Size-dependent melting: Numerical calculations of the phonon spectrum

TL;DR

This study investigates how the phonon spectra of nanoparticles change with size and how this affects their melting temperatures, using a simplified lattice model to reveal fundamental size-dependent vibrational behaviors.

Contribution

It introduces a minimal harmonic lattice model to analyze size-dependent phonon spectra and their influence on nanoparticle melting temperatures.

Findings

Density of low energy phonon modes increases as nanoparticle size decreases.

Size-dependent phonon behavior explains surface-premelting phenomena.

The model captures essential physics of nanoparticle melting processes.

Abstract

In order to clarify the relationship between the phonon spectra of nanoparticles and their melting temperature, we studied in detail the size-dependent low energy vibration modes. A minimum model with atoms on a lattice and harmonic potentials for neighboring atoms is used to reveal a general behavior. By calculating the phonon spectra for a series of nanoparticles of two lattice types in different sizes, we found that density of low energy modes increases as the size of nanoparticles decreases, and this density increasing causes decreasing of melting temperature. Size-dependent behavior of the phonon spectra accounts for typical properties of surface-premelting and irregular melting temperature on fine scales. These results show that our minimum model captures main physics of nanoparticles. Therefore, more physical characteristics for nanoparticles of certain types can be given by phonons and microscopic potential models.