A new density functional approach that employs both short and long range, rotationally invariant, multi-point particle interactions will be presented. This formalism will be shown to unify several closely connected phase field crystal (PFC) theories that have appeared in recent years, which are known for coupling important physics emergent at the atomic scale with diffusive kinetics governing microstructure evolution in most materials. Simulation results will be presented that demonstrate the interaction between nano--meso scales in PFC modelling of microstructure evolution. Specifically, recent studies of two-step nucleation in solidification, and cavitation in liquid pools during rapid cooling will be discussed. A formalism for coupling the PFC density order parameter to heat transfer will also be presented and shown to capture density rearrangement effects in latent heat release during solidification. We end by presenting a coupling of the PFC order parameter to electrical potential, and show results predicting void formation and time to failure in electromigration in polycrystalline materials.