Research

Li Research Group

We are an electronic structure theory group focused on the development of time-dependent electronic structure theory, relativistic quantum mechanical techniques, and new methods for studying non-adiabatic dynamics of large-scale systems. Visit the Research page for more information on the research being done in the Li group.

Time-Dependent Many-Body Theory and Quantum Electronic Dynamics

The time-dependent Schrödinger and Dirac equations govern all non-equilibrium quantum mechanical processes of a many-electron system. Understanding these processes is crucial to many advanced scientific research and technological developments. One area of the research effort in the Li group focuses on the development of time-dependent many-electron theories and computational methods that can be applied to . . .

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Relativistic Electronic Structure Theory

For many molecules, such as those containing heavy elements, the non-relativistic Schrodinger equation is no longer valid. To go beyond the Schrodinger equation, we are developing methods based off variational treatments of the relativistic Dirac equation. This allows us to accurately treat relativistic interactions, such as spin-orbit coupling, for molecular systems. In particular, we are . . .

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Low-Scaling Electronic Structure Theories and Optimization Algorithms

The size of systems being investigated using the tools of quantum chemistry is ever increasing. Discerning the equilibrium conformations of biomolecules, polymers and nanostructures with hundreds to thousands of atoms is often computationally demanding due to the nonlinear scaling of computational difficulty with respect to the number of electronic and nuclear degrees of freedom. Methods . . .

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First-Principles Nonadiabatic Dynamics

Another active development area in the Li research group focuses on accurately reproducing chemical dynamics for a wide range of system sizes and time scales. To this end, we develop efficient numerical schemes to simultaneously integrate the quantum and classical equations of motion for all or some subset of the nuclear, electronic (spatial and spin), . . .

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Real-Time Time-Dependent Dielectric Response

The time delay between photoexcitation of a solute and the electric polarization of the solvent is of enormous importance to the proper description of solvated excited state chemical dynamics. This out-of-phase dielectric response is responsible for the frequency dependence of dielectric media permittivities, and the dielectric relaxation/loss phenomenon. In conjunction with the real-time time dependent . . .

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X-Ray Spectroscopy and High-Energy Chemical Physics

X-Ray absorption spectroscopy (XAS) and transient X-Ray absorption (XTA) are complex spectroscopies offering a wealth of information about electronic and nuclear structure. They also remain a challenging problem for theorists. Electronic relaxation due to the core excitations, environmental effects, scalar and spin-orbit relativistic effects, and higher-order multipole coupling to the incident field all need to . . .

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Chemical Physics of Defects in Nanocrystals

Doping inorganic semiconductor quantum dots (QDs) with transition-metal ions introduces unique electronic, optical, and magnetic properties that are otherwise absent in the host semiconductor lattice. The potential to integrate room-temperature ferromagnetism with the electrical properties of semiconducting materials makes these so-called diluted magnetic semiconductors (DMSs) attractive for spin-electronic and spin-photonic applications. Our recent advances have . . .

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