### About

Modern computational chemistry strives to provide an atomistically detailed dynamical description of fundamental chemical processes. The strategy for reaching this goal generally follows a two-step program. In the first step, electronic structure calculations are used to obtain the force fields that the nuclei are subject to. In the second step, molecular dynamics simulations are used to describe the motion of the nuclei. The first step is always based on quantum mechanics, in light of the pronounced quantum nature of the electrons. However, the second step is most often based on classical mechanics. Indeed, classical molecular dynamics simulations are routinely used nowadays for describing the dynamics of complex chemical systems that involve tens of thousands of atoms. However, there are many important situations where classical mechanics cannot be used for describing the dynamics. Our research targets the most chemically relevant examples include:

(1) Linear and nonlinear vibrational and electronic spectroscopy. The transition frequencies in these cases are often much larger than kT. Furthermore, in the spectral signals can be expressed in terms of optical response functions that lack a well defined classical limit.

(2) Vibrational and electronic relaxation. The quantum nature of the pathways of irradiative intramolecular energy redistribution within molecules and intermolecular energy transfer between molecules is attributed to the large gap between vibrational and electronic energy levels.

(3) Proton and electron transfer reactions. The elementary steps of many complex chemical processes are based on such reactions. Their pronounced quantum nature is attributed to the light mass of protons and electrons, which often gives rise to quantum tunneling and zero-point energy effects.

The challenge involved in simulating the quantum molecular dynamics of such systems has to do with the fact that the computational effort involved in solving the time-dependent Schrödinger equation is exponentially larger than that involved in solving Newton’s equations. As a result, a numerically exact solution of the Schrödinger equation is not feasible for a system that consists of more than a few atoms. The main research thrust of the Geva group is aimed at developing rigorous and accurate mixed quantum-classical, quasi-classical and semiclassical methods that would make it possible to simulate equilibrium and nonequilibrium quantum dynamics of systems that consist of hundreds of atoms and molecules. We put emphasis on applications to experimentally-relevant disordered complex condensed phase systems such as molecular liquids, which serve as hosts for many important chemical processes. We also specialize in modeling and analyzing different types of time resolved electronic and vibrational spectra that are used to probe molecular dynamics in those systems, often in collaboration with experimental groups.

###### Representative Publications

Hanna G. and Geva, E. (2008) “A computational study of the one and two dimensional infrared spectra of a vibrational mode strongly coupled to its environment: Beyond the cumulant and Condon approximations” J. Phys. Chem. B 112, 12991

Hanna, G. and Geva, E. (2008) “Vibrational energy relaxation of a hydrogen-bonded complex dissolved in a polar liquid via the mixed quantum-classical Liouville method” J. Phys. Chem. B 112, 4048

Shang, J. and Geva, E. (2007) “A computational study of a single surface-immobilized two-stranded coiled-coil polypeptide” J. Phys. Chem. B 111, 4178

Ka, B.J. and Geva, E. (2006) “Classical vs. quantum vibrational energy relaxation pathways in solvated polyatomic molecules” J. Phys. Chem. A 110, 13131

Ka, B.J. and Geva, E. (2006) “A nonperturbative calculation of nonlinear spectroscopic signals in liquid solution” J. Chem. Phys. 125, 214501

Ka, B.J. and Geva, E. (2006) “Vibrational energy relaxation of polyatomic molecules in liquid solution via the linearized semiclassical method” J. Phys. Chem. A 110, 9555-9567

###### Research Areas(s)

- Computational/Theoretical Chemistry

Materials Chemistry

Physical Chemistry

Ultrafast Dynamics