All-Atom Simulation Method for Zeeman Alignment and DipolarAssembly of Magnetic Nanoparticles

AU Mahmood and YG Yingling, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 18, 3122-3135 (2022).

DOI: 10.1021/acs.jctc.1c01253

Magnetic nanoparticles (MNPs) can organize intonovel structures in solutions with excellent order and uniquegeometries. However, studies of the self-assembly of smaller MNPsare challenging due to a complicated interplay between externalmagneticfields and van der Waals, electrostatic, dipolar, steric, andhydrodynamic interactions. Here, we present a novel all-atommolecular dynamics simulation method to enable detailed studies ofthe dynamics, self-assembly, structure, and properties of MNPs as afunction of core sizes and shapes, ligand chemistry, solvent properties,and externalfield. We demonstrate the use and effectiveness of themodel by simulating the self-assembly of oleic acid ligand-function-alized magnetite (Fe3O4) nanoparticles, with spherical and cubicshapes, into rings, lines, chains, and clusters under a uniform external magneticfield. We found that the long-range electrostaticinteractions can favor the formation of a chain over a ring, the ligands promote MNP cluster growth, and the solvent can reduce therotational diffusion of the MNPs. The algorithm has been parallelized to take advantage of multiple processors of a moderncomputer and can be used as a plugin for the popular simulation software LAMMPS to study the behavior of small MNPs and gaininsights into the physics and chemistry of different magnetic assembly processes with atomistic details.

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