[Pw_forum] Can not find minimum free energy by QHA
Prof. Giannozzi: Thank you very much for your kindly reply. I think this is my problem to understand Fvib. I have also checked Axel van de Walle's Ph.D thesis, and found that free energy should be Fvib+Fconf-TSvib-TSconf. In 0GPa pressure case, Fconf should equal to total energy. Therefore I cannot obtain the right Free Energy vs Volume curve as a result of using Fvib alone. -- GAO Zhe CMC Lab, MSE, SNU, Seoul, S.Korea At 2011-08-30 03:42:31,"Paolo Giannozzi" wrote: > >On Aug 22, 2011, at 4:36 , GAO Zhe wrote: > >> However, the free energy kept decreasing as a monotone decreasing >> function of lattice parameter > >you mean: the "vibrational free energy" alone, or "the sum of the >energy and of the vibrational free energy"? the vibrational free >energy should be a small correction to the total energy. > >P. >--- >Paolo Giannozzi, Dept of Chemistry&Physics&Environment, >Univ. Udine, via delle Scienze 208, 33100 Udine, Italy >Phone +39-0432-558216, fax +39-0432-558222 > > > > >___ >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/20110831/0419a2d7/attachment.htm
[Pw_forum] Can not find minimum free energy by QHA
On Aug 22, 2011, at 4:36 , GAO Zhe wrote: > However, the free energy kept decreasing as a monotone decreasing > function of lattice parameter you mean: the "vibrational free energy" alone, or "the sum of the energy and of the vibrational free energy"? the vibrational free energy should be a small correction to the total energy. P. --- Paolo Giannozzi, Dept of Chemistry&Physics&Environment, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
[Pw_forum] Can not find minimum free energy by QHA
Dear QE Developer and Users
I am using DFPT+QHA to predict model's properties at high temperature.
According to the paper,Ab initio lattice dynamics and phase transformations of
ZrO2, Phy Rev B 71, 064301, free energyv.s. volume figure can be plotted at
certain temperature for EOS-fitting and so on.
Having determined the equlibrium lattice parameter, 8.18 a.u. , of TiC(FCC) by
both EOS-fitting and vc-relax, I chose 20 different lattice paramters
(7.98~8.38a.u.) and calculated phonon dispersion and thermodynamic properties.
However, the free energy kept decreasing as a monotone decreasing function of
lattice parameter, even when imaginary frequency began to occur at 8.88a.u..
My DFPT calculation script shows below:
cat >TiC_${INT}.scf.in TiC_${INT}.ph.in
