[Wien] Wien post from pascal.boulet at univ-amu.fr (Errors with DGEMM and hybrid calculations)

[Tran, Fabien]

> ​If I remember right, lmaxv & lmaxe change how the LM expansion is done inside the spheres, so need to be larger with higher L. The CPU scales something like a square, and they are CPU expensive.

Yes, in principle they should be increased (in particular lmaxv for open f-shells). In the Hartree-Fock expressions for energy and potential, there is a quadruple sums over lmaxv and a single sum over lmaxe.
 
> GMAX is a plane wave expansion, so (like lapw0) would need to be larger for small RMT such as H or odd cases. Again something like a square dependence, although I am not sure how CPU expensive except for a surface.

Yes.

> The CPU time will scale something like the product of the outer k-mesh and the inner (for which a reduced mesh can be used). Standard accuracy issue.

Yes.

> NBand in case.inhf is I think linear in CPU; I am not exactly sure why it needs to be larger than the number of occupied bands (forgotten).

Like spin-orbit coupling, HF/hybrid is implemented in a 2nd variational procedure. NBand orbitals from lapw1 are used as basis functions to construct a NBand*NBand Hamiltonian.

> RKMAX is standard, with a 2-3 power dependence of CPU time.

Maybe.

> N.B., I think there is also a dependence upon how different the straight lapw1 & hf are, for instance the band gap in lapw1. This matters for how large the number of states used in lapw1 has to be.

I don't understand.

_____
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu 


On Sat, Aug 15, 2020, 08:38 Tran, Fabien <fabien.tran at tuwien.ac.at> wrote:
  That's difficult since it may depend on the system, RMT, property, and required accuracy, but roughly (concerning  the parameters in case.inhf):

-For geometry: none of the parameters really need to be increased compared to default. In particular, nband can be set to minimum required (number of occupied bands plus one). Maybe gmax (from case.inhf) should be tested if RMT are chosen clearly smaller than  default. The option "-nonself" could also be used for non-magnetic systems.

-For cohesive energy: preferably test nband, gmax, lmaxe and lmaxv. Especially the latter two for systems with an open  f-shell.

-For electronic structure: test lmaxe and lmaxv for systems with an open  f-shell. For the band gap of non-magnetic systems, the option "-diaghf" (https://urldefense.com/v3/__https://doi.org/10.1016/j.physleta.2012.01.022__;!!Dq0X2DkFhyF93HkjWTBQKhk!AN3JSEcq-L36m1Ickxc1xjixv8KB9lE8fbCvyAvgSj7ySnH9QhVXJB8tDGGm-rjxGqJUjQ$  ) can be used to reduce the computational time by two orders of magnitude.

-For electron density (e.g., for EFG): Test carefully all parameters.

-k-mesh: In general, the convergence of properties with HF/hybrids is slower than with LDA/GGA/MGGA (fortunately only slightly slower with screened hybrids like HSE06).

-RKmax: the convergence is the same as for LDA/GGA/MGGA.

-Computational time: strongly influenced by k-mesh, RKmax, nband, lmaxe and lmaxv. Less by gmax (from case.inhf).


From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of Laurence Marks <laurence.marks at gmail.com>
Sent: Saturday, August 15, 2020 2:40 PM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] Wien post from  pascal.boulet at univ-amu.fr (Errors with DGEMM and hybrid calculations)
  
It would be good to have a brief summary of what matters with hf:
a) For speed
b) For accuracy

It is probably somewhere in the docu, but another cite for the list would be useful (to me as well as others).
_____
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody else has thought", Albert Szent-Gyorgi
http://www.numis.northwestern.edu
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