[Wien] volume optimization and force minimization

[Laurence Marks]

Sorry, I am not an expert on Fe although I think you only want
spin-orbit for heavy atoms.

2010/2/24 shamik chakrabarti <shamikphy at gmail.com>:
> Dear Laurence Marks Sir,
>                                      We are doing calculation on a system
> which has Fe atom as the most atomic numbered atom. Other atoms have less
> atomic no. than Fe. Then is it really necessary to include spin orbit
> coupling term for this system?....otherwise we can exclude it and do the
> necessary optimization.
> Another question is....is this spin-orbit coupling term can have any effect
> on volume or internal coordinates?
> Sir....till now I have got lots of information from you. I am very greatfull
> to you sir for all your replies.
> Thanking You,
> with regards,
> Shamik Chakrabarti
>
> On Wed, Feb 24, 2010 at 10:34 PM, Laurence Marks <L-marks at northwestern.edu>
> wrote:
>>
>> 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
>> >> > _______________________________________________
>> >> > Wien mailing list
>> >> > 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.
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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.
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
>
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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.