Density functional theory was utilized to investigate the molecular adsorption behavior of the hydrogen on small neutral Cu_nAg_m bimetallic nanoclusters for n+m ≤ 8. The geometries, stabilities, electronics, frequencies, and magnetic properties of both Cu_nAg_m and Cu_nAg_mH₂ clusters have been investigated by using Gaussian 16 software package. LanL2DZ basis set was used on both silver and copper atoms while aug-cc-pVQZ basis set used for hydrogen atom along with the B3LYP functional. The optimized structures of Cu_nAg_m clusters show that copper atoms always tend to occupy at the middle position at where an atom can have optimum number of coordination and hydrogen molecule favors to interact with the copper atom in mixed Cu_nAg_m clusters. Average binding energies of copper clusters higher than those of silver clusters in same size indicating the higher stability of copper systems over the silver systems and ABE is higher for hydrogen adsorbed clusters than the bare clusters which suggests hydrogen adsorption enhance the thermodynamic stability of Cu_nAg_m clusters. The adsorption of H₂ molecule noticeably favors the sites at where most positively charged environment persists. The calculated HLGs, AIPs, AEAs, VIPs, VEAs and chemical hardness of both Cu_nAg_m and Cu_nAg_mH₂clusters show obvious odd-even oscillation behavior indicating that even-numbered clusters possess higher chemical stability than odd-numbered clusters. Charge transfer analysis and frontier molecular orbital analysis further reveals that some of the heterogeneous clusters of six atoms and above have hydrogen adsorption energy within the range of -6 to -18 kJ mol^-1, which could be potential candidates for hydrogen storage materials.

Gammanage Sathya Perera

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