The optimized geometries were determined by Equilibrium Geometry (EG) calculations. In present work, energy differences contain corrections of zero-point energy (ZPE) computed by use of frequency (vibrational) calculations via Single Point Energy (SPE) calculations. Additionally, the adsorption enthalpy and Gibbs free energy values and vibrational frequencies were obtained by frequency calculations at a temperature of 298 K because no experimental thermochemistry data are available for H2S adsorption on M–ZSM-12 zeolites (where M = Fe, Co, Ni, Cu and Zn atoms). A factor of 0.9613 [58] was used to scale all frequency values to reproduce experimental fundamentals. Mulliken atomic charges of atoms have been obtained by Mulliken population analysis [59]. HOMO and LUMO energy values and orbital representations have been computed by full population analysis. Chemical hardness, chemical potential and electronegativity were used to compare the activity ofmetal exchanged ZSM-12 clusters. These valueswere calculated using below equations which can be expressed in terms of the highest occupied molecular orbital energy (ЄHOMO) and the lowest unoccupied molecular orbital energy (ЄLUMO) by using approximation of Koopmans [60–63].