Re: [Wien] When to use (or not) onsite hybrid or +U?

2021-07-04 Thread Laurence Marks 
I will argue that there are two ways to interpret hybrids/+U:
a) As corrections for localized, higher angular momentum states which are
poorly modelling by standard functionals based upon slowly varying density.
b) Corrections in the spirit of Slater-Janek, such that the energy of the
states (d/f) is independent of small variations.

For a) one can fit, if available, using thermodynamic data or atomic
positions. For b) one can fit an insulator as described in the notes, but
only for +U . One can perhaps fit to a full hybrid, but then this is
fitting to a fit!

It would be nice to have a "b" for -eece. I can think about using an
isolated atom, since maybe the fraction is transferrable...
--
On Sat, Jul 3, 2021 at 12:05 PM Peter Blaha 
wrote:

> No, I would not use DFT+U or onsite-hybrids for a metallic Mo (4d !!)
> SiB compound. The 4 d states are not localized enough.
>
> I'd use SCAN for energetics, and maybe check for effects using a vdW
> functional (depends on the compound and structure).
>
> Am 03.07.2021 um 16:30 schrieb Laurence Marks:
> > Are there ways to test/calibrate what onsite hybrid or +U to use for
> > metals (i.e. compounds with states at EF)?
> >
> > For context, I am doing some test calculations for Mo-Si-B compounds,
> > currently using PBE without spin. From my analysis of the energies there
> > are some Mo-B compounds which can be found in the ICSD database, but are
> > marginal in terms of the heat of formation and are not in
> > published phase diagrams. Unfortunately the phase diagram work to date
> > has not used the most modern characterization methods, so it may be
> > incomplete. IMHO if a structure/composition is in ICSD it should be real.
> >
> > I know one way to calibrate on-site fractions is matching experimental
> > atomic positions, but none of these appear to be good enough (there are
> > fractional occupancies in some cases). Obviously matching band-gaps is
> > useless, even if I believed in this (which I don't).
> >
> > Any suggestions?
> >
> > --
> > Professor Laurence Marks
> > Department of Materials Science and Engineering
> > Northwestern University
> > http://www.numis.northwestern.edu 
> > "Research is to see what everybody else has seen, and to think what
> > nobody else has thought" Albert Szent-Györgyi
> >
> > ___
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> >
>
> --
> --
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
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>


-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
"Research is to see what everybody else has seen, and to think what nobody
else has thought" Albert Szent-Györgyi
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Re: [Wien] When to use (or not) onsite hybrid or +U?

2021-07-03 Thread Peter Blaha 
No, I would not use DFT+U or onsite-hybrids for a metallic Mo (4d !!) 
SiB compound. The 4 d states are not localized enough.


I'd use SCAN for energetics, and maybe check for effects using a vdW 
functional (depends on the compound and structure).


Am 03.07.2021 um 16:30 schrieb Laurence Marks:
Are there ways to test/calibrate what onsite hybrid or +U to use for 
metals (i.e. compounds with states at EF)?


For context, I am doing some test calculations for Mo-Si-B compounds, 
currently using PBE without spin. From my analysis of the energies there 
are some Mo-B compounds which can be found in the ICSD database, but are 
marginal in terms of the heat of formation and are not in 
published phase diagrams. Unfortunately the phase diagram work to date 
has not used the most modern characterization methods, so it may be 
incomplete. IMHO if a structure/composition is in ICSD it should be real.


I know one way to calibrate on-site fractions is matching experimental 
atomic positions, but none of these appear to be good enough (there are 
fractional occupancies in some cases). Obviously matching band-gaps is 
useless, even if I believed in this (which I don't).


Any suggestions?

--
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu 
"Research is to see what everybody else has seen, and to think what 
nobody else has thought" Albert Szent-Györgyi


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--
--
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
Email: bl...@theochem.tuwien.ac.atWIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at
-
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[Wien] When to use (or not) onsite hybrid or +U?

2021-07-03 Thread Laurence Marks 
Are there ways to test/calibrate what onsite hybrid or +U to use for metals
(i.e. compounds with states at EF)?

For context, I am doing some test calculations for Mo-Si-B compounds,
currently using PBE without spin. From my analysis of the energies there
are some Mo-B compounds which can be found in the ICSD database, but are
marginal in terms of the heat of formation and are not in published phase
diagrams. Unfortunately the phase diagram work to date has not used the
most modern characterization methods, so it may be incomplete. IMHO if a
structure/composition is in ICSD it should be real.

I know one way to calibrate on-site fractions is matching experimental
atomic positions, but none of these appear to be good enough (there are
fractional occupancies in some cases). Obviously matching band-gaps is
useless, even if I believed in this (which I don't).

Any suggestions?

-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
"Research is to see what everybody else has seen, and to think what nobody
else has thought" Albert Szent-Györgyi
___
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http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
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