no because it is not valid for negative frequncy in phonon spectrum
2011/10/9 GAO Zhe <flux_ray12 at 163.com> > Dear QE developer and users: > I am using QE 4.3.2 to calculate phonon and thermaldynamis properties of > materials. These days, I need to find the Gibbs (or Helmholtz) Free energy > of carbon. Thus, I compared diamond and graphite phases at 0K. As a result, > graphite provides lower energy per carbon atom (about 0.3eV/atom lower than > of diamond). > However, the phonon dispersion result shows that the imaginary frequency > occurred at Gamma, H, A and K, so it is impossible by using QHA to find the > vibrational free energy at specified temperature. > The graphite model I used is: > *ibrav = 0 , > celldm(1) = 1.889725989 , > CELL_PARAMETERS > 2.130421558318710 -1.229999460182690 0.000000000000000 > 0.000000000000000 2.459998920365380 0.000000000000000 > 0.000000000000000 0.000000000000000 6.800000000000000 > ATOMIC_POSITIONS crystal > C 0.0000000000000000 0.0000000000000000 0.2500000000000000 > C 0.0000000000000000 0.0000000000000000 0.7500000000000000 > C 0.3333333333333330 0.6666666666666669 0.2500000000000000 > C -0.3333333333333330 -0.6666666666666669 0.7500000000000000* > Is there any other methods or models can calculate the free energy of > graphite at specified temperature? > Any suggestion will be welcome. > Thanks. > > -- > GAO Zhe > CMC Lab, MSE, SNU, Seoul, S.Korea > > > > _______________________________________________ > 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/20111009/40c5d362/attachment.htm
