In the Levine group we work on a variety of problems, ranging from applied chemistry and physics to method development to high performance computing. Below are brief discussions of several ongoing research projects in our group.
Excited State Dynamics of Nanomaterial
Due to their unique and tunable optical and electronic properties, nanomaterials show great promise for various photophysical applications, e.g. solar energy conversion (both photovoltaic and photocatalytic) and light emission. We develop and apply theoretical methods to understand the exchange of energy between electronic and nuclear degrees of freedom. Our goal is to predict how the microscopic structure of materials determines this exchange of energy, enabling the development of materials with desirable and well-controlled properties. See this review article for a detailed description of our work in this area.
Nonadiabatic Molecular Dynamics on Many Electronic States
The introduction of ab initio MD (AIMD) simulation methods resulted in a paradigm shift in the modeling of chemical dynamics on the ground and lowest few (<5) excited electronic states. Prior to AIMD, modeling reaction dynamics required advanced knowledge of and/or assumptions about the potential energy surfaces (PESs) determining those dynamics. In contrast, AIMD methods predict the relevant nuclear motions, electronic wave functions, and PESs via on-the-fly first-principles calculations. This enables simulation of chemical phenomena with minimal assumptions or prior knowledge. Many important chemical problems involve dense manifolds of electronic states, however, including optoelectronic and plasmonic materials, chemistry in strong laser fields, atmospheric chemistry, and radiation damage to molecules and materials. We are extending the capability of AIMD methods by developing practical approaches to accurately describe the entanglement between electronic and vibrational motions (decoherence) in systems with very large numbers of electronic states. See recent work in this direction here and here.
Graphics Processing Unit Computing
Graphics processing units (GPUs) are low-cost, high-performance computer processors designed for graphical applications (i.e. video games). Fortunately for scientists, both graphical rendering and quantum chemistry depend on the ability of the processor to perform fast floating point linear algebra operations. By taking advantage of this similarity, we are able to apply GPUs to accelerate quantum chemical calculations, with performance ranging from tens to hundreds of time faster than a traditional CPU core. Our work on nanomaterials and dense manifolds of electronic states are both enabled by high-performance implementations of electronic structure calculations for GPU hardware developed in our group. For example, see our work on GPU-accelerated time-independent and time-dependent electronic structure calculations.