Transition metal dichalcogenides (TMDs) (MX 2 ; M =W, Mo; X = S, Se, Te) encompass a large href="https://en.wikipedia.org/wiki/Graphite" graphite , TMDC bulk crystals are formed of monolayers bound to each other by Van-der-Waals attraction . In each monolayer, atoms sticks together with Covalent bonds .additionally a transition from indirect bandgap (1.1eV) in the bulk limit to direct bandgap(1.5eV) in the quantum (2D) limit exists. ince the discovery of graphene , two-dimensional Nano structures have attracted lots of interests in Nano-science and condensed matter physics. In Nano size TMDC is very useful for hydrogen evolution reaction (HER) catalyst. So far no Comprehensive research on MoSe2 Nano materials has appear in literally. Nano structure or nanocluster are often quite different from bulk and could have interesting properties but these are yet to be well understood. Here we present search structure results on stoichiometric (MoSe 2 ) n n=1-10 clusters and report the electronic and optical properties. For search structure we employ USPEX code which is based on evolutionary algorithm. This code unable to relax structures and can just produce them. For relaxation we use of full-potential density functional theory (DFT approach) by FHI-aims code within four different exchange-correlation functional. The electronic properties and energy gap of the lowest energy isomers were computed within several schemes, including semi local PBE and BLYP functional, hybrid B3LYP ,PBE0 functional, many body based DFT+GW approach, and fundamental gap calculations. Vibrational spectra of the lowest lying isomers, computed by the force constant method, are used to address IR spectra of the clusters. At the end we investigate the temperature effect by using Helmholtz free energy definition.
