SYMMETRY-ADAPTED PERTURBATION-THEORY OF 3-BODY NONADDITIVITY IN AR TRIMER

The symmetry-adapted perturbation theory has been used to compute the three-body nonadditivity of Ar-3 interaction. Several components which had not been considered before have been taken into account. A comple te nonadditive potential surface has been fitted to 36 computed points . It is found that all of the dispersion components considered, includ ing the famous Axilrod-Teller-Muto term, are significantly damped at s hort to intermediate interatomic separations. Functional forms describ ing this damping are obtained from fits to computed values. It is also seen that the leading intramonomer correlation correction to the disp ersion energy cannot be ignored as it typically provides about 15% con tribution to this energy. The fourth-order dispersion energy is simila rly important at intermediate distances. Both components have not been considered before and appear to be necessary for accurate description of Ar-3 interaction. The nonadditivity of the more complicated exchan ge energies has been examined through second-order including an analys is of the expansion in powers of the interatomic overlap integrals. (C ) 1997 American Institute of Physics.