Since joining KSU, I have been working on development and application of computational chemistry methods to study structure and dynamics of molecules in gas-phase and in condensed-phase, namely protonated water clusters H+(H2O)n and OH-(H2O)n, and small fragments N2H+, N4H+, CH3OH+ relevant to atmospheric chemistry. The bottleneck of such computer approaches is an evaluation of an interaction potential. Accurate ab initio methods are often too time-consuming to obtain structural and dynamical parameters. Therefore, orbital free methods gain in popularity. I am using MP2 (many-body perturbation method to the second order) and DFT methods (density functional theory) to calculate and assign vibrational spectra of gas phase molecules. These methods are still very time consuming even for small size molecules. To improve computer efficiency and circumvent expensive “direct” molecular dynamics calculations, an evaluation of the interaction potential “on the fly” can be replaced by using analytical form of the interaction potential. Many potentials are now available in the literature. I am in a process of extending my existing direct molecular dynamics codes to enable using any analytical potential energy surfaces.
I am interested to develop new methods to study structure and dynamics of molecular clusters; modify previously developed driven molecular dynamics to study complex vibrational spectra. Multi-dimensional infrared spectroscopy is considered to be a viable tool to study molecular structure and dynamics of complex molecules in the condensed phase. By extending the spectral information of a sample, spectral analysis is simplified and resolution is enhanced. 2D IR spectroscopy requires multiple IR pulses having the well-defined spectral bandwidth, phase, and amplitude. From such an experiment, vibrational spectra are spread into a number of dimensions, and the coupling between modes at different spatial locations can be determined. I will develop and test the “pump-probe” algorithm to collect and analyze vibrational spectra.
Computational tools allow describing properties of molecules beyond the harmonic approximation, such as proton transfer, the coupling between vibrational modes, understanding vibrational energy transfer dynamics, vibrational excitation/relaxation processes. To assess the accuracy and feasibility of the computational approach, I will perform benchmark calculations of small molecules by comparing the theoretical results and available experimental measurements.
At all stages of this project, undergraduate/graduate students can be engaged. Students will learn the computational methods, visualization tools, run simulations, and analyze results.