[Wien] volume optimization and force minimization

[Laurence Marks]

No, you cannot compare energies with/without spin-orbit, they are
different physics. You could optimize the volume after adding it in
(not internal co-ordinates) and this would be reasonable to do.

2010/2/24 shamik chakrabarti <shamikphy at gmail.com>:
> Dear Laurence Marks Sir,
>                                      Thank you very much for your reply.
> What we can do then.....we optimize both volume and coordinates including
> spin polarization and GGA+U and take this as the optimized structure as far
> as the theory is concerned. Then we take that structure and run one scf
> including spin-orbit coupling too. If the energy is less than the minimum
> energy obtained in volume optimization we can go with spin-orbit coupling or
> otherwise not. But it may happen that the energy is less and the volume is
> different (I don't know how much effect spin-orbit coupling will have on the
> volume!!...atleast we have experience that spin polarization definitely
> effects volume) then which volume we should accept as our optimized volume?
>
> On Wed, Feb 24, 2010 at 7:26 PM, Laurence Marks <L-marks at northwestern.edu>
> wrote:
>>
>> Unless something has changed, forces are not implemented for
>> spin-orbit correctly so you cannot do a force minimization with them
>> (unless you do some tricks, i.e. minimize the enegy by hand not using
>> the code).
>>
>> For spin/U the question is how large a difference does this make to
>> the electron density -- if it is large then the positions/optimal
>> volume will be very different.
>>
>> But...do not depair! If spin-polarized and U is a much better
>> description of the physics and you do not have multiple magnetic
>> states, convergence of a LDA+U (or GGA+U) calculation can be much
>> faster than a LDA calculation which does not describe the physics
>> well. This follows from the physics/math of mixing.
>>
>> N.B., this is also why using a small mixing term in a
>> Broyden/Multisecant method does not do what most people think it does,
>> conventional wisdom is incorrect or at most correct for Pratt mixing.
>> (Also, large mixing terms do not do what people think they do!) In
>> general this not the way to solve a badly convergent problem, the
>> correct (only) solution is to improve the physical model.
>>
>> 2010/2/24 shamik chakrabarti <shamikphy at gmail.com>:
>> > Dear Wien2k users,
>> >                             I have a question regarding volume
>> > optimization
>> > and force minimization.
>> > If I do volume optimization and force minimization for non magnetic
>> > calculation and then use that optimized volume and structural
>> > coordinates as
>> > input for the calculation of volume optimization and force minimization
>> > including spin polarization, spin orbit coupling term and LDA+U term,
>> > then
>> > whether I get the correct optimized values for both volume and
>> > coordinates
>> > of the structure which really need those corrections?
>> > If I want to do volume and coordinates optimization including those
>> > correction terms from the begining then it will take a very long time.
>> > But
>> > if we do the optimization using non magnetic calculation to reach closer
>> > to
>> > the actual energy and force minima and then put those optimized
>> > structure
>> > for non magnetic calculation for the optimization of the structure
>> > having
>> > those corrections it may take lesser time to reach the actual minima.
>> > But
>> > whether we really get actual minima in this way?
>> > The above two questions actually are the same questions. I am very sorry
>> > for
>> > that reapeating. Actually I want to make clear my intentions to the
>> > wien2k
>> > users.
>> > Thanks in advance.
>> > regards,
>> > Shamik Chakrabarti
>> > _______________________________________________
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>> > 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 and imaging to study the structure of matter.
>> _______________________________________________
>> Wien mailing list
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>
>
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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 and imaging to study the structure of matter.