Phonon density of states of magnetite (\ce{Fe3O4}) nanoparticles via molecular dynamics simulations

TL;DR

This paper uses molecular dynamics simulations to study how nanoparticle size, water adsorption, and temperature affect the phonon density of states in magnetite nanoparticles, revealing size-dependent broadening and softening of phonon modes.

Contribution

It provides a detailed computational analysis of magnetite nanoparticle phonon properties, highlighting the effects of size, water, and temperature, and compares force fields against experimental data.

Findings

Decreased nanoparticle size causes phonon broadening and softening.

Water adsorption extends the phonon spectrum to higher energies.

Temperature increases lead to slight phonon broadening and softening.

Abstract

This study presents a comprehensive computational investigation of magnetite nanoparticles, systematically evaluating a range of force fields against experimental results. We analyze the influence of particle size, temperature, and surface-adsorbed water molecules on the structural and dynamic properties of the nanoparticles. We performed classical molecular dynamics of nanoparticles and bulk magnetite and utilized density functional theory calculations for bulk magnetite for comparison. Our results reveal that nanoparticle size and the presence of adsorbed water molecules have a pronounced impact on the density of states. Specifically, as the nanoparticle size is decreased, phonon modes exhibit significant broadening and softening, which is attributable to reduced phonon lifetimes resulting from enhanced boundary scattering. The incorporation of water further broadens the density of states and extends the spectra to higher energy regions. Temperature variations result in a slight broadening and softening of the phonon density of states, particularly in the oxygen-dominated region, which is attributed to phonon anharmonicity.