This thesis explores the application of electronic structure methods, particularly Frozen-Density Embedding Theory (FDET), within the context of multiscale modeling. FDET divides systems into chemically relevant subsystems, enabling efficient yet precise quantum mechanical treatment. The theoretical framework is elucidated, covering quantum mechanical methods, molecular mechanics, and the formalism of FDET. Practical applications investigate the polarisation of environments for excited states and dynamics of electric field gradients in various solvated systems. Additionally, a computational protocol for electric field gradient calculations within FDET is proposed, significantly reducing computational costs while maintaining accuracy.