[Pw_forum] Calculation of Gibbs free energies

[Torstein Fjermestad]

 Dear GAO Zhe,

 Thanks for your suggestion. Of cause one can calculate the vibrational 
 free energy directly from the frequencies. I did not think about that. 
 :(

 Regards

 Torstein Fjermestad
 University of Oslo
 Norway


 On Wed, 11 Jul 2012 17:54:42 +0800 (CST), "GAO Zhe" 
 <flux_ray12 at 163.com> wrote:
> According to my experience, the general process is right, but, this
> general process is normally working for crystal rather than 
> amorphous,
> liquid and gas. Since the contribution from vibration is not that 
> much
> in those matter, for example, transition contributes much more in gas
> phase. Therefore, Monte Carlo or Molecular Dynamic could be better
> choice in these cases.
> Technically, in your calculation, H2O molecule may exist in a box,
> therefore only the Gamma phonon calculation is meaningful. Since q2r
> means fitting the finite samplings of dynamic matrics to infinite
> interatomic force constants, only one point is not that reliable to
> find good aproach of IFCs. Actually, since vibrational free energy is
> defined with the term of hv, you can derectly obtain Fvib from your
> first step.
>
> --
> GAO Zhe
> CMC Lab, Materials Science & Engineering Department,
> Seoul National University, South Korea
>