Multibody analysis of potential energy surfaces for first- and second-row tetramers. I. The tetrahedral structures of P4 and N4

SCF calculations using a split-valence basis set were carried out for N₃, P₃, N₄, and P₄ showing that there are substantial structural differences between the clusters of these elements, nitrogen and phosphorus. An analysis of the nonadditive three- and four-body contributions to the binding energies of these systems is carried out and shown to be quite close to the values predicted from qualitative considerations by Murrell [Chem. Phys. Lett. 55 , 1 (1978)].