Quantum and classical vibrational relaxation dynamics of N-methylacetamide on ab initio potential energy surfaces

TL;DR

This paper investigates vibrational relaxation in N-methylacetamide using ab initio calculations, comparing quantum and classical methods to evaluate their accuracy and applicability for biomolecular energy transfer studies.

Contribution

It provides a detailed quantum-chemical analysis of vibrational relaxation pathways and assesses classical and perturbative approaches against exact quantum results.

Findings

Quantum calculations reveal sensitive energy transfer pathways.

Classical and perturbative methods have varying degrees of accuracy.

Strategies for modeling vibrational relaxation in biomolecules are proposed.

Abstract

Employing extensive quantum-chemical calculations at the DFT/B3LYP and MP2 level, a quartic force field of isolated N-methylacetamide is constructed. Taking into account 24 vibrational degrees of freedom, the model is employed to perform numerically exact vibrational configuration interaction calculations of the vibrational energy relaxation of the amide I mode. It is found that the energy transfer pathways may sensitively depend on details of the theoretical description. Moreover, the exact reference calculations were used to study the applicability and accuracy of (i) the quasiclassical trajectory method, (ii) time-dependent second-order perturbation theory, and (iii) the instantaneous normal mode description of frequency fluctuations. Based on the results, several strategies to describe vibrational energy relaxation in biomolecular systems are discussed.