Basis Set Convergence of Potential Energy Surfaces: Ground Electronic State of H2 and H3+

The convergence behavior of the total energy with the increase of the basis set is analyzed in two-electron systems, H-2 and H-3(+), where the source of error is the basis set truncation. Extrapolation of total energy to the complete basis set limit is carried out with the exponential and inverse cubic power (or higher order) functional forms, as a function of the cardinal number X that describes the correlation consistent basis sets, used in this work. The ability of the different extrapolation schemes to generate accurate potential energy curves or surfaces, over a wide range of geometries, is examined, following the criteria outlined by Halkier et al. (Chem Phys Lett, 1999, 310, 385). Comparison with the most accurate potential energy curve and surface for the ground electronic state of H-2(X-1 Sigma(+)(g)) and H-3(+) (1A'), respectively, shows that a simple two point extrapolation with the quintuple and sextuple zeta correlation-consistent basis sets results yields to practically "spectroscopic accuracy." To assess the precision of the extrapolated potential energy surfaces, several properties are compared with the most accurate ones. As an example, the vibrational energies obtained with the extrapolated energies have an error of only a few tenths of a cm(-1). (c) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 387-399, 2011