[CP2K-user] [CP2K:13945] Re: Large energy difference between md step and single point calculation

Massimo Bocus massib... at gmail.com
Tue Sep 22 11:05:36 UTC 2020

Dear Marcella,

I used that reference cell parameters as they derive from a static
optimization, then they relax and equilibrate during the npt run. Does cp2k
actually maintain the plane waves basis set size during the md run so that
once I do a single point calculation with the same pw energy cutoff the
number of pw is different? And could this in your opinion justify the
observed energy difference?

Thank you very much for the suggestion,

On Tue, 22 Sep 2020 at 12:04, Marcella Iannuzzi <marci... at gmail.com>

> Dear Massimo
> In the MD the reference cell is used, which is quite different from the
> cell of the single point calculation.
> Kind regards
> Marcella
> On Tuesday, September 22, 2020 at 10:55:14 AM UTC+2 mas... at gmail.com
> wrote:
>> Dear CP2K users/developers,
>> I am extracting some snapshots from an umbrella sampling simulation (with
>> PLUMED as dependency of CP2K 5.1) and I would like to recalculate their
>> energy at a higher level of theory. So to start I performed a single point
>> calculation at the same level of theory of the US simulation (PBE-D3) and,
>> surprisingly for me, I got very different results in the energy. In
>> particular, the energy of the MD step is:
>> ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
>> -3520.987951048081868
>> While for the single point calculation:
>> ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
>> -3520.903314334958850
>> Which is an enormous difference. Attached the two input scripts, the main
>> differences being the RUN_TIPE, the cell parameters (for the single point
>> they are just taken from the md output at the selected step) and the lack
>> of the MOTION section.
>> Does anybody have an idea on where this large energy difference could
>> come from?
>> Thank you in advance,
>> Massimo Bocus
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