Constrained nuclear-electronic orbital second-order Moller-Plesset perturbation theory

TL;DR

The paper introduces a new multicomponent MP2 method within the CNEO framework that efficiently captures nuclear quantum effects on molecular properties, reducing computational costs.

Contribution

It develops and benchmarks a constrained nuclear-electronic orbital MP2 method that includes electronic-nuclear correlation for vibrationally averaged properties.

Findings

Accurately predicts internuclear distances and vibrational frequencies.

Captures nuclear vibrational effects without additional force constant calculations.

Demonstrates effectiveness on diatomic and small polyatomic molecules.

Abstract

A multicomponent second-order M{\o}ller-Plesset perturbation theory (MP2) method is derived and implemented within the constrained nuclear-electronic orbital (CNEO) framework from a multicomponent generalization of the Hylleraas functional. The CNEO-MP2 method includes electronic-nuclear and nuclear correlation in the calculation of vibrationally averaged molecular properties. Nuclear quantum effects like vibrational averaging, isotopic effects, and zero-point energy can be captured in a single calculation or geometry optimization with CNEO-MP2, eliminating the need to perform costly subsequent calculations to determine higher order force constants as required with many existing methods used to determine vibrational effects upon molecular properties. The CNEO-MP2 method is benchmarked on a test set of diatomic and small polyatomic molecules and ions. Herein, we present internuclear distances, bond angles, potential energy surfaces, and vibrational frequencies calculated with the CNEO-MP2 method to demonstrate that it correctly captures the effects of nuclear vibrational motion upon molecular properties.