Nature of stability of Mg 4 and many-body forces

Abstract

The precise ab initio calculations of the tetramer Mg 4 were performed at the all-electron CCSD(T)/aug-cc-pVQZ level. The dissociation energy in respect to all possible dissociation channels at different levels of accuracy, from SCF till CCSD(T), but with the same large basis set, was calculated. Except the SCF method, in all approximations Mg 4 was found stable. The many-body decomposition of the interaction energy was performed. From it follows that the three-body forces are not only a single factor of stabilization, but the dominant factor of the many-body expansion. The three-body interactions favor the promotion of the 3 s-valence electrons to the 3 p orbitals with the subsequent sp-hybridization.