The research goal of the Prezhdo group is to obtain a theoretical understanding at the molecular level of chemical reactivity and energy transfer in complex condensed-phase chemical and biological environments. This requires the development of new theoretical and computational tools and the application of these tools to challenging chemical problems in direct connection to experiments.
Quantum mechanics, in principle, may be used to describe any chemical process. Its application to systems containing more than a dozen atoms, however, is nearly impossible due to computational constraints. Classical mechanics, on the other hand, may be easily applied to systems of thousands of atoms. Fortunately, in a given chemical system, only a small subset of the particles involved must be treated quantum-mechanically. This has allowed our group to develop a number of mixed quantum-classical approaches that are suitable for different situations. Quantized Hamilton Dynamics, for example, provides a beautiful and remarkably simple extension of classical mechanics that incorporates zero-point motion, tunneling, dephasing and other quantum effects. The Stochastic Mean Field approach deals with chemical reactions involving quantum transitions, such as absorption and emission of light, and conversion of light and electric energy to forming and breaking chemical bonds. Chemical versions of the Schrodinger Cat paradox, the “watched pot never boils”, and quantum Zeno effects are other important phenomena that may be modeled with the Stochastic Mean Field approach. The Bohmian or hydrodynamic interpretation of quantum mechanics is used to couple quantum and classical variables and to interpret results in terms of intuitive particle trajectories. These varied quantum-classical approaches are being implemented within the framework of time-dependent density functional theory.
The Prezhdo group pioneered ab initio real-time simulations of the ultrafast electron transfer across the molecule-semiconductor interface that drives Gratzel-type solar cells. Organic-inorganic interfaces are critical in molecular electronics and remain the field’s least understood components. We have established electron-transfer mechanisms that suggest ways to improve solar cell efficiencies. Motivated by recent experiments, we are modeling charge dynamics in semiconductor and metallic nanoparticles, carbon nanotubes and nanoribbons, and related nanoscale systems. Time-domain atomistic simulations of interactions between charges, spins and phonons in these materials create the theoretical basis for photovoltaic devices, optical and conductance switches, quantum wires, logic gates, miniature field-effect transitions and lasers.
Our group has developed the simplest and most used model of biological catch-binding, a fascinating biological phenomenon whereby the application of a pulling force increases bond lifetime (!). We created a physically intuitive description of catch-binding and derived universal laws that unite experimental data obtained through different pulling regimes. We are investigating the atomic origin of catch-binding by steered molecular dynamics and study other counter-intuitive force-induced effects in molecular biology, such as force-induced allostery.
New generations of electro-optic devices based on polymers showing order-disorder transitions are being designed by colleagues in Chemistry and Chemical Engineering. Our group developed a statistical-mechanical model of the ordering that clearly explains how the efficiency of the polymeric materials depends on molecular structure, temperature, electric field and other tunable parameters.
Members of the Prezhdo group use both pen-and-paper and computers in their research.