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

[Pavel Novak]

Dear colleagues,

using constant orbital potential is equivalent to using external 
potential, which is different for different |m_l,m_s> states (similarly as 
external magnetic field brings different energy for different m_s). 
The total energy may be easily corrected by multiplying the orbital 
potential by corresponding population (density) matrix. This is not 
implemented in WIEN and I do it by separate small program. It might be 
worth to add this option to present WIEN version.

Regards
Pavel 

On Fri, 15 May 2009, 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
> >
> >
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> >
> 
> 
> 

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