ok but i have seen many papers that this B2 unstability due to some anaharmonic contributions or it may be due to band closing phenomenon can u explain this more correctly because i am doing calculation on transition metal carbides On Wed, Aug 24, 2011 at 9:01 PM, Mike Mehl <Michael.Mehl at nrl.navy.mil>wrote:
> ZnS, WC, and NiAs are the likeliest candidates, but not the only ones. > > The unstable B1 phonons lead to structures which relax to something > lower in energy than B1. Since all of your candidate structures have a > higher enthalpy than B1 at 130 GPa, it can't be one of those structures. > Hence, it's a different structure. > > It should be frowned upon to hype one's own publications, but if you look > at > > M. J. Mehl, G. L. W. Hart, and S. Curtarolo > Journal of Alloys and Compounds, 509, pp. 560-567 (2011) > > (http://www.sciencedirect.com/science/article/pii/S0925838810021225 or > http://arxiv.org/abs/1006.0236) > > There are examples of how you can find new structures from unstable > phonon modes. This case sounds simpler than IrV. > > It would, of course, help us if we knew which carbides you were working on. > > On 08/24/2011 10:35 AM, bhabya sahoo wrote: > > no i have calculated correctly because the convergence is good with > > higher k points > > second is that i have tested zns,wc,NiAs phase none of them have less > > enthalpy at 130 gpa > > other thing is that it is stable at above 250 gpa > > > > > > On Wed, Aug 24, 2011 at 7:38 PM, Mike Mehl <Michael.Mehl at nrl.navy.mil > > <mailto:Michael.Mehl at nrl.navy.mil>> wrote: > > > > If the B1 structure is unstable with respect to the B2 structure > above > > 130 GPa, but the B2 structure is dynamically unstable at and above > 130 > > GPa, there are two possible conclusions: > > > > 1) The phonons for the B2 structure were not calculated accurately, > or > > > > 2) There is a competing structure that is lower in enthalpy than B1 > or > > B2 at 130 GPa > > > > Without more information, no one can judge which conclusion is > correct, > > suggest remedies for 1), or possible structure for 2). > > > > > -- > Michael J. Mehl > Head, Center for Computational Materials Science > Naval Research Laboratory Code 6390 > Washington DC > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110824/fd8e37ab/attachment-0001.htm