Atomistic simulation of agglomeration of metal nanoparticles considering the induced charge density of surface atoms

To simulate the agglomeration of nanoparticles subjected to an external electric field, we develop a method to calculate the induced charge density in surface atoms to account for the inter-particle attractions between metallic nanoparticles, based on classical electrodynamics. A polarizable particle is subjected to dielectrophoresis force in a non uniform AC electric field. The induced charge density in a surface atom layer is redistributed to minimize the electric field inside the particle, restricting the total charge density of nanoparticles during the molecular dynamics simulations via a Lagrange multiplier method. The developed method is implemented in the LAMMPS code, where Lorentz and Coulomb forces applying on partially charged surface atoms are embedded to correct atomic motions in response to the applied AC electric field. In numerical examples, the electric field around a spherical nanoparticle shows good agreement with the analytical solution under external electric field. The proposed method is turned out to be more efficient for the problems of large particles since the ratio of surface to bulk atoms decreases as the size of particle increases. When an external electric field isexerted, the ordered aggregation of gold nanoparticles is observed in physical experiments and investigated through the LAMMPS simulations. The developed method successfully simulates that the nanoparticles are not only aligned in the direction of electric field but also formed lattice bonds due to the charges induced by the electric field.