Abstract
An extended molecular dynamics simulation that incorporates classical free electron dynamics in the framework of the force-field model has been developed to enable us to describe the optical response of metal materials under the visible light electric field. In the simulation, dynamical atomic pointcharges follow equations of motion of classical free electrons that include Coulomb interactions with the oscillating field and surrounding atomic sites and collision effects from nearby electrons and ions. This scheme allows us to simulate an interacting system of metals with molecules using an ordinary polarizable force-field and preserves energy conservation in the case without applying an external electric field. As the first applications, we show that the presented simulation accurately reproduces (i) the classical image potential in a metal-charge interaction system and (ii) the dielectric function of bulk metal. We also demonstrate (iii) calculations of absorption spectra of metal nano-particles with and without a water solvent at room temperature, showing reasonable red-shift by the solvent effect, and (iv) plasmon resonant excitation of the metal nano-particle in solution under the visible light pulse and succeeding energy relaxation of the absorbed light energy from electrons to atoms on the metal and to the water solvent. Our attempt thus opens the possibility to expand the force-field based molecular dynamics simulation to an alternative tool for optical-related fields.
Highlights
Force-field based classical molecular dynamics (MD) simulations are fundamental computational techniques to describe timeevolutions of molecules and materials from the atomic level.1,2 The techniques have been widely used for analyses of, for examples reaction dynamics, structural change, fracture, free energy, and vibrational spectroscopies.3–6 Further developments have been attempted to be accurate and expand their applications.One of the important directions of development of the molecular simulations is to take into account a change in the electronic state overcoming the traditional fixed point-charge model in the forcefield
We develop a classical electronic and molecular dynamics (CEMD) simulation method for metallic materials, where equations of motion of the free electrons are embedded in the framework of the molecular simulation
We show that the CEMD calculation of the static metal–ion interaction system reproduces the classical image charge potential
Summary
Force-field based classical molecular dynamics (MD) simulations are fundamental computational techniques to describe timeevolutions of molecules and materials from the atomic level. The techniques have been widely used for analyses of, for examples reaction dynamics, structural change, fracture, free energy, and vibrational spectroscopies. Further developments have been attempted to be accurate and expand their applications. In contrast, electromagnetic analyses of mesoscopic or macroscopic systems have been carried out by numerically solving the Maxwell’s equations or analytical equations based on the electromagnetism, where materials are given as the continuum model with dielectric functions or polarizability on each spatial grid cell or hydrodynamic expression.44 These approaches, have limitations in their applicability. We develop a classical electronic and molecular dynamics (CEMD) simulation method for metallic materials, where equations of motion of the free electrons are embedded in the framework of the molecular simulation This approach enables us to calculate interaction among electrons and atoms of the metal and solvent molecules under the light oscillating electric field with relatively low computational cost.
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