Dear Laurence Marks Sir,<div><br></div><div> 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?<br>
<br><div class="gmail_quote">On Wed, Feb 24, 2010 at 7:26 PM, Laurence Marks <span dir="ltr"><<a href="mailto:L-marks@northwestern.edu">L-marks@northwestern.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Unless something has changed, forces are not implemented for<br>
spin-orbit correctly so you cannot do a force minimization with them<br>
(unless you do some tricks, i.e. minimize the enegy by hand not using<br>
the code).<br>
<br>
For spin/U the question is how large a difference does this make to<br>
the electron density -- if it is large then the positions/optimal<br>
volume will be very different.<br>
<br>
But...do not depair! If spin-polarized and U is a much better<br>
description of the physics and you do not have multiple magnetic<br>
states, convergence of a LDA+U (or GGA+U) calculation can be much<br>
faster than a LDA calculation which does not describe the physics<br>
well. This follows from the physics/math of mixing.<br>
<br>
N.B., this is also why using a small mixing term in a<br>
Broyden/Multisecant method does not do what most people think it does,<br>
conventional wisdom is incorrect or at most correct for Pratt mixing.<br>
(Also, large mixing terms do not do what people think they do!) In<br>
general this not the way to solve a badly convergent problem, the<br>
correct (only) solution is to improve the physical model.<br>
<br>
2010/2/24 shamik chakrabarti <<a href="mailto:shamikphy@gmail.com">shamikphy@gmail.com</a>>:<br>
<div><div></div><div class="h5">> Dear Wien2k users,<br>
> I have a question regarding volume optimization<br>
> and force minimization.<br>
> If I do volume optimization and force minimization for non magnetic<br>
> calculation and then use that optimized volume and structural coordinates as<br>
> input for the calculation of volume optimization and force minimization<br>
> including spin polarization, spin orbit coupling term and LDA+U term, then<br>
> whether I get the correct optimized values for both volume and coordinates<br>
> of the structure which really need those corrections?<br>
> If I want to do volume and coordinates optimization including those<br>
> correction terms from the begining then it will take a very long time. But<br>
> if we do the optimization using non magnetic calculation to reach closer to<br>
> the actual energy and force minima and then put those optimized structure<br>
> for non magnetic calculation for the optimization of the structure having<br>
> those corrections it may take lesser time to reach the actual minima. But<br>
> whether we really get actual minima in this way?<br>
> The above two questions actually are the same questions. I am very sorry for<br>
> that reapeating. Actually I want to make clear my intentions to the wien2k<br>
> users.<br>
> Thanks in advance.<br>
> regards,<br>
> Shamik Chakrabarti<br>
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><br>
><br>
<br>
<br>
<br>
--<br>
Laurence Marks<br>
Department of Materials Science and Engineering<br>
MSE Rm 2036 Cook Hall<br>
2220 N Campus Drive<br>
Northwestern University<br>
Evanston, IL 60208, USA<br>
Tel: (847) 491-3996 Fax: (847) 491-7820<br>
email: L-marks at northwestern dot edu<br>
Web: <a href="http://www.numis.northwestern.edu" target="_blank">www.numis.northwestern.edu</a><br>
Chair, Commission on Electron Crystallography of IUCR<br>
<a href="http://www.numis.northwestern.edu/" target="_blank">www.numis.northwestern.edu/</a><br>
Electron crystallography is the branch of science that uses electron<br>
scattering and imaging to study the structure of matter.<br>
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</blockquote></div><br></div>