[CP2K-user] [CP2K:14633] Re: Spin Contamination "Rule of Thumb?"

[Stephen Vicchio]

Hi  Vladimir,

Thanks for the response! What would you say about the difference in ideal
and single determinant spin states that are Delta_S**2 = ~0.1-0.2? I have a
few calculations where the ideal S**2 is 6.00000 and the single determinant
S**2 is 6.150000.

I found a rule for Gaussian calculations where the difference should be
less than 10% of the ideal S**2. However, is that a reasonable assertion
for all UKS DFT calculations?

With much appreciation,

Stephen

On Mon, Jan 25, 2021 at 6:50 AM Vladimir Rybkin <rybk... at gmail.com> wrote:

> Dear Stephen,
>
> the "cutoff" is what you find reasonable. To me, 12.019722 is practically
> no contamination, whereas delta=2.0 is a large one and the results are
> likely unreasonable. At least, you will not likely be able to get the
> latter published.
>
> Yours,
>
> Vladimir
>
> пятница, 22 января 2021 г. в 20:55:03 UTC+1, Stephen:
>
>> Hi All,
>>
>> I'm performing a few calculations of Ni(II) atom supported on a
>> metal-organic framework. The Ni(II) atoms can exhibit different spin
>> states, which means I must run UKS T while varying MULTI to account for all
>> the configurations.
>>
>> Is there a specific rule for spin contamination when looking at the S**2?
>> For example,
>>
>>   Ideal and single determinant S**2 :                   12.000000
>> 12.019722
>>
>> I've assumed that this particular structure has no spin contamination, I
>> have some other calculations where the difference between the ideal and
>> single determinant spin states is much larger (Delta_S**2 = ~2.00).
>>
>> Does anyone have an appropriate cutoff for spin contamination?
>>
>> With much appreciation,
>>
>> Stephen
>>
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-- 
*Stephen P. Vicchio*
PhD Candidate | Getman Research Group
Dept. of Education GAANN Fellow
Director of Student Organization Finances, Graduate Student Government
Department of Chemical & Biomolecular Engineering
<https://www.clemson.edu/cecas/departments/chbe/>
105 Earle Hall | Clemson, SC 29634-0909
svi... at g.clemson.edu
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