Dear Vega, --- On Fri, 8/29/08, vega <vegalew at hotmail.com> wrote:
> How could you get the relationship between the free > energy and volume? Do you mean that you changed the > cell volume sequentially and make a scf > calculation to gain the free energies for the certain > volume? the cell volume was grown bit by bit as > your will, then the scf calculation did accordingly? > We calculated total energy and phonons (then free energy) for a given set of volumes. > and how could you get the volume as a function of > pressure as fig.2 shown? > what kind of QE calculation could deal with it? > If you set up tstress=.true. you can find what is a stress (and pressure) in your system. Again, for a given set of the unit cell volumes. Sometime only a SCF calculation is enough, but sometime, especially for non-cubic systems, you can fix pressure and relax your system. Bests, Eyvaz. > vega > > -------------------------------------------------- > From: "Eyvaz Isaev" <eyvaz_isaev at yahoo.com> > Sent: Friday, August 29, 2008 9:00 PM > To: "PWSCF Forum" <pw_forum at pwscf.org> > Subject: Re: [Pw_forum] something strange in rutile and > anatase calculation > > > Dear Vega, > > > > > On the left side (under pressure) first DHCP has the > lowest energy, then > > hcp, and finally, FCC phase is the lowest in energy. > So, we stated, there > > are DHCP --> HCP and HCP --> FCC phase > transitons > > > > Hope this helps. > > > > Bests, > > Eyvaz > > > > > ------------------------------------------------------------------- > > Prof. Eyvaz Isaev, > > Theoretical Physics Department, Moscow State Institute > of Steel & Alloys, > > Russia, > > Department of Physics, Chemistry, and Biology (IFM), > Linkoping University, > > Sweden > > Condensed Matter Theory Group, Uppsala University, > Sweden > > Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, > eyvaz_isaev at yahoo.com > > > > > > --- On Thu, 8/28/08, vega <vegalew at hotmail.com> > wrote: > > > >> From: vega <vegalew at hotmail.com> > >> Subject: Re: [Pw_forum] something strange in > rutile and anatase > >> calculation > >> To: eyvaz_isaev at yahoo.com, "PWSCF Forum" > <pw_forum at pwscf.org> > >> Date: Thursday, August 28, 2008, 6:05 PM > >> Dear Eyvaz, > >> > >> I have read your PNAS paper just now. I'm very > >> interesting about the phase > >> transition mentioned in your paper. But because of > lack of > >> experience in > >> your scopes, I'm not very clear about the > detail of the > >> calculations of > >> phase transitions. > >> In the second paragraph of Results and Discussion > section, > >> you said > >> 'According to > >> our free-energy calculations, there exist two > phase > >> transitions in the FeH > >> system...'. How did you simulated the two > phase > >> transitions? How could you > >> calculate the Volume as a function of Pressure as > shown in > >> Fig. 2? The line > >> in Fig. 2 went quite smoothly, so you may not plot > it point > >> by point. How > >> could you get the line? > >> > >> thank you for reading > >> > >> vega > >> > >> > >> -------------------------------------------------- > >> From: "Eyvaz Isaev" > <eyvaz_isaev at yahoo.com> > >> Sent: Thursday, August 28, 2008 9:25 PM > >> To: "PWSCF Forum" > <pw_forum at pwscf.org> > >> Subject: Re: [Pw_forum] something strange in > rutile and > >> anatase calculation > >> > >> > Dear Vega, > >> > > >> > Please be not so official. I add > (automatically) my > >> affiliation due to our > >> > accepted Netetiquette. > >> > > >> > Bests, > >> > Eyvaz. > >> > > >> > > >> > ------------------------------------------------------------------- > >> > Prof. Eyvaz Isaev, > >> > Theoretical Physics Department, Moscow State > Institute > >> of Steel & Alloys, > >> > Russia, > >> > Department of Physics, Chemistry, and Biology > (IFM), > >> Linkoping University, > >> > Sweden > >> > Condensed Matter Theory Group, Uppsala > University, > >> Sweden > >> > Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, > >> eyvaz_isaev at yahoo.com > >> > > >> > > >> > --- On Thu, 8/28/08, vega > <vegalew at hotmail.com> > >> wrote: > >> > > >> >> From: vega <vegalew at hotmail.com> > >> >> Subject: Re: [Pw_forum] something strange > in > >> rutile and anatase > >> >> calculation > >> >> To: eyvaz_isaev at yahoo.com, "PWSCF > Forum" > >> <pw_forum at pwscf.org> > >> >> Date: Thursday, August 28, 2008, 5:08 PM > >> >> Thank you for Prof. Eyvaz Isaev's > hints > >> >> I'll read the excellent article as > your > >> suggestion. > >> >> It's really nice of you. > >> >> > >> >> vega > >> >> > >> >> > -------------------------------------------------- > >> >> From: "Eyvaz Isaev" > >> <eyvaz_isaev at yahoo.com> > >> >> Sent: Thursday, August 28, 2008 8:58 PM > >> >> To: "PWSCF Forum" > >> <pw_forum at pwscf.org> > >> >> Subject: Re: [Pw_forum] something strange > in > >> rutile and > >> >> anatase calculation > >> >> > >> >> > Hi, > >> >> > > >> >> > One more suggestion. > >> >> > As far as I know the same situation > is for > >> \alpha > >> >> and \omega phases of Ti, > >> >> > as well as HCP and DHCP phases of > FeH. But > >> free energy > >> >> calculations have > >> >> > shown than \alpha-Ti and DHCP > FeH are > >> stabilized > >> >> due to the phonon > >> >> > contribution. > >> >> > For FeH you can see: Eyvaz I. Isaev > et al., > >> Dynamical > >> >> stability of Fe-H in > >> >> > the Earth's mantle and core > regions, > >> Proceedings > >> >> of the National Academy > >> >> > of Sciences of the USA (PNAS), 104 > (22), 29 > >> May 2007, > >> >> 9168. PNAS Special > >> >> > Issue "Geophysics". > >> >> > > >> >> > So, you can try follow this way, if > you like. > >> >> > > >> >> > Bests, > >> >> > Eyvaz. > >> >> > > >> >> > > >> >> > > >> >> > >> > ------------------------------------------------------------------- > >> >> > Prof. Eyvaz Isaev, > >> >> > Theoretical Physics Department, > Moscow State > >> Institute > >> >> of Steel & Alloys, > >> >> > Russia, > >> >> > Department of Physics, Chemistry, > and Biology > >> (IFM), > >> >> Linkoping University, > >> >> > Sweden > >> >> > Condensed Matter Theory Group, > Uppsala > >> University, > >> >> Sweden > >> >> > Eyvaz.Isaev at fysik.uu.se, > isaev at ifm.liu.se, > >> >> eyvaz_isaev at yahoo.com > >> >> > > >> >> > > >> >> > --- On Thu, 8/28/08, Nicola Marzari > >> >> <marzari at MIT.EDU> wrote: > >> >> > > >> >> >> From: Nicola Marzari > >> <marzari at MIT.EDU> > >> >> >> Subject: Re: [Pw_forum] > something strange > >> in > >> >> rutile and anatase > >> >> >> calculation > >> >> >> To: "PWSCF Forum" > >> >> <pw_forum at pwscf.org> > >> >> >> Date: Thursday, August 28, 2008, > 3:01 PM > >> >> >> vega wrote: > >> >> >> > Dear all, > >> >> >> > > >> >> >> > It is known that the rutile > is more > >> stable > >> >> than > >> >> >> anatase in > >> >> >> > thermodynamics. > Surprisingly, when I > >> did the > >> >> vc-relax > >> >> >> calculation by > >> >> >> > QE, I found the calculated > energy of > >> anatase > >> >> lower > >> >> >> than rutile. Both > >> >> >> > vc-relax calculation for > rutile and > >> anatase > >> >> onverged > >> >> >> in 6 scf cycles and > >> >> >> > 3 bfgs steps, giving the > final > >> enthalpy = > >> >> >> -362.7585836890 Ry for rutile > >> >> >> > and -725.5447425835 Ry for > antase. > >> So the > >> >> average > >> >> >> energy of [TiO2] unit > >> >> >> > is -181.3792918445 Ry for > rutile and > >> >> -181.386185645875 > >> >> >> Ry for anatase. > >> >> >> > It looks like anatase is > more stable > >> than > >> >> rutile. Do > >> >> >> you think it was > >> >> >> > quite strange? > >> >> >> > >> >> >> > >> >> >> Dear Vega, > >> >> >> > >> >> >> your results are probably > correct. > >> It's a > >> >> known failure > >> >> >> of LDA and GGA > >> >> >> to stabilize anatase more than > rutile. > >> >> >> > >> >> >> nicola > >> >> >> > >> >> >> -- > >> >> >> > >> >> > >> > --------------------------------------------------------------------- > >> >> >> Prof Nicola Marzari Department > of > >> Materials > >> >> Science and > >> >> >> Engineering > >> >> >> 13-5066 MIT 77 Massachusetts > Avenue > >> >> Cambridge MA > >> >> >> 02139-4307 USA > >> >> >> tel 617.4522758 fax 2586534 > >> marzari at mit.edu > >> >> >> http://quasiamore.mit.edu > >> >> >> > >> _______________________________________________ > >> >> >> Pw_forum mailing list > >> >> >> Pw_forum at pwscf.org > >> >> >> > >> http://www.democritos.it/mailman/listinfo/pw_forum > >> >> > > >> >> > > >> >> > > >> >> > > >> _______________________________________________ > >> >> > Pw_forum mailing list > >> >> > Pw_forum at pwscf.org > >> >> > > >> http://www.democritos.it/mailman/listinfo/pw_forum > >> >> > > >> >> > _______________________________________________ > >> >> Pw_forum mailing list > >> >> Pw_forum at pwscf.org > >> >> > http://www.democritos.it/mailman/listinfo/pw_forum > >> > > >> > > >> > > >> > > _______________________________________________ > >> > Pw_forum mailing list > >> > Pw_forum at pwscf.org > >> > > http://www.democritos.it/mailman/listinfo/pw_forum > >> > > >> _______________________________________________ > >> Pw_forum mailing list > >> Pw_forum at pwscf.org > >> http://www.democritos.it/mailman/listinfo/pw_forum > > > > > > > > _______________________________________________ > > Pw_forum mailing list > > Pw_forum at pwscf.org > > http://www.democritos.it/mailman/listinfo/pw_forum > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum
