The Ground State Potential for the Chromium Dimer Revisited

Results are presented from a new theoretical study of the ground state potential curve of the chromium dimer using multiconfiguration second-order perturbation theory. A new basis set of the atomic natural orbital type is used where the construction includes correlation of the semi-core 3p orbitals and scalar relativistic effects are added using the Douglas-Kroll Hamiltonian. The active space used in the CASSCF/CASPT2 calculations comprised 16 orbitals with 12 active electrons. The resulting ground state potential is in agreement with experiment. Computed spectroscopic constants are (with experimental values within parentheses): R e = 1.66 (1.68) Å, D 0 = 1.65 (1.53 ± 0.06) eV, ∆ G 1/2 = 413 (452) cm -1 . Higher vibrational frequencies are also well reproduced.