Vibrational properties of nanographene

TL;DR

This study investigates the vibrational properties of nanographene clusters using atomistic simulations, analyzing eigenmodes, density of states, and thermodynamic properties to understand their mechanical and thermal behavior.

Contribution

It introduces a detailed computational approach to analyze vibrational modes and thermodynamic properties of nanographene clusters, including effects of edge defects and passivation.

Findings

High-frequency shear modes in symmetric and defective clusters.

Specific heat converges to bulk graphene values with increasing cluster size.

Vibrational density of states reflects cluster symmetry and defects.

Abstract

The eigenmodes and the vibrational density of states of the ground state configuration of graphene clusters are calculated using atomistic simulations. The modified Brenner potential is used to describe the carbon-carbon interaction and carbon-hydrogen interaction in case of H-passivated edges. For a given configuration of the C-atoms the eigenvectors and eigenfrequencies of the normal modes are obtained after diagonalisation of the dynamical matrix whose elements are the second derivative of the potential energy. The compressional and shear properties are obtained from the divergence and rotation of the velocity field. For symmetric and defective clusters with pentagon arrangement on the edge, the highest frequency modes are shear modes. The specific heat of the clusters is also calculated within the harmonic approximation and the convergence to the result for bulk graphene is investigated.