AN AB-INITIO STUDY OF THE INTERMOLECULAR POTENTIAL SURFACES OF HE-CH4AND NE-CH4

The intermolecular potential surfaces for the Van der Waals complexes He-CH4 and Ne-CH4 are studied by ab initio theory using complete fourt h-order Moller-Plesset perturbation theory (MP4) with an efficient bas is set containing bond functions. For He-CH4, the global minimum occur s at R = 3.4 Angstrom, theta = 180 degrees, phi = 180 degrees (in a Ja cobi coordinate system) with a minimum energy D-e = -26.2 cm(-1). For Ne-CH4, the global minimum occurs at R = 3.5 Angstrom, theta = 180 deg rees, phi = 0 degrees with a minimum energy D-e = -59.0 cm(-1). Two sa ddle points were found for each of the systems. The potential energy s urfaces are compared with the semiempirical surfaces and recent ab ini tio results on the same systems. (C) 1997 Elsevier Science B.V.