The unique and tunable properties of plasmonic nanostructures make them appealing building blocks for materials for energy conversion, sensing, and imaging. These applications are made possible by the capacity of plasmonic nanostructures to localize light energy, to interact nonlinearly with the light field, and to convert energy between light, electronic excitations, and nuclear motions at ultrafast timescales. The ability to rationally design materials to control these light-matter interactions would revolutionize these fields. Such rational design will require a microscopic understanding of coupled electronic and nuclear motions in a radiation field. It is therefore essential to develop theoretical and computational tools capable of accurately and efficiently simulating such motions in nanoscale systems.