Molecules in Non-Perturbative Fields: Improving Time-Dependent Density Functional Approximations and Electron-Ion Correlation Methods

Neepa Maitra of CUNY Hunter College is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop theoretical and computational approaches for simulating the correlated dynamics of electrons and ions. The Condensed Matter and Materials program in the Division of Materials Research also contributes to this award. Understanding the motion of electrons and ions is important for understanding and predicting many phenomena that involve the interaction of matter with light. These phenomena have both fundamental and technical importance, for example, photovoltaic devices which convert light into electricity, photocatalysis, and control of chemical processes using lasers. The equation that governs this motion has been known for 90 years. For all but the simplest systems, however, it is too difficult to solve this equation exactly. This difficulty arises because of correlated motion. Each electron's motion affects every other electron's motion as well as each ion's, and vice-versa. Time-dependent density functional theory (TDDFT) is an efficient, approximate and popular approach to solving this equation. In many cases, the particular approximations used today are not adequate, causing unpredictable errors in the electron dynamics. Maitra and her coworkers develop improved approximations based on rigorous theoretical considerations. Both undergraduate and graduate students participate in this cutting-edge research. Maitra organizes mini-workshops at CUNY open to scientists in the wider New York area. She works with existing programs at Hunter College to promote the development of underrepresented minority scientists Maitra and her coworkers develop improved, robust approximations for electron dynamics by imposing exact conditions, so that the theory can be used for real-time dynamics with as much confidence and predictability as density functional theory is used for ground-state energies and structures. The goals is to overcome several limitations of TDDFT that currently prevent it from being used reliably for real-time electron dynamics in the non-perturbative regime, as well as for excitation spectra. The dynamics of the electrons and ions are coupled by using a method based on the recently-introduced first-principles exact factorization approach. This includes developing practical mixed quantum-(semi)classical schemes for correlated electron-ion dynamics that include electronic decoherence and wave packet-branching from first-principles.