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

[Peter Blaha]

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
>>>
>>>
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>>>  Wien at zeus.theochem.tuwien.ac.at
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> 
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-- 
-----------------------------------------
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
-----------------------------------------