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 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20111009/62e49347/attachment.htm
