Quantum Chemistry of Extended Molecular Aggregates

Challenges

Exploring biological phenomena at molecular scale is oftentimes indispensable to develop new drugs and intelligent materials. Most of relevant system properties are affected by intermolecular interactions with nearby environment such as solvent or closely bound electronic chromophores. Studying molecular aggregates requires rigorous and accurate Quantum Chemistry methods, the computational cost of which grows extremely fast with the number of electrons in the system. Therefore, it is of particular importance to develop mathematical models to simplify equations and implement them in a form that is relatively cheap but still provides high accuracy and reliability.

The Project

This Project focuses on finding a unified way to simplify various equations of Quantum Chemistry of extended molecular systems, i.e., molecular aggregates such as interacting chromophores and molecules solvated by water and other solvents. Indeed, one of the important difficulties encountered in Quantum Chemistry of large systems is the need of evaluation of special kind of numbers known as electron repulsion integrals, or in short, ERIs. In a typical calculation, the amount of ERIs can be as high as tens or even hundreds of millions (!) that unfortunately prevents from application of conventional methods when the number of particles in question is too large. In the Project, the complicated expressions involving ERIs shall be greatly simplified to reduce the computational costs as much as possible while introducing no or minor approximations to the original theories.

The generalized effective one-electron potentials (EOPs), developed in the Project, will be utilized for two important fields of Quantum Chemistry. First Project is related to the energy transfer at the very short distances between molecules that are present in molecular factories used by nature in the process called photosynthesis. In that process, chemical energy is produced directly from sunlight, water and carbon dioxide. Understanding photosynthesis is of key importance in designing novel materials that can absorb sunlight with very high efficiency. Second, the Project will study special kind of repulsive forces occurring between molecules, as well as small deformation of molecular shapes in the presence of other molecules. These aspects can be helpful in developing new methods to perform accurate simulations of how molecules move in nature, or in other words, what is their dynamics.

Our philosophy

In our research group we follow the notion of the importance of the one-electron operators in Quantum Chemistry, emphasised in the Density Functional Theory itself. Our goal is to create ab-initio approach of molecular reality that maximally utilizes the above paradigm.