Even for large systems, there are plenty of situations where quantum dynamical effects are known to be important-and therein lies the challenge. For example, the study of hydrogen transfer in proteins is important for understanding the multitude of biological functions supported by this fundamental reaction-which in some cases even requires consideration of deep proton tunneling. Similarly, hydrogen tunneling dynamics was experimentally revealed in phenol-ammonia clusters activated by UV-photon absorption. Other aromatic biomolecules (e.g., indole and pyrole 3 in the presence of water and ammonia solvents) manifest a behavior that attests to quantum nuclear effects governing the dynamics in excited electronic states. These examples serve to highlight the importance of considering nuclear quantum effects, combined with multiple electronic states when necessary, that cannot be taken into account using only classical trajectories.