Helium dimer potential from symmetry-adapted perturbation theory calculations using large Gaussian geminal and orbital basis sets

The symmetry-adapted perturbation theory (SAPT) has been employed to calculate an accurate potential energy curve for the helium dimer. For major components of the interaction energy, saturated values have been obtained using extended Gaussian-type geminal bases. Some other, less significant components were computed using a large orbital basis and the standard set of SAPT codes. The remaining small fraction of the interaction energy has been obtained using a nonstandard SAPT program specific for two-electron monomers and the supermolecular full configuration interaction (FCI) calculations in a moderately large orbital basis. Accuracy of the interaction energy components has been carefully examined. The most accurate to date values of the electrostatic, exchange, induction, and dispersion energies are reported for distances from 3.0 to 7.0 bohr. After adding the retardation correction predicted by the Casimir theory, our new potential has been shown [A. R. Janzen and R. A. Aziz (submitted)] to recover the known bulk and scattering data for helium more accurately than other existing ab initio and empirical potentials. However, the calculated dissociation energy of 1.713 mK and the bond length of 45.8 Angstrom differ somewhat from the values inferred recently from a transmission experiment using nanoscale sieves. (C) 1997 American Institute of Physics.