How to set multigrid cutoff for GAPW?

[Nicholas Winner]

I know there is a well defined way for setting CUTOFF in the multigrid for GPW. Following Lippert's paper (https://link.springer.com/article/10.1007/s002140050523), we can take the relative cutoff and multiply it by the maximum exponent in the basis set.

That seems like the wrong strategy for the all electron basis sets, which can have exponents over 10,000.

Is there a scheme for setting the cutoff in GAPW, and is there a reference like Lippert's paper that can help understand that scheme?

Thanks,

Nick

[Marcella Iannuzzi]

Dear Nick

You could apply  the same scheme by considering the max exponent of the soft basis set. 

Kind regards

Marcella

[Jürg Hutter]

Hi

the soft basis set (printed out with MEDIUM) is used for the GPW grid part.
Typically, the max exponent of the soft basis is in the range of 5-8.

regards
JH

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Sent: Tuesday, December 13, 2022 11:47 PM
To: cp2k
Subject: [CP2K:18191] How to set multigrid cutoff for GAPW?

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[Nicholas Winner]

Thanks Jurg and Marcella. I ran a few tests and it looks like with the defaults all the exponents are pretty small (e.g. <5). 

How does EPSFIT used to determine the exponent cutoff? I read through some cp2k tutorial slides and all the ones I found say that the exponents are mapped, but not what the criteria exactly is.

[Jürg Hutter]

Hi

the maxiumum exponent included in the soft basis is:

zet = gauss_exponent(lshell, rc_hard, eps_fit, 1.0_dp)

where rc_hard is the "hard" radius of the atom "HARD_EXP_RADIUS".

It is the exponent that leads to a functional value of eps_fit at a distance of
rc_hard from the atom.

regards
JH

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From: cp...@googlegroups.com <cp...@googlegroups.com> on behalf of Nicholas Winner <nwi...@berkeley.edu>

Sent: Wednesday, December 14, 2022 9:10 PM
To: cp2k
Subject: Re: [CP2K:18205] How to set multigrid cutoff for GAPW?

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[Nicholas Winner]

Thanks Professor! I see the function in ao_utils.F and it makes sense now.