[Wien] total energy when using -orbc for constant V-matrix

[Laurence Marks]

This would add back the relevant terms, but I think there is another
problem. There is nothing constraining your d (or f) occupancies, so
these will vary and you may get a very inconsistent (unphysical)
solution. You may be able to force a solution by fixing your dmat by
hand, calculating orb with this and then running as Peter suggested
but nothing forces the final dmat to be what you want/think it should
be. You will have to check that the dmat in the iterations is close to
what you wanted it to be, otherwise everything will be GIGO.

On Fri, May 15, 2009 at 10:47 AM, Peter Blaha
<pblaha at theochem.tuwien.ac.at> wrote:
> Just a guess, it might work:
>
> Try    runsp -orb    (not -orbc !), but change the PRATT factor in
> case.inorb to 0.0
>
> I expect that will run orb and the Eorb total energy contribution will
> be added, but it will not update case.vorbup/dn.
>
> Please let me know if it works.
>
> Hua Wu schrieb:
>> Dear Stefaan Cottenier and Laurence Marks,
>>
>>   Thanks a lot for your prompt replies and the useful information.
>>
>>  May I understand your points as follows:  The U-related part of total energy
>> is not taken into account when using -orbc, since -orbc fixes the orbital
>> potential and thus the calculations skip the nomal 'x -orb -up/dn' where the
>> U-related part of total energy is calculated.
>>
>>  My further question is: can I regard the 'converged' total energy and forces
>> calculated using -orbc as a quasi LDA/GGA result WITHIN the constrained
>> orbital polarization?  If so, I may still be able to do structural
>> relaxations using -orbc, e.g, to see (maybe roughly) how a lattice responds
>> to the constrained orbital states (which can not be stabilized when
>> using -orb).
>>
>> best regards -- H. Wu
>>
>>
>> On Friday 15 May 2009 15:56, Laurence Marks wrote:
>>> I'm fairly certain that with -orbc you are not including the
>>> double-counting corrections which are normally calculated with x orb
>>> -up/dn, hence large apparent changes.
>>>
>>> On 5/15/09, Stefaan Cottenier <Stefaan.Cottenier at ugent.be> wrote:
>>>>  >   I tried to use LDA+U with -orbc flag to stabilize various orbital
>>>>  > polarized states in my calculations for some transition-metal oxides.
>>>>  > In order to compare their total energies, I made a simple test,
>>>>  > namely, run 'LDA+U with -orbc' for a well converged 'LDA+U with -orb'
>>>>  > case. The total energies are expected to be the same. However,  it is
>>>>  > surprising that in my current calculations using the latest version,
>>>>  > the total energies change by several Rydbergs. I am wondering if any
>>>>  > term is missing in the calculations of the total energy when using
>>>>  > -orbc. In addition, can one use -orbc to do structural relaxation like
>>>>  > doing LDA+U with -orb ?
>>>>
>>>> -orbc is not meant for 'final' calculations, but rather for bringing the
>>>>  scf cycle close to a type of solution you want. Then you turn off -orbc
>>>>  (i.e. use plain -orb), after which the scf cycle will spontaneously
>>>>  stabilize in the nearest local energy minimum, which can (but not always
>>>>  should) have the qualitative properties of the solution you wanted to
>>>>  enforce.
>>>>
>>>>  I did notice indeed that when used that way, there are several Ry's of
>>>>  difference between energies with and without -orbc. I cannot give you
>>>>  the technical explanation for this (others ?), but never cared about it
>>>>  as I always use the energies with plain -orb anyway.
>>>>
>>>>  Note: -orbc freezes the orbital potential that is consistent with the
>>>>  initial density matrices. It does not freeze the density matrices
>>>>  themselves: they can evolve during the scf cycle. Hence, when using
>>>>  -orbc as described above, you better check at the end of the -orbc scf
>>>>  cycle whether the final density matrices are not too different from your
>>>>  initial ones. If they are very different, you probably did not end up
>>>>  close the type of solution you wanted to enforce, and the subsequent
>>>>  -orb scf cycle might result into a selfconsistent solution that you do
>>>>  not want.
>>>>
>>>>
>>>>  Stefaan
>>>>
>>>>
>>>>  _______________________________________________
>>>>  Wien mailing list
>>>>  Wien at zeus.theochem.tuwien.ac.at
>>>>  http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
> --
> -----------------------------------------
> Peter Blaha
> Inst. Materials Chemistry, TU Vienna
> Getreidemarkt 9, A-1060 Vienna, Austria
> Tel: +43-1-5880115671
> Fax: +43-1-5880115698
> email: pblaha at theochem.tuwien.ac.at
> -----------------------------------------
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>



-- 
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60208, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
Web: www.numis.northwestern.edu
Chair, Commission on Electron Crystallography of IUCR
www.numis.northwestern.edu/
Electron crystallography is the branch of science that uses electron
scattering to study the structure of matter.