Gibbs Free Energy Calc

[markmick]

Can ATK determine Gibbs energy?  If so, how is it done and where does the value show up the Lab Floor?  I couldn't find any info in the tutorials, other than a mention that ATK can compute Gibbs.

Sincerely,
Mark

[Jess Wellendorff]

Dear Mark.

ATK does not have built-in functionality for directly computing the Gibbs free energy. ATK should, however, provide all the components needed (total energy, vibrational modes/phonons, etc). But we can currently not provide you a script with a bullet-proof recipe for calculating the Gibbs energy for either gas-phase or solid-state substances. But it should in principle be possible with some manual scripting effort.

[Julian Schneider]

The free energy of (approximately) harmonic solids can be calculated using a calculation similar as in the attached script.

Formally, for the Gibbs free energy a volume term pV can be added (where p is the external pressure, and V is the system volume), which might make sense if you want to compare the free energies at different volumes  (although the pV correction is typically tiny).
Depending on what properties you are interested in, you could also include  the electronic contributions to the free energy.
If the system has pronounced anharmonic contributions or is not even in the solid state (e.g gas phase molecules or liquids), it of course more complicated to obtain the absolute Gibbs free energy.