Hi Mohsen, I will try as you suggest and see if I can calculate the constants using the second derivative of energy.
All the best, Ben > Dear Ben, > If you think you are new in this topic, you need to study more > references. > As you said you have two specific ways. I only share my experience on > this subject. The first way is not applicable for super-cell model. > For example you can calculate the Youngs moduls of Graphene (which is > a 2D material) by using this method. by increasing/decreasing the > space between layers the elastic constant changes (which has not any > physical reason). So i suggest the second way. You could vc-relax the > structure, then deform it and relax by using "relax". By using the > second derivative of energy with respect to the strain Y is calculated. > Good luck. > > > On Fri, Nov 16, 2012 at 9:39 AM, Ben Palmer <benpalmer1983 at gmail.com > <mailto:benpalmer1983 at gmail.com>> wrote: > > Hi, > > I've read a number of forum posts about calculating elastic constants, > but I was hoping someone could give me some advice. (I'm trying to > calculate the elastic constants of bcc Iron). > > From what I have read, there are two ways I could do this: > > 1) Relax the unit cell with vc-relax, deform the cell (by about > 0.5-1%) > and relax internally with relax. I'd then have the stress tensor > of the > deformed cell. > > 2) Deform the relaxed cell at regular strain intervals, then fit a > polynomial to the strain-energy data. > > Am I right in saying I have those two options, or am I partly or > completely wrong? > > If I tried the first option, it's been said to calculate the elastic > constants from the strain-stress relationship. Would that mean > solving > the equation: > > Tij = Cijkl Ekl the ijkl are subscripts, T stress, E strain, C > stiffness tensor > > I'm fairly new to the subject so I could be quite wrong in what > I've said. > > Thanks > > Ben Palmer > Student @ University of Birmingham UK > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org> > http://pwscf.org/mailman/listinfo/pw_forum > > > > > -- > Mohsen Modarresi, > PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran. > Phone +98-9133452131 > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121116/855e9f55/attachment.html
