Pd2: A dimer with two Kohn-Sham triplet ground states

Abstract
We calculate the dissociation energy, equilibrium bond length, and vibrational frequency of Pd2 using local-spin-density theory and the fully relativistic norm-conserving pseudopotential. Over a range of bond lengths which includes the equilibrium length, we find a nonmagnetic and an antiferromagnetic singlet, as well as two triplet Kohn-Sham, ground states. The dissociation energy for the absolute ground state (a triplet) is 1.61 eV, which is in only fair agreement with the experimental value of 1.09 eV.