Negative normal restitution coefficient for nanocluster collisions

TL;DR

This paper investigates nanocluster collisions, revealing that traditional restitution coefficients can be negative and proposing a new positive definition, supported by molecular dynamics simulations and continuum theory.

Contribution

It introduces a revised definition of the restitution coefficient for nanoclusters and demonstrates the applicability of macroscopic concepts at the nanoscale.

Findings

Standard restitution coefficient can be negative for nanoclusters.

A new positive definition of restitution coefficient is proposed.

Continuum theory aligns well with molecular dynamics results.

Abstract

The oblique impacts of nanoclusters is studied by means of Molecular Dynamics and theoretically. In simulations we explore two models -- Lennard-Jones clusters and particles with covalently bonded atoms. In contrast to the case of macroscopic bodies, the standard definition of the normal restitution coefficient yields for this coefficient negative values for oblique collisions of nanoclusters. We explain this effect and propose a proper definition of the restitution coefficient which is always positive. We develop a theory of an oblique impact based on continuum model of particles. A surprisingly good agreement between the macroscopic theory and simulations leads to the conclusion, that macroscopic concepts of elasticity, bulk viscosity and surface tension remain valid for nanoparticles of a few hundreds atoms.