Theoretical study on the ground and excited states of MnO₄ ^-

The symmetry adapted cluster (SAC) and SAC-configuration interaction (SAC-CI) theories are applied to the calculations of the ground and excited states of MnO₄^-. With the use of three different active spaces, we examine the convergence of the results. Electron correlations work to relax charge polarizations of the Mn-O bonds in the ground state. The experimental spectrum of MnO₄^- is well reproduced by the present calculations. All of the observed peaks are assigned to the electronic allowed transitions to the ¹T₂ excited states. They are characterized as the excitations from the nonbonding Orbitals of oxygen to the antibonding orbitals between the metal and oxygens. For reasonable descriptions of the ground and excited states of MnO₄^-, electron correlations should be considered with the use of large enough active space for expressing the relaxations of valence electrons. In this sense, all of the previous theoretical assignments of the spectra are unreliable, since they are not the results of calculations including sufficient amount of electron correlations.