Virial theorem decomposition as a tool for comparing and improving potential-energy surfaces: ground-state Li3

Abstract

The virial theorem has been used to decompose existing potential-energy surfaces for the ground state of Li₃ into the electronic, kinetic and potential components, and to improve some of the physical attributes to the most accurate potential-energy surface for this system. The behaviour of these components and the total energy for a C_2v uniform-scaling cut of the various surfaces is compared. The individual contributions of both two- and three-body energy terms are also discussed. Specific results are presented for the Varandas–Morais and Thompson et al. potentail-energy functions, in addition to the recent double many-body expansion (DMBE) potential-energy surface, this being the only existing Li₃ surface for which the normalization of the kinetic field, implied by the virial theorem, is satisfied. By slightly modifying adjustable parameters of the latter surface, an improved DMBE surface has been obtained with qualitatively correct trends in the kinetic and potential energy profiles. The implications for the ideal general form of a potential-energy surface are also assessed.