[Wien] O2 molecule continue (rmt issue)

[Laurence Marks]

N.N.B., instead of a smaller ecut one can use .lcore. Sometimes this also
improves convergence.

_____
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 Nov 13, 2017 2:12 PM, "Laurence Marks" <L-marks at northwestern.edu> wrote:

> "besides the statement: be careful with the energy parameter (very fine
> E-search in case.in1)"
> N.B., one does not need a fine search in the more recent Wien2k, only in
> the older versions.
>
> I seem to remember that GMax 20 mainly cancels out for LDA/GGA -- I would
> always use it (or more) for a meta GGA.
>
> _____
> 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 Nov 13, 2017 2:00 PM, "Peter Blaha" <pblaha at theochem.tuwien.ac.at>
> wrote:
>
> > 1- Computing the atomic energies of atoms like N and P in an FCC cell is
> > ok, however for O atom the high symmetry of the FCC cell results in 1/3
> > occupancies (for the 4th p electron of O) in the spin down case. Only
> > using a lower symmetry cell (orthorhombic) for O atom eliminates this
> issue.
>
> This is true, however, for O this is a very small (negligible) energy
> difference. It is a bit more important (also to help convergence) for
> transition metals or even lanthanides.
>
> > 2- For very small RMTs (e.g. 1.1 for O) one needs a large value of Gmax
> > (~20).
>
> Again true. GMAX for small spheres has some effect on E-tot. I have not
> cross checked if this truncation cancels out in the energy differences.
>
> > Using RMT = 1.1 for O in a compound will require one to use too small
> > RMTs for large atoms. For example if we use RMT = 1.1 for O in compounds
> > like SnO2, this will require one to use an RMT ~ 1.6 for Sn (RMTs
> > difference should not be > 30 %). This means that the ecut should be set
> > < -9.8 Ry which includes the 4s electrons to valence states. What are
> > the consequences?
>
> Without test: I would "break" my own rules and set the Sn sphere still
> to 2.0 or 2.2 (such that no core leakage occurs at ecut=-6). I would not
> expect ghostbands coming up. This rule usually applies to cases where
> one atom could have very large RMT (2.5 or even larger) and probably
> converges rapidly (eg. alkali(earth) atoms in TM perovskites, ...)
>
> But in principle there is nothing to say against Sn 4s as valence,
> besides the statement: be careful with the energy parameter (very fine
> E-search in case.in1) and make sure that RKmax is sufficient for such
> localized states.
>
>
> >
> > Best Regards,
> >
> > Alay
> >
> >
> >
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> --
> --------------------------------------------------------------------------
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