Mr. Sharma,

You can use Gamess-US (http://www.msg.ameslab.gov/gamess/).

Ms. Bojidarka B. Ivanova,

could you please explain how we can use GAMESS to calculate delta G?

Gibbs free energy (G = E + PV − TS) per atom at 0 K, G is equivalent to the enthalpy (G = H = E + PV).

VASP calculate the total energy at 0 K.

https://www.researchgate.net/post/How_does_calculate_the_Gibbs_free_energy_from_DFT_using_VASP2

Hi Dr. Alberto Rubio Ponce

Is it possible for the VASP to calculate energy at T!=0 ?

Check the ground state definition.

You would need to calculate phonon values (i.e., frequencies). You can do that by the phonopy software.

You can try VaspGibbs (https://github.com/ftherrien/VaspGibbs) it was made to do exactly this.

In this case, to get adsorption energy, assuming you have already computed total energies with VASP you would do:

$ cd slab+adsorbate_folder

$ vasp_gibbs -o 1 2 -T 300

$ cd ../adsorbate_folder

$ vasp_gibbs --molecule -T 300

Assuming for example that your adsorbate is a diatomic molecule and that its atoms are the first two atoms in the POSCAR of the slab+adsorbate system. Gibbs free energies would be found in slab+adsorbate_folder/VaspGibbs.md and adsorbate_folder/VaspGibbs.md. The difference between the two would give you adsorption free energy.

Note: VaspGibbs would automatically rerun VASP for you to obtain frequencies (which is necessary, as mentioned in Mohammednoor Altarawneh's answer)