Associate Professor of Chemistry
Ph.D. Wayne State University, 2003
Research in the Li group focuses on the development of low-scaling methods to resolve excited state properties of many-electron systems, both in the time and frequency domains. This work is complimented by, and finds uses in, the development of efficient methods for studying non-adiabatic dynamics in large-scale systems. Students will have a unique opportunity to participate in interdisciplinary research subjects.
The Born-Oppenheimer (BO) and extended Lagrangian (EL) trajectories are founded on the assumption that a single electronic potential surface governs the dynamics. Such adiabatic approaches are widely used in investigations of reactions on ground state surfaces. A major limitation of adiabatic trajectories is that they are not applicable to reactions involving nonadiabatic electronic processes, i.e., multiple potential energy surfaces. Proper incorporation of the electronic response is crucial for describing a host of dynamical processes, including laser induced chemistry, dynamics at metal or semiconductor surfaces, and electron transfer in molecular, biological, interfacial, or electrochemical systems. Recently, we introduced an efficient ab initio direct Ehrenfest dynamics algorithm within the TDHF and TDDFT approximations (J. Chem. Phys. 2005, 123, 084106). This approach integrates ab initio TDHF/TDDFT equation "on the fly." Electron dynamics is described within a non-adiabatic non-perturbative framework.
Geometry optimization is an essential part of computational chemistry. Any theoretical investigation that involves calculations of transition structures, barrier heights, heats of reaction, or vibrational spectra requires searches for one or more minima or saddle points on a potential energy surface (PES). Computational methods are applied to large systems of ever increasing size. Biomolecules, polymers and nanostructures with hundreds to thousands of atoms are often difficult to optimize because of excessive degrees of freedom. Any decrease in the computational cost and increase in the general stability of geometry optimization would be welcome. We are interested in developments of efficient optimization methods for both electron wave function and nuclear geometry. Our developments span from novel two electron integration methods and energy minimization schemes to advanced computer machinery including high performance parallelism and cost effective sparse matrix manipulations.
Our theoretical developments are being applied to studies of laser controls of molecular reactions, electron transfer at surfaces, nonadiabatic reactions in biological systems, and characterizations of magnetism in nanoparticles.
Fischer, S. A.; Lingerfelt, D. B.; May, J. W.; Li, X. “Non-adiabatic Molecular Dynamics Investigation of Photoionization State Formation and Lifetime in Mn2+-Doped ZnO Quantum Dots.” Phys. Chem. Chem. Phys. 2014, 16, 17507.
Ding, F.; Guidez, E.; Aikens, C.; Li, X. “Quantum Coherent Plasmon in Silver Nanowires: a Real-time TDDFT Study.” J. Chem. Phys. 2014, 140, 244705.
Lestrange, P. J.; Ding, F.; Peng, B.; Trucks, G. W.; Frisch, M. J.; Li, X. “Density of States Guided Second-Order Moller-Plesset Perturbation Theory.” J. Chem. Theory Comput. 2014, 10, 1910.
Goings, J. J.; Ding, F.; Li, X. “Accelerating Wavefunction Optimization using Quasi-Newton DIIS.” Adv. Quantum Chem. 2014, 68, 77-86.
Peng, B.; Van Kuiken, B. E.; Li, X. “A Guided Self-Consistent-Field Method for Excited State Wave Function Optimization: Applications to Ligand Field Transitions in Transition Metal Complexes.” J. Chem. Theory Comput. 2013, 9, 3933.
Chapman, C. T.; Liang, W.; Li, X. “Solvent Effects on Intramolecular Charge Transfer Dynamics in a Fullerene Derivative.” J. Phys. Chem. A 2013, 117, 2687.
Ding, F.; Van Kuiken, B.; Eichinger, B.; Li, X. “An Efficient Method for Calculating Dynamical Hyperpolarizabilities using Real-time Time-dependent Density Functional Theory.” J. Chem. Phys. 2013, 138, 064104.
Nguyen, P.; Ding, F.; Fischer, S. A.; Liang, W.; Li, X. “Solvated First-principles Excited State Charge Transfer Dynamics with Time-Dependent Polarizable Continuum Model and Solvent Dielectric Relaxation.” J. Phys. Chem. Lett. 2012, 3, 2898.