Multireference configuration interaction potential curve and analytical potential energy function of the ground and low-lying excited states of CdSe

The potential energy curves (PECs) of the ground state ($^{3}Pi )$and three low-lying excited states ($^{1}Sigma $, $^{3}Sigma $,$^{1}Pi )$ of CdSe dimer have been studied by employingquasirelativistic effective core potentials on the basis of thecomplete active space self-consistent field method followed bymultireference configuration interaction calculation. The four PECsare fitted to analytical potential energy functions using theMurrel--Sorbie potential function. Based on the PECs, the vibrationallevels of the four states are determined by solving theSchr"{o}dinger equation of nuclear motion, and correspondingspectroscopic constants are accurately calculated. The equilibriumpositions as well as the spectroscopic constants and the vibrationallevels are reported. By our analysis, the $^{3}Pi $ state, of whichthe dissociation asymptote is Cd($^{1}$S) + Se($^{3}$P), isidentified as a ground state of CdSe dimer, and the correspondingdissociation energy is estimated to be 0.39,eV. However, the firstexcited state is only 1132.49,cm$^{ - 1}$ above the ground state andthe $^{3}Sigma $ state is the highest in the four calculated states.