Phonon density of states of magnetite (Fe3O4) nanoparticles via molecular dynamics simulations

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 simulations 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 vibrational 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. Our results close a gap by providing a systematic phonon density of states study on magnetite nanoparticles and outline a reusable framework for characterizing similar nanomaterials. • The PDOS in Fe 3 O 4 nanoparticles was studied using molecular dynamics simulations. • Classical force fields are comparable with X-ray, INS, and DFT results. • The particle size significantly affects the PDOS, showing distinctive surface modes. • The phonon density of states weakly depends on temperature between 100 K and 400 K. • Surface H 2 O molecules affect the DOS and strongly depend on temperature.