A DFT study of structural and electronic properties of copper indium ditelluride Cu_<i>m</i>−1In_<i>m</i>Te_{2<i>m</i>−2} with <i>m</i> = 2–5 neutral and anion clusters

In this work, the electronic and structural properties of Cu _<i>m</i>-1In _<i>m</i> Te_2<i>m</i>-2 neutral and anion clusters are studied. The simulations are carried out using the QUANTUM ESPRESSO/PWSCF package, based on the density functional theory (DFT) principle, which employs a pseudo-potential with a plane wave basis set. Geometry optimization starting from several initial candidate structures was performed for each cluster size to determine the number of possible minimum-energy isomers for each size. The results show that the lowest-energy structures are cubic, ranging from cluster <i>m</i> = 2 to 5, and resemble the chalcopyrite structure. The geometry of neutral and anionic cases exhibits a structural change, including distortion and a transition from two-dimensional to one-dimensional. By considering energetics, <i>i.e.</i> HOMO-LUMO gap, binding energy, ionization potential and electron affinity, the relative stability of Cu _<i>m</i>-1In _<i>m</i> Te_2<i>m</i>-2/(Cu _<i>m</i>-1In _<i>m</i> Te_2<i>m</i>-2)^- was measured. From the most stable energy structures, CuIn₂Te₂/(CuIn₂Te₂)^- were found to have enhanced chemical stability relative to their neighbours. They are a magic-number species. The binding energy and HOMO-LUMO gap of CuIn₂Te₂/(CuIn₂Te₂)^- clusters show the most significant value, which indicates high chemical stability. The adiabatic ionization potential of the cluster decreases monotonically, showing favor for metallic character as cluster size increases. Both clusters' vertical/adiabatic detachment energies also show a slight odd-even oscillation with an increasing tendency as a function of cluster size. This indicates that the successive increase in metallic atoms results in a decrease in nonmetallic favor. We also analyse the partial charge density of the optimized geometries for both anion and neutral clusters. The numerical value indicates that these clusters, including photovoltaic solar cells and other devices, make a significant contribution to semiconductor design.