A Comparison of One-Particle Basis Set Completeness, Higher-Order Electron Correlation, Relativistic Effects, and Adiabatic Corrections for Spectroscopic Constants of BH, CH+, and NH

Abstract

To investigate the relative importance of various small sources of error in theoretical predictions of molecular properties, we report spectroscopic constants for the ground electronic states of BH, CH+, and NH, which are nearly converged to the adiabatic ab initio limit. Computations are performed using full configuration interaction and coupled-cluster singles, doubles, and perturbative triples methods with correlation-consistent basis sets of double- to sextuple-ζ quality. The equilibrium bond lengths, re, harmonic vibrational frequencies, ωe, anharmonicity constants, ωexe, centrifugal distortion constants, De, and other quantities are compared with experiment for each species. The systematic dependence of spectroscopic constants on the one-particle basis is used to estimate the complete basis set limit values by using a two-point linear extrapolation scheme. The importance of core correlation, scalar relativistic corrections, higher-order electron correlation, and basis set completeness are carefully...