Intermolecular potential energy surfaces of weakly bound dimers computed from ab initio density functional theory: The right answer for the right reason

Ab initio density functional theory has been applied for the weakly interacting, He2, He-Be2+, Ne2 and Be2. The results are competitive with the highly accurate coupled-cluster method. The original implementation of the method, which includes correlation, [I. Grabowski, S. Hirata, S. Ivanov, R.J. Bartlett, J. Chem. Phys. 116 (2002) 4415] significantly overestimates the binding in all cases. However, using semi-canonical orbitals as in generalized many-body perturbation theory leads to consistently good potential energy surfaces. The notorious Be dimer potential is about 30% too deep, but virtually parallel to reference results, and much better than MP2.