where, ∆ZPE is the difference in zero-point energies, ∆S is the change in entropy due to vibrational contributions, and ∆GU = -eU, where U is the applied electrode potential. The values of (∆ZPE-T∆S) for the reference molecule (H2 gas) is 0.1328 eV. Calculated values of adsorption energies, (∆ZPE-T∆S), free energies of hydrogen adsorption are given in Table .