[Pw_forum] LDA+U in md calculations

Matteo Cococcioni matteo at umn.edu
Mon Apr 5 05:36:35 CEST 2010

Dear Jiayu

in order to fully account the effects of the +U correction on pressure 
one should include a contribution from dU/dV too.
you may find this reference useful:

Phys. Rev. B 12, 125124 (2009)



Jiayu Dai wrote:
> Dear Matteo,
> Thanks for your comments. I am using the BOMD (pwscf). In my case, at high density, i would expect the U should be different with the change of ionic structures. In particular, i am concerning about the pressure. I found a strange thing: the pressure with LDA+U is lower than the pressure without U adding. As my experience, th pressure should be larger when we added the U parameter, is it right?
> Besides, all the cases using LDA+U is about the transition metals, which has the d or f electrons. How about the s or p electrons? 
> Thanks.
> Jiayu
> Dear Jiayu,
> are you talking about Car-Parrinello MD or Born-Oppenheimer MD (run with 
> pwscf)?
> In any case lda+U MD is implemented in the sense that the code computes 
> the forces and the stress
> as derivatives of  the lda+U energy functional. However it is not able 
> to account for the variation
> of U with atomic position or with the cell. So it is a dynamics at fixed U.
> To account for this variation one would need to evaluate dU/dR or 
> dU/d\epsilon (R and \epsilon being atomic
> positions and strains). Some work in this direction has been recently 
> done (not sure it's
> published yet) by Kulik and Marzari.
> If the structure you are interested in doesn't change dramatically 
> during the MD run I would expect
> that keeping the same U is not too bad. but this is just my guess.
> regards,
> Matteo
> Jiayu Dai wrote:
>> Dear developers,
>> I have some doubts about the molecular dynamics calculations using LDA+U. First, is LDA+U performed in MD calculations? Because i did not find the Hubbard energy in the output file of MD. Second, i think the value of U be dependent on the temperature and density, also on the ionic structures. Therefore, since ionic positions are different in each time step, is U different at each time step? If so, the performance of LDA+U should be very difficult in MD.
>> I did not know if what i said is right. Hope experts comment on this problem.
>> Thanks a lot.
>> Jiayu
>> -------------------------------------------
>> Jiayu Dai
>> Department of Physics
>> National University of Defense Technology, 
>> Changsha, 410073, P R China
>> -----------------------------------------
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Matteo Cococcioni
Department of Chemical Engineering and Materials Science,
University of Minnesota
421 Washington Av. SE
Minneapolis, MN 55455
Tel. +1 612 624 9056    Fax +1 612 626 7246

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