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First principles study of electronic structure for cubane-like and ring-shaped structures of M4O4, M4S4 clusters (M = Mn, Fe, Co, Ni, Cu)

Spin-polarized DFT has been used to perform a comprehensive study of the geometric structures and electronic properties for isolated M4X4 nano-clusters between their two stable isomers - a planar rhombus-like 2D structure and a cubane-like 3D structure with M = Mn, Fe, Co, Ni, Cu ; X = O, S. These two structural patterns of the M4X4 clusters are commonly found as building blocks in several poly-nuclear transition metal complexes in inorganic chemistry. The effect of the van der Waals corrections to the physical properties have been considered in the electronic structure calculations employing the empirical Grimme's correction (DFT+D2). We report here an interesting trend in their relative structural stability - the isolated M4O4 clusters prefer to stabilize more in the planar structure, while the cubane-like 3D structure is more favourable for most of the isolated M4S4 clusters than their planar 2D counterparts. Our study reveals that this contrasting trend in the relative structural stability is expected to be driven by an interesting interplay between the s-d and p-d hybridization effects of the constituents' valence electrons.