Comparative analysis of geometry, relative stabilities, optoelectronic and thermochemical properties of [CuX+2]λ and [CuX-Ag-Au]λ nanoalloy clusters (λ = 0, ± 1; X = 1 − 13): a DFT approach

A comparative study of geometry, relative stabilities, optoelectronic and thermochemical properties of [Cu_X-Ag-Au]^λ and [Cu_X+2]^λ (λ = 0, ± 1; X = 1 - 13) nanoalloy clusters is performed by using density functional theory (DFT) technique. The ground state configuration as well as low lying isomers of these clusters are analyzed. Binding energies, fragmentation energies and second-order difference in energies of these clusters show an odd-even alteration behavior with the size of the cluster. Result exhibits that incorporation of Ag and Au atoms in [Cu_X+2] enhances the energy gap of overall system in most of the cases. Highest Occupied Molecular Orbital (HOMO) - Lowest Unoccupied Molecular Orbital (LUMO) energy gap of [Cu_X+2] and [Cu_X-Ag-Au] are found between 0.870 and 3.490 eV and 1.237-3.196 eV respectively. The result shows that HOMO-LUMO energy gap of [Cu_X-Ag-Au] clusters are in the optimum range needed for photovoltaic devices, it signifies that these clusters may be considered as potential candidate for optoelectronic and photovoltaic devices. Data reveals that [Cu_X-Ag-Au] at X = 4 show maximum value of HOMO-LUMO gap, Vertical Ionization Energy (VIE), and hardness whereas minimum value of softness. However, at X = 13 it has demonstrated minimum value of HOMO-LUMO gap, and hardness whereas maximum value of softness and electrophilicity index. It is observed that [Cu₁₄] and [Cu₁₁-Ag-Au] clusters have significant electron infusion abilities due to large Vertical Electron Affinity (VEA) value. Optical properties - optical electronegativity, refractive index, dielectric constant as well as infrared and Raman spectra of these clusters are analyzed. For [Cu_X+2], minimum and maximum refractive index is found in case of [Cu₁₀] and [Cu₁₄] respectively, whereas for trimetallic clusters, [Cu₁₃-Ag-Au] and [Cu₄-Ag-Au] show the maximum and minimum refractive index. Thermochemical properties like thermal energy, heat capacity, zero-point correction and entropy of these systems increase with the cluster size, whereas Gibbs free energy follows reverse pattern.