Multiscale Simulation on a Light-Harvesting Molecular Triad

We have investigated the effect of solvation and confinement on an artificial photosynthetic material, carotenoid-porphyrin-C$_{60}$ molecular triad, by a multiscale approach and an enhanced sampling technique (Replica Exchange Method). We have developed a combined approach of quantum chemistry, statistical physics, and all-atomistic molecular dynamics simulation to determine the partial atomic charges of the ground-state triad. The confinement effects on the triad were modeled by imposing three sizes of spherocylindrical nanocapsules. The triad is structurally flexible under ambient conditions and its conformation distribution is manipulated by the choice of water models and confinement. Two types of water models (SPC/E and TIP3P) are used for solvation. We have shown that a slight structural difference in the two water models with the same dipole moment can have great distinction in water density, water orientation and the number of hydrogen bonds in the proximity of a large flexible compound such as the triad. Subsequently, it has direct impact on the position of the triad in a confinement as well as the distribution of conformations at the interface of liquid and solid in a finite-size system.