Our research program can be divided into two main areas:

1. Development of mixed quantum-classical dynamics methodologies

Simulating the quantum dynamics of quantum processes occurring in systems containing large numbers of particles is computationally expensive. In such cases, one must resort to semi-classical and mixed quantum-classical techniques in order to significantly reduce the computational costs. In our group, we focus on mixed quantum-classical methods, which treat the subsystem of interest quantum mechanically and the particles in its environment (or bath) in a classical-like fashion. For example, the subsystem could be a chromophore or a key proton/electron in a charge transfer reaction, while the environment could be a molecule or a solvent.

Over the past few decades, a host of mixed quantum-classical dynamics techniques have been developed, which essentially differ in the way they treat the coupling between the subsystem and bath. As a result, each method has its own regime of validity. Typically, these methods struggle in capturing decoherence effects, satisfying detailed balance, generating accurate long-time dynamics, and dealing with strong subsystem-bath coupling. One approach, known as Mixed Quantum-Classical Liouville (MQCL) dynamics, is recognized as being one of the most accurate approaches, but its practical implementation has proven to be highly computationally challenging. In our group, we are looking for ways to reduce these computational challenges without adversely affecting the accuracy. In addition, we are interested in developing new ways of performing MQCL dynamics, which aim to circumvent the aforementioned challenges altogether.

2. Quantum transport of charge and energy

The transport of protons, electrons, and energy plays an instrumental role in many chemical and biological phenomena such as hydrogen bonding, enzyme catalysis, photochemistry, and photosynthesis, and in energy conversion devices such as electrochemical and photovoltaic cells. A fundamental understanding of these processes may be achieved through theoretical studies of their underlying molecular dynamics. Often, these processes are inherently quantum mechanical in nature, so any efforts made towards modeling them should take this into account. In addition, these processes usually take place in systems containing large numbers of atoms. Therefore, to significantly cut down the computational costs, one can treat a small number of particles directly associated with the transport quantum mechanically, while the remaining particles can be treated in a classical-like fashion.

Our interest is to apply mixed quantum-classical approaches for simulating the dynamics of a variety of charge and energy transfer processes in chemical and biological systems of fundamental and technological importance (e.g., proton transfer, photo-induced electron transfer, proton-coupled electron transfer, vibrational energy transfer, heat transport, electronic energy transport), and thereby shed light on ways of controlling them to improve the performance of solar energy harvesting materials, catalysts for water splitting and solar fuels production, and molecular electronics devices. Specifically, we are interested in control methods, which rely on varying the properties of the classical part of the system, or coupling the quantum part to laser fields whose properties can be easily tuned. The results of these studies will ultimately lead to principles for designing devices that can reduce the world’s dependence on fossil fuels or be used in the electronics industry.