Potential energy surface of the 2A' Li2+Li doublet ground state

TL;DR

This paper computes the potential energy surface of the lithium trimer's ground state using advanced quantum chemistry methods, emphasizing core-valence correlation and interpolation techniques for accurate molecular property predictions.

Contribution

It introduces a detailed ab initio calculation of the 2A' state of Li3, incorporating core-valence correlation and interpolation methods, and investigates Jahn-Teller effects with multiple electronic structure theories.

Findings

Accurate bond lengths, frequencies, and dissociation energies require core-valence correlation.

Interpolation with moving least squares effectively models the potential energy surface.

Jahn-Teller splitting into 2A1 and 2B2 states is characterized using CASSCF and FCI methods.

Abstract

The lowest doublet electronic state for the lithium trimer (2A') is calculated for use in three-body scattering calculations using the valence electron FCI method with atomic cores represented using an effective core potential. It is shown that an accurate description of core-valence correlation is necessary for accurate calculations of molecular bond lengths, frequencies and dissociation energies. Interpolation between 2A' ab initio surface data points in a sparse grid is done using the global interpolant moving least squares method with a smooth radial data cutoff function included in the fitting weights and bivariate polynomials as a basis set. The Jahn-Teller splitting of the 2E' surface into the 2A1 and 2B2 states is investigated using a combination of both CASSCF and FCI levels of theory. Additionally, preliminary calculations of the 2A'' surface are also presented using second order spin restricted open-shell Moller-Plesset perturbation theory.