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

[Laurence Marks]

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
>
>
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-- 
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.