[CP2K-user] [CP2K:16477] Energy explosion when atom count increases with HFX. Issue with auxiliary basis sets?

[Nicholas Winner]

Thank you Ling. I had read this paper and noticed this problem before. I 
had even asked a similar question before on here, but the manifestation was 
slow convergence rather than divergence. I did not know that any of these 
optFIT basis sets were available.

Using the optFIT you provided, I was able to converge alpha boron without 
much issue. Do you know of any other issues where this might pop-up? i.e. 
is this just an issue of boron and carbon?


On Thursday, January 20, 2022 at 2:36:57 AM UTC-8 S Ling wrote:

> Hi Nick,
>
> If you read the original paper of ADMM (
> https://pubs.acs.org/doi/10.1021/ct1002225 ), they mentioned "the 
> condition number of the overlap matrix with the FIT3 basis is unfavorable 
> in the case of bulk C", see section 3.6. They produced a separate optFIT3 
> basis for C with much more favourable condition number. Unfortunately, I 
> cannot find the optFIT3 basis for C. I have personally produced an optFIT3 
> basis for B if you want to try.
>
> SL
>
> #####
>
> B OPTFIT3
>
> 6
>
> 1 0 0 1 1
>
>          0.27763115800007     1.00000000000000E+00
>
> 1 0 0 1 1
>
>          3.17679618980955     1.00000000000000E+00
>
> 1 0 0 1 1
>
>          8.21086367916339     1.00000000000000E+00
>
> 1 1 1 1 1
>
>          0.15104423596280     1.00000000000000E+00
>
> 1 1 1 1 1
>
>          0.61295240465023     1.00000000000000E+00
>
> 1 1 1 1 1
>
>          2.56244918405309     1.00000000000000E+00
>
> ##### 
>
> On Thu, 20 Jan 2022 at 03:24, Nicholas Winner <nwi... at berkeley.edu> wrote:
>
>> I've been looking at a couple of systems that are atomically pretty 
>> dense. For example, alpha boron and diamond.
>>
>> For these systems, when I increase the supercell size too large, the 
>> energy in the SCF loop explodes to ridiculous values. For example, I am 
>> calculating diamond with 54 atom and 128 atom supercells, truncated PBE0 
>> with 2A cutoff. 
>>
>> The 54 atom case converges with no real issues. In that case I have used 
>> OT, and against common wisdom for really accurate results I screen on the 
>> initial density matrix with scf_guess atomic. The convergence seems robust 
>> to that and the aggressive (1e-6) integral screening.
>>
>> Then, I move to 128 atom supercells, and I am unable to converge as the 
>> energies diverge rapidly after a few SCF steps. For this case, I have 
>> stopped screening on the initial density matrix. I was able to narrow the 
>> issue down to the auxiliary basis sets used for C. I tried cFIT3, pFIT3, 
>> cpFIT3, and FIT3, which all result in the rapid divergence of the energy. 
>> Example:
>>
>>
>>      1 OT CG       0.15E+00  141.5     0.01764397      -673.6622732538 
>> -6.74E+02
>>
>>      2 OT LS       0.60E+00   35.1                     -806.4853195301
>>
>>      3 OT CG       0.60E+00   38.5    12.03779293     -4186.8334161380 
>> -3.51E+03
>>
>>      4 OT LS       0.30E+00   33.7                    -8657.0632214970
>>
>> Since these all failed, but the primary basis is prohibitively large, I 
>> tried setting BASIS_SET AUX_FIT SZV-MOLOPT-SR-GTH, and this remedies the 
>> problem, and the calculation finishes.
>>
>> My questions then are four-fold.
>> (1) Is this behavior for dense systems like diamond expected? I have not 
>> had this issue with any other system besides alpha boron.
>> (2) Is this un-fixable? i.e. we can't use the FIT basis sets for such 
>> systems?
>> (3) Would someone have another idea for why this is the case? i.e. maybe 
>> FIT basis sets can still be used if some other setting was changed. 
>> and finally (4) Does anyone see an issue with proceeding with using the 
>> SZV basis as the auxiliary basis?
>>
>> -Nick
>>
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>>
>

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