Dear Hongsheng, I don't understand why I should use relax instead of vc-relax. As far as I understand, when a system is under pressure, both the atomic positions inside a unit cell, as well as the dimensions of the unit cell changes. So, why should I keep the unit cell parameters fixed if I am interested in finding phase transitions?
Thanks On Mon, Jul 18, 2011 at 4:04 AM, Hongsheng Zhao <zhaohscas at yahoo.com.cn>wrote: > On 07/18/2011 09:40 AM, Amin Torabi wrote: > > Dear experts! > > > > Forgive me for my naive question... but I am interested in > > pressure-induced phase transitions of diborane. Could you please have a > > look at my input file, attached to this message. > > > > The following is what I think I should do: (correct me if I'm wrong!) > > > > 1. doing separate vc-relax calculation at each pressure > > By using this method, there are some limitations. You should have known > in advance the different phases between them the phase transition maybe > occur when we change the pressure. Then you can use this method to > determine the phase transition path. But I'm not so sure this method > can predict all of the possible phases for a system when we change the > external pressure. To do a more reasonable and complete phase > transition prediction and even searching for unknown phases, you should > use some third-party code like uspex for this type of job. > > In addition, I think you should do relax, not vc-relax calculation at > each pressure. If you do vc-relax, then the pressure imposed to the > system will be released. So you won't get the *Pressure-induced* phase > transition. > > > 2. comparing the optimized cell_parameters at each pressure to see when > > the structure changes > > > > I am wondering how I can use the enthalpy or unit cell volume at each > > pressure to make sure that a phase transition has occurred > > For the other questions, see this thread on this list: About the method > to obtain the common tangent for determing the phase transition > pressure. HTH. > > Regards > > > > Thanks in advance > > > > > > -- > > Amin Torabi > > Ph.D. Student > > Chemistry Department > > /The/ University /of/ Western Ontario > > London, On Canada, N6A 5B7 > > Phone: 519-661-2111 Ext: 87871 > > **************************************** > > > > > > > > _______________________________________________ > > Pw_forum mailing list > > Pw_forum at pwscf.org > > http://www.democritos.it/mailman/listinfo/pw_forum > > > -- > Hongsheng Zhao <zhaohscas at yahoo.com.cn> > School of Physics and Electrical Information Science, > Ningxia University, Yinchuan 750021, China > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- Amin Torabi Ph.D. Student Chemistry Department *The* University *of* Western Ontario London, On Canada, N6A 5B7 Phone: 519-661-2111 Ext: 87871 **************************************** -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110718/44c4d3e2/attachment-0001.htm