## Electronic properties of materials far from equilibrium

We develop general theories and perform computations to understand electronic properties of materials (e.g. semiconductors and molecules) driven far from equilibrium by lasers.

A current project is to understand the optical properties of laser-dressed materials. The main challenge for this project is that we cannot directly use the linear response theory that is defined for systems in thermal equilibrium because, for laser-driven materials, the strong laser-matter interaction drives the system constantly far from equilibrium.

## Decoherence in open quantum systems

We aim to develop general theories and exact numerical simulations (using hierarchal equations of motion method) to understand decoherence dynamics of systems interacting with Markovian, non-Markovian environments.

In a recent paper [J. Phys. Chem. Lett., 8, 4289-4294 (2017)], we construct a theory that shows that the physics behind the early-time loss of coherence is *fluctuations*.

**Electronic decoherence in molecular systems**

Among the decoherence processes, electronic decoherence in molecular systems and condensed phase environments is of ubiquitous importance that influences lots of chemical processes such as electron transfer and energy transfer, photochemistry, photophysics, etc.

## Excited state molecular quantum dynamics

Methodology development for adiabatic and non-adiabatic quantum dynamics which incorporates nuclear quantum effects but is also scalable to large molecular systems.

## Wavepacket dynamics

Developing efficient numerical methods to solve the time-dependent Schrodinger equation. We focus on the following ideas:

(i) Quantum trajectory methods – Based on the hydrodynamic formulation of quantum mechanics (i.e. de Broglie-Bohm mechanics), one can recast the quantum dynamics with quantum trajectories. These trajectories are just like classical trajectories except that they are coupled with each other through the so-called quantum potential.

(ii) Moving Gaussian wave packets – In order to represent the nuclear wavefunction, one can use a set of Gaussian wave packets. These Gaussian wave packets can move like classical trajectories, and provide a convenient basis to approximate the time-dependent wavefunction.