Issue 29, 2023

An approximation to the vibrational coupled-cluster method for CH-stretching of large molecules: application to naphthalene and anthracene

Abstract

We propose an approximation to the vibrational coupled-cluster method (VCCM) to describe the CH-stretching region of the vibrational spectrum of large molecules. The vibrational modes of a molecule are divided into two sets: the target set and the bath set. The target set includes the CH stretches and the modes that are strongly coupled with the CH stretches and/or involve strong Fermi resonances with a CH stretch fundamental. The rest of the modes are in the bath set. First, the effective harmonic oscillator (EHO) approximation is invoked for the whole system to obtain the zeroth-order frequencies and modified potentials. The effects of interaction between the bath set and the target sets are included in the modified potential from the EHO calculation. The VCCM equations are constructed with the modified potential from the EHO calculations and for the target set only. The transition energies and intensities are calculated using such a truncated VCCM approximation. The proposed method is applied to calculate the IR spectra of naphthalene and anthracene. The results with three different criteria for selecting the modes in the target set are compared with the experimental IR spectra.

Graphical abstract: An approximation to the vibrational coupled-cluster method for CH-stretching of large molecules: application to naphthalene and anthracene

Supplementary files

Article information

Article type
Paper
Submitted
23 Mar 2023
Accepted
27 Jun 2023
First published
30 Jun 2023

Phys. Chem. Chem. Phys., 2023,25, 20076-20092

An approximation to the vibrational coupled-cluster method for CH-stretching of large molecules: application to naphthalene and anthracene

N. Palanisamy and S. Banik, Phys. Chem. Chem. Phys., 2023, 25, 20076 DOI: 10.1039/D3CP01313H

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