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scf.Ngrid estimate
Date: 2020/03/30 20:07
Name: Luca Sementa

Dear Developers

Which way one can estimate the scf.Ngrid parameters to use when making a cell relaxation?
Is there a file where the code prints the employed plane-wave grid?

Best Regards.

Luca
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Re: scf.Ngrid estimate ( No.1 )
Date: 2020/03/31 02:22
Name: Naoya Yamaguchi

Hi,

You may refer to the following:
http://www.openmx-square.org/forum/patio.cgi?mode=view&no=1543

>Is there a file where the code prints the employed plane-wave grid?
A source file "truncation.c" outputs the used grid.
You can refer to the following part of "truncation.c" for estimation of the number of grids:
if (Ngrid_fixed_flag==0){

/* find proper N1, N2, and N3 */
(Omission)
}
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Re: scf.Ngrid estimate ( No.2 )
Date: 2020/03/31 11:16
Name: T. Ozaki

Hi,

Instead of scf.Ngrid, if you specify the following keyword:

scf.energycutoff 120.0

you may see, e.g., the following information in the standard output:

Required cutoff energy (Ryd) for 3D-grids = 120.0000
Used cutoff energy (Ryd) for 3D-grids = 113.2041, 113.2041, 113.2041
Num. of grids of a-, b-, and c-axes = 64, 64, 64

From the line: "Num. of grids of a-, b-, and c-axes = 64, 64, 64",
you can get the numbers of grids which nearly satisfy the required cutoff energy.
Starting from the numbers, you can modify a proper set of numbers.

If the cell volume charges largely during the cell relaxation, and you want to investigate
the energetics, you need to make sure that almost a same accuracy is achieved with respect to
the number of grids, which can be confirmed by looking the the cutoff energy in the standard output,
for all the optimized structures. Otherwise, your calculations may not be reliable.

Regards,

TO
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Re: scf.Ngrid estimate ( No.3 )
Date: 2020/04/02 03:14
Name: Luca Sementa

Dear Prof. Ozaki and dear Naoya

thank you for your answer!
Best Regards.
Luca
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