On the use of quadratic approximants to model diatomic potential energy curves

摘要

Quadratic approximants are shown to have an appropriate functional form for modelling the mathematical structure of the full configuration interaction energy as a function of internuclear distance. The problem of spurious singularities is discussed. Quadratic approximants with additional constraints are constructed so as to avoid spurious singularities and to have the correct dissociation limits. It is shown that these approximants are appropriate for interpolating between computed ab initio energies. The method is tested with a set of full configuration interaction energies for the hydrogen fluoride molecule. The approximants are shown to give an accurate interpolation through the region of moderate bond stretching where direct approximate ab initio computations are difficult. A procedure for parameterizing the approximants to empirical data is developed.