
> -3269.57793566477721
> ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
> -3269.578462722795848
>
> In three cases, " ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.)" are
> almost the same, but "Total energy: " are quite different. Especially
> for case 1, the difference is up to 0.1 eV.
>
> Any suggestion and comment are appreciated.
>
> Cheers,
> Jun
>
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