Optical forces, torques and force densities calculated at a microscopic level using a self-consistent hydrodynamics method

The calculation of optical force density distribution within a material is challenging at the nanoscale, where quantum and non-local effects emerge and macroscopic parameters such as permittivity become ill-defined. We demonstrate that the microscopic optical force density of nanoplasmonic systems can be defined and calculated using a self-consistent hydrodynamics model that includes quantum, non-local and retardation effects. We demonstrate this technique by calculating the microscopic optical force density distributions and the optical binding force induced by external light on nanoplasmonic dimers. We discover that an uneven distribution of optical force density can lead to a spinning torque acting on individual particles.