Modeling Ultrafast Solvated Electronic Dynamics Using Time-Dependent Density Functional Theory and Polarizable Continuum Model Wenkel Liang, Craig T. Chapman, Feizhi Ding, and Xiaosong Li* Department of Chemistry, University of Washington, Seattle, Washington 98195, United States ABSTRACT: A first-principles solvated electronic dynamics method is introduced. Solvent electronic degrees of freedom are coupled to the time- dependent electronic density of a solute molecule by means of the implicit reaction field method, and the entire electronic system is propagated in time. This real-time time-dependent approach, incorporating the polarizable continuum solvation model, is shown to be very effective in describing the dynamical solvation effect in the charge transfer process and yields a consistent absorption spectrum in comparison to the conventional linear response results in solution. I. INTRODUCTION Many chemical and physical processes involving multiple potential energy surfaces require nonperturbative treatment of electronically nonadiabatic dynamics. A few examples include laser-controlled molecular reactions, determining lifetimes of excited states on particular surfaces, interfacial charge transfer dynamics, surface-enhanced chemical processes, and excitonic dynamics in nanocrystalline materials. Of particular interest is the dynamics of atoms and molecules in solution, where solvation effects can change fundamental physical properties of the solute, drastically alter the outcome of chemical reactions, and either prevent or enhance the formation of certain macrostructures. Many factors can play a role in guiding the outcome of a reaction including solvent size, polarity, and response time, as well as the behavior of the solute as it adapts to the fluctuations in the solvent environment. Furthermore, solvents have been known to have a considerable impact on the stabilization of molecular electronic structures and dynamics, particularly states with strong permanent dipole moments, a characteristic of charge-transfer (CT) states, 1,2 as well as chemi- cal reaction rates due to the introduction of additional free energy of solvation. To better simulate the class of electronic dynamics taking place in the solution phase, the inclusion of solvent effects is always desirable and critically important for an accurate description. The most direct way to describe the composite solute- solvent system is to explicitly include solvent molecules and evaluate the state of the system by means of molecular mech- anics (MM), 3,4 quantum mechanics (QM), or a combination thereof. 5-7 In such cases, the time dependence of the solvent polarization is obtained explicitly from the simulated traje- ctories in solute-solvent molecular dynamics (MD). A less computationally demanding and more flexible approach uses the implicit solvation model. In this model the polarization is determined by the dielectric function of the solvent, described as a continuous medium in which a cavity hosts the solute. Continuum models developed to treat the time-dependent solvation response can be generally categorized into two main classes. The first introduces a separation of the solvent pola- rization into a dynamical contribution described by the optical dielectric constant, associated with the solute’s electronic motion, and an inertial or orientational contribution, related to its nuclear motion and the bulk dielectric permittivity. 8-11 The response of the solvent is described in terms of these two contributions, and typically the dynamical component is assumed to equilibrate instantaneously to the final state in the presence of the inertial part of the polarization, while the orientational component of the polarization remains in equilibrium with the charge density of the initial state. On the other hand models of the second class implicitly consider dynamical and inertial effects in a single response, 12-15 as the transition is represented as a step-like change in the solute charge density, and the solvent response is modeled by introducing the complex dielectric permittivity as a function of the frequency. In order to include solvent effects within solute ultrafast electronic dynamics the method presented herein employs a polarizable continuum model and is developed according to the following strategy: the solvent electronic response is treated as a dynamical quantity, whose change comes instantaneously as a result of motion in the electronic degrees of freedom of the solute molecule. We incorporate a continuum representation of Received: December 22, 2011 Revised: January 24, 2012 Published: January 25, 2012 Article pubs.acs.org/JPCA © 2012 American Chemical Society 1884 dx.doi.org/10.1021/jp2123899 | J. Phys. Chem. A 2012, 116, 1884-1890