Multiscale Simulation of Quantum Nanosystems: Plasmonics of Silver Particles

Quantum nanosystems involve the coupled dynamics of fermions or bosons across multiple scales in space and time. Examples include quantum dots, superconducting or magnetic nanoparticles, molecular wires, and graphene nanoribbons. The number 10³ to 10⁹ of electrons in assemblies of interest here presents a challenge for traditional quantum computations. However, results from deductive multiscale analysis yield coarse-grained wave equation that capture the longer-scale quantum dynamics of these systems; a companion short-scale equation is also developed that allows for the construction of effective masses and interactions involved in the coarse-grained wave equation. The theory suggest an efficient algorithm for simulating quantum nanosystem which is implemented here. A variational Monte Carlo method is used to simulate the co-evolution of long- and short-scale processes. The approach does not require experimental data for calibration. It is validated via experimental data and TDDFT predictions on the nanoparticle size dependence of the plasmon spectrum.