[CP2K-user] [CP2K:13943] Large energy difference between md step and single point calculation

[HB H]

Hi Massimo,

I believe the easiest way to figure out what is going on here, is to run a
few MD steps with their wavefunction saved. And try single point
calculations with and without wavefunction from scratch.

This should be very quick and looking forward to your reply~.~

Cheers,
Haibei

Massimo Bocus <massib... at gmail.com> 于2020年9月22日周二 下午5:34写道：

> Dear Haibei,
>
> Thank you for your kind reply. I completely agree with you, however I
> think that if reading the wavefunction makes the final output energy change
> by 200 kJ/mol with respect to a calculation "from scratch" then there must
> be something conceptually wrong in how the code treats the two cases.
> Moreover, it is completely impossible for me to save the wavefunction for
> every step as the size of the file is about 30MB and I cannot know in
> advance which steps I am going to take for the single point calculations.
> If you have any other idea on how the problem could be solved, I would be
> happy to know.
>
> Best regards,
> Massimo
>
> On Tue, 22 Sep 2020 at 11:22, HB H <haibe... at gmail.com> wrote:
>
>> *Hi  Massimo,*
>>
>> I think in MD simulations, the energy of one step is calculated not only
>> based on the geometry, but also wavefunction of the last step. While the
>> single point calculation only relies on the geometry.
>>
>> That being said, you should save the wfn files of each MD steps and use
>> them as the restart wfn for single point calculations.(i.e. add "
>> *WFN_RESTART_FILE_NAME* *XXXXX-RESTART.wfn*" in "DFT" section)
>>
>> Let know if I was wrong or not.
>>
>> Cheers,
>> Haibei
>>
>>
>> Massimo Bocus <massib... at gmail.com> 于2020年9月22日周二 下午4:55写道：
>>
>>> 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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