Ab initio Molecular and Solid-state Studies of the Spin Crossover System [Fe(phen)2(NCS)2]

Ab initio computations are reported for both the isolated molecule and the extended solid within the density functional theory to assess the electronic structure and derived physical properties of [Fe(phen)(2)(NCS)(2)] in which Fe-II is characterized by either one of two spin states, i.e. high spin (HS, t2(g)(4)e(g)(2)) and low spin (LS, t2(g)(6)e(g)(0)). For molecular HS and LS configurations, the characteristic IR and Raman spectra have been computed with vibrational frequencies magnitudes and their assignments in relative agreement with the experiment. For the extended solid, the equilibrium total energies reproduce the correct LS ground state. From the calculated equations of state for the two forms, a pressure-induced HS -> LS transition is proposed.