[Wien] volume optimization and force minimization

[shamik chakrabarti]

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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