[CP2K-user] [CP2K:16493] Re: IR spectm for NaCl under PBC

[fabia...@gmail.com]

Dear Victor,

You need a much tighter convergence criterion for the optimization prior to 
the vibrational analysis. You increased MAX_FORCE to 5e-3 (guessing from 
the output), instead you have to decrease it to at least 1e-5, maybe even 
lower.
CP2K prints the forces for the replica in the output. The forces under 
"Minimum Structure - Energy and Forces:" should be more or less 0 and 
considerably differ between the other images. Currently you are computing 
the vibrational analysis from almost pure noise. 

Cheers,
Fabian
On Sunday, 23 January 2022 at 19:58:05 UTC+1 volk... at gmail.com wrote:

> Dear colleagues:
> here is the normal mode analysis I could manage by now for NaCl under PBC.
>
> There is only one unit cell: previously, I reported that I could not 
> configure CP2K to reproduce NaCl structure using multiple cells 2 2 2.
> There are strange distortions, which I did confirm to sustain under 
> different CUTOFF values (1000 and 600), and regardless if dispersion is 
> switched off or not.
>
> When a single cell under PBC, optimization leads to the “right” structure, 
> when ESP 10^-12.
>
> However, the negative(imaginary) frequencies are many and they are very 
> large.
> I may anticipate that the “miss performance” is enhanced due to the PBC.
>
> Eventhough the results are "devastating",
> :-)
> nonetheless, I find this might be very good, very helpful – I got an idea.
>
> Dear Dr. Hutter,
> is it possible that CP2K may have an “issue” about positioning a structure 
> in respect to both, in respect to the FT grind and in respect to the PBC.
> Perhaps, there could be a relative mismatch phenomenon, which could 
> stimulate artificial transition states with negative frequencies?
>
> May be, what I observe is that PBC on the unit cell helps to sense this 
> better?
>
>
> Thank you for your time and for any comments.
>
> With best regards,
> Sincerely
> Victor
>

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