Vibrational Levels of a Generalized Morse Potential

TL;DR

This paper introduces numerical methods to accurately compute vibrational levels of a generalized Morse potential, improving efficiency and precision over existing techniques for diatomic molecules.

Contribution

It develops and applies several Galerkin-based numerical approaches to solve the GMP vibrational problem, demonstrating superior convergence and accuracy compared to traditional methods.

Findings

LPM achieves spectroscopic accuracy within 1-2 orders of magnitude faster.

Fewer basis functions are needed compared to CM-DVR.

Methods successfully applied to B₂, O₂, and F₂ molecules.

Abstract

A Generalized Morse Potential (GMP) is an extension of the Morse Potential (MP) with an additional exponential term and an additional parameter that compensate for MP's erroneous behavior in the long range part of the interaction potential. Because of the additional term and parameter, the vibrational levels of the GMP cannot be solved analytically, unlike the case for the MP. We present several numerical approaches for solving the vibrational problem of the GMP based on Galerkin methods, namely the Laguerre Polynomial Method (LPM), the Symmetrized Laguerre Polynomial Method (SLPM) and the Polynomial Expansion method (PEM) and apply them to the vibrational levels of the homonuclear diatomic molecules B$_2$, O$_2$ and F$_2$, for which high level theoretical Full CI potential energy surfaces and experimentally measured vibrational levels have been reported. Overall the LPM produces vibrational states for the GMP that are converged to within spectroscopic accuracy of 0.01 cm$^{-1}$ in between 1 and 2 orders of magnitude faster and with much fewer basis functions / grid points than the Colbert-Miller Discrete Variable Representation (CM-DVR) method for the three homonuclear diatomic molecules examined in this study.