LAUSR

Abstract In Hartree-Fock calculations for atoms and molecules, multicenter-expansion methods are commonly used, especially those based on linear combinations of atomic orbitals (LCAO) using Gaussian-type orbitals (GTOs) or Slater-type orbitals (STOs). Artificial nodes, which are not expected to exist in real wave functions, arise in many calculations. For the hydrogen molecular ion (H2+) there are no nodes in the exact solution of its ground state ((1σg) 2Σg). The occurrence of artificial nodes and the cause of the problem are investigated for this state. Calculations of LCAO with GTOs and of single-center expansion (SCE) with Laguerre-type orbitals (LTOs) have been performed as part of this study. It is found that an excess of diffuse basis functions is responsible for artificial nodes.