Small doped 3He clusters: A systematic quantum chemistry approach to fermionic nuclear wavefunctions and energies
A novel approach for calculating nuclear wavefunctions and energies of 3He clusters doped with an atomic or molecular impurity is developed. It adopts the systematic and well developed methodology of quantum chemistry employing an analogy between electrons bound by Coulomb forces to the nuclei and fermionic 3He atoms clustered around a dopant species. The differences primarily concern the different shapes of the helium-helium and helium-impurity potentials and the larger mass of the 3He atom, as compared to electronic structure problems. A new integral evaluation procedure is outlined, as well as the necessary modifications to electronic structure codes. Tests against numerically exact calculations for Imp-3He (Imp = Ne, Ar, Kr, Xe, and SF6) complexes show that a modest set of 15 basis functions provides accurate and converged results. Calculations for the lowest triplet state of the SF6(3He)2 cluster, where fermionic statistics comes into play in the orbital part of the helium nuclear wavefunction, are presented. The triplet state is bound by 22 micro-hartree with respect to dissociation into 3He + SF6-3He. The applicability of the new method to larger systems is discussed.