Session M02: JCP-DCP Editors Choice

Integrating Electronic and Nuclear Quantum Effects via the Nuclear-Electronic Orbital Approach

Nuclear quantum effects such as zero point energy, nuclear delocalization, and tunneling play an important role in a wide range of chemical and biological processes. The incorporation of nuclear quantum effects and non-Born-Oppenheimer behavior into quantum chemistry calculations and molecular dynamics simulations is a longstanding challenge. To address this challenge, the nuclear-electronic orbital (NEO) approach treats specified nuclei, typically protons, quantum mechanically on the same level as the electrons with multicomponent density functional theory (DFT) or wave function methods. 1-3 This approach inherently includes nuclear delocalization and zero-point energy in molecular energy calculations, geometry optimizations, reaction paths, and dynamics. It can also provide accurate descriptions of excited electronic, vibrational, and vibronic states, as well as nuclear tunneling and nonadiabatic dynamics. The real-time NEO methods enable nonequilibrium nuclear- electronic dynamics simulations beyond the Born-Oppenheimer approximation for the investigation of excited state chemical reactions. This talk will provide an overview of the foundational NEO methods as well as applications to photoinduced proton transfer and hydrogen tunnelling processes.   

Quantum dynamics in molecular systems: Theory and applications to intramolecular singlet fission

The accurate theoretical treatment and simulation of dynamical processes in many-body quantum systems is a long-standing goal in chemical and condensed matter physics. In this talk, I will discuss recent work in this field, focusing on time-dependent multiconfiguration methods. Formulated in the form of a tensor network, these variational basis-set methods facilitate accurate simulations of quantum dynamics in systems with many degrees of freedom. Applications of the methodology to photoinduced molecular processes are presented, including charge transport and singlet fission, a multiple exciton generation process in molecular materials. Considering specifically intramolecular singlet fission in pentacene dimers with different linker groups, the mechanisms of this photophysical process are analyzed, in particular the role of the involved electronic states and the effect of electronic-vibrational coupling. It is shown that the formation of the multiexciton state, corresponding to the first step of the singlet fission process, occurs mainly through a superexchange-like mechanism involving charge transfer states and is facilitated by vibronic coupling.   

Ultrafast Vibrational Dynamics for Molecular Polariton Chemistry

Molecular vibrational polaritons are hybrid half-light, half-matter quasiparticles. Because of their hybrid photon-matter characters, it has been shown that polaritons can modify molecular potential enrgy landscapes and therefore chemical reactions. Using pump-probe and 2D IR spectroscopy to study vibrational-polaritons, we learned interesting dynamics that shed light to polariton chemistry.

In this talk, I will briefly introduce the principles of using pump probe and 2D IR spectroscopy to follow polariton dynamics, and overview a few ultrafast phenomena of molecular vibrational-polaritons due to their hybridized nature: 1.  Cavity-enabled intermolecular energy transfer,  2. Polariton accelerated barrier crossing events, 3. Polariton coherence delocalization in spaces. These results will have significant implications in new polariton chemistry and polariton based quantum technologies.