[Wien] Mixer surprise when using PBE0 hybrid on-site functional
Laurence Marks
L-marks at northwestern.edu
Fri Jan 20 22:16:28 CET 2017
I can provide some partial responses, although there are also some things
that I don't understand. Some of this (maybe most) is not the mixer but in
other parts of Wien2k.
First, the old (2008) version is there if you use MSEC1, but I have not
tested it and it may fail. Better is to use MSEC3 which is almost the old
version. For some classes of problems this is more stable than MSR1, and
works better. If you are talking about the pre-multisecant version (BROYD)
that vanished some time ago.
Second, there is a nasty "feature" particularly for +U (eece) cases, which
is partially discussed in the mixer Readme. There is no guarantee that a
solution exists -- the KS theorem is for densities but U is an orbital
term. It is very possible to have cases where there is no fixed-point
solution. The older MSEC1 (maybe BROYD) could find a fake solution where
the density was consistent but the orbital potential was not. The latest
version is much better in avoiding them and going for "real" solutions
rather than being trapped. For orbital potentials it is very important to
look at :MV to check that one really has a self-consistent orbital
potential.
Third, there are cases where PBE (and all the GGA's in Wien2k that I have
tested) give unphysical results when applied to isolated d or f electrons
as done for -eece. I guess that the GGA functionals were not designed for
the densities of just high L orbitals. This leads to very bad behavior of
the mixing. I know of no way to solve this in the mixer, it is a structural
problem. It goes away if LDA is used as the form for VXC in -eece.
Fourth, larger problem with low symmetry (P1 in particular) can certainly
behave badly. Part of this might be "somewhere" in Wien2k coding, part of
it is generic to a low symmetry problem. In many cases these have small
eigenvalues in the mixing Jacobian which are removed when symmetry is
imposed. All one can do is use MSEC3 or some of the additional flags (see
the mixer README) such as "SLOW".
Fifth...probably exists, but I can't think of it immediately.
On Fri, Jan 20, 2017 at 2:03 PM, Xavier Rocquefelte <
xavier.rocquefelte at univ-rennes1.fr> wrote:
> Dear Colleagues
>
> I did recently a calculation which has been published long time ago
> using a old WIEN2k version (in 2008).
>
> It corresponds to a spin-polarized calculation for the compound CuO. The
> symmetry is removed and the idea is to estimate the total energies for
> different magnetic orders to extract magnetic couplings from a mapping
> analysis. Such calculations were converging fastly without any trouble
> in 2008.
>
> Here I have started from the scratch with a case.cif file to generate
> the case.struct file and initializing the calculation in a standard manner.
>
> Then I wanted to have the energy related to a ferromagnetic situation
> (not the more stable). I have 8 copper sites in the unit cell I am using.
>
> When this calculation is done using PBE+U everything goes fine. However
> when PBE0 hybrid on-site functional is used we observed oscillations and
> the magnetic moment disappear, which is definitely not correct. It
> should be mentionned that the convergency is really bad. If we do a
> similar calculation on the cristallographic unit cell (2 copper sites
> only) the calculations converge both in PBE+U and PBE0.
>
> The convergency problems only arises for low-symmetry and high number of
> magnetic elements. I didn't have such problems before and I wonder if we
> could still use old mixer scheme in such situations. Looking at the
> userguide, it seems that the mixer does not allow to do as before and
> PRATT mixer is too slow.
>
> Did you encounter similar difficulties (which were not in older WIEN2k
> versions)?
>
> Best Regards
>
> Xavier
>
> Here is the case.struct:
>
> blebleble
> P LATTICE,NONEQUIV.ATOMS: 16 1_P1
> MODE OF CALC=RELA unit=bohr
> 14.167163 6.467777 11.993298 90.000000 95.267000 90.000000
> ATOM -1: X=0.87500000 Y=0.75000000 Z=0.87500000
> MULT= 1 ISPLIT= 8
> Cu NPT= 781 R0=0.00005000 RMT= 1.9700 Z: 29.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -2: X=0.12500000 Y=0.25000000 Z=0.62500000
> MULT= 1 ISPLIT= 8
> Cu NPT= 781 R0=0.00005000 RMT= 1.9700 Z: 29.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -3: X=0.12500000 Y=0.25000000 Z=0.12500000
> MULT= 1 ISPLIT= 8
> Cu NPT= 781 R0=0.00005000 RMT= 1.9700 Z: 29.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -4: X=0.87500000 Y=0.75000000 Z=0.37500000
> MULT= 1 ISPLIT= 8
> Cu NPT= 781 R0=0.00005000 RMT= 1.9700 Z: 29.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -5: X=0.62500000 Y=0.25000000 Z=0.62500000
> MULT= 1 ISPLIT= 8
> Cu NPT= 781 R0=0.00005000 RMT= 1.9700 Z: 29.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -6: X=0.37500000 Y=0.75000000 Z=0.87500000
> MULT= 1 ISPLIT= 8
> Cu NPT= 781 R0=0.00005000 RMT= 1.9700 Z: 29.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -7: X=0.37500000 Y=0.75000000 Z=0.37500000
> MULT= 1 ISPLIT= 8
> Cu NPT= 781 R0=0.00005000 RMT= 1.9700 Z: 29.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -8: X=0.62500000 Y=0.25000000 Z=0.12500000
> MULT= 1 ISPLIT= 8
> Cu NPT= 781 R0=0.00005000 RMT= 1.9700 Z: 29.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -9: X=0.87500000 Y=0.41840000 Z=0.62500000
> MULT= 1 ISPLIT= 8
> O NPT= 781 R0=0.00010000 RMT= 1.6900 Z: 8.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -10: X=0.12500000 Y=0.91840000 Z=0.87500000
> MULT= 1 ISPLIT= 8
> O NPT= 781 R0=0.00010000 RMT= 1.6900 Z: 8.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -11: X=0.12500000 Y=0.58160000 Z=0.37500000
> MULT= 1 ISPLIT= 8
> O NPT= 781 R0=0.00010000 RMT= 1.6900 Z: 8.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -12: X=0.87500000 Y=0.08160000 Z=0.12500000
> MULT= 1 ISPLIT= 8
> O NPT= 781 R0=0.00010000 RMT= 1.6900 Z: 8.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -13: X=0.62500000 Y=0.58160000 Z=0.87500000
> MULT= 1 ISPLIT= 8
> O NPT= 781 R0=0.00010000 RMT= 1.6900 Z: 8.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -14: X=0.37500000 Y=0.08160000 Z=0.62500000
> MULT= 1 ISPLIT= 8
> O NPT= 781 R0=0.00010000 RMT= 1.6900 Z: 8.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -15: X=0.37500000 Y=0.41840000 Z=0.12500000
> MULT= 1 ISPLIT= 8
> O NPT= 781 R0=0.00010000 RMT= 1.6900 Z: 8.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -16: X=0.62500000 Y=0.91840000 Z=0.37500000
> MULT= 1 ISPLIT= 8
> O NPT= 781 R0=0.00010000 RMT= 1.6900 Z: 8.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> 1 NUMBER OF SYMMETRY OPERATIONS
> 1 0 0 0.00000000
> 0 1 0 0.00000000
> 0 0 1 0.00000000
> 1
>
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--
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 ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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