Combined DFT and NBO approach to analyze reactivity and stability of (CuS)n (n=1-12) clusters

Copper sulfide nanoparticles are attracting attention due to their interesting plasmonic properties, with potential applications in medicine and photocatalysis. In this work, copper sulfide clusters (CuS)(n), n = 112, are theoretically studied through DFT and Natural Bond Orbital (NBO) analysis. Initial random structures were optimized using the DFT method to obtain ground state structures. CuS clusters adopt 3-D geometries from n = 4. Layered (n = 6, 8) and hollow (n = 4, 5, 7, 9, 10, 12) structures appear in this study, the latter with copper atoms forming hollow frameworks. Reactivity descriptors are calculated and electrophilicity index is correlated to electron affinity. Charge transfer occurs in general from copper to sulfur atoms, as shown by NBO analysis. For the closed-shell (CuS)6,8,10 clusters, stabilization energy shows that the dominant orbital interactions correspond to donor-acceptor orbitals sigma(cu-s) -> n*(cu), sigma(cu-s) -> sigma*(cu-sn), n(s) sigma*(s-s), respectively. Electrostatic potential maps reveal regions of large and low electron density surrounding S and Cu atoms, respectively. (C) 2017 Elsevier B.V. All rights reserved.