Pseudonatural Orbitals as a Basis for the Superposition of Configurations. II. Energy Surface for Linear H3

Abstract

A superposition of configurations (SOC) trial function is applied to the calculation of the H₃ energy surface. The convergence of the SOC trial function is improved by constructing the configurations with approximate or pseudonatural orbitals (PNO). For a given atomic‐function basis the PNO exhaust the accuracy of that basis in relatively few configurations compared to the total of all possible configurations. Gaussian‐type functions (GTF) are then practicable as a basis for a SOC trial function. Results are presented for the linear H₃ energy surface. The error when one hydrogen is removed to infinity is 0.1 eV, and an extrapolation of this error yields a “probable” barrier energy of 0.53 eV or 12 kcal.