A comparative study of two molecular mechanics models based on harmonic potentials

TL;DR

This study compares two molecular mechanics models, the stick-spiral and beam models, revealing significant differences in predicted mechanical properties of nanostructures, influenced by loading modes, geometry, and material type.

Contribution

It provides a systematic comparison of the two models based on energy equivalence, highlighting their differences and dependencies on structural and loading parameters.

Findings

Maximum difference in predictions exceeds 300% under certain conditions

The models' accuracy varies with nanoribbon width and loading mode

The stick-spiral model overestimates, while the beam model underestimates properties in narrow nanoribbons

Abstract

We show that the two molecular mechanics models, the stick-spiral and the beam models, predict considerably different mechanical properties of materials based on energy equivalence. The difference between the two models is independent of the materials since all parameters of the beam model are obtained from the harmonic potentials. We demonstrate this difference for finite width graphene nanoribbons and a single polyethylene chain comparing results of the molecular dynamics (MD) simulations with harmonic potentials and the finite element method with the beam model. We also find that the difference strongly depends on the loading modes, chirality and width of the graphene nanoribbons, and it increases with decreasing width of the nanoribbons under pure bending condition. The maximum difference of the predicted mechanical properties using the two models can exceed 300% in different loading modes. Comparing the two models with the MD results of AIREBO potential, we find that the stick-spiral model overestimates and the beam model underestimates the mechanical properties in narrow armchair graphene nanoribbons under pure bending condition.