RUI: Computational Study of Vibrational Motion in Hydrogen-Bonded Systems

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The Chemical Structure Dynamics and Mechanism (CSDM-A) Program of the Chemistry Division supports Professor Martina Kaledin and her students at Kennesaw State University (KSU) to develop computational methods to study structure and properties of hydrogen-bonded systems. Water (H2O) is an example of a hydrogen bonded system. When hydrogen (H) atoms bond to oxygen (O) atoms, the H atom becomes partly positively charged, and the O atom partly negatively charged. In liquid water, the H2O molecules therefore tend to stick to each other because of the positive-negative attraction between H and O on different H2O molecules. Hydrogen bonding is actually a general feature of many molecules that contain O-H, or N-H (N= nitrogen) bonds as part of their structure. Hydrogen bonding is an important topic of research because it can cause the formation of large networks of molecules and influence the rates and outcome of chemical reactions. The effects of hydrogen bonding are not easy to predict, especially when many atoms and molecules are involved. Professor Kaledin has developed advanced computer models to simulate the behavior and properties of hydrogen bonded systems. She and her students are using high-performance computer systems (IBM HPC computer at KSU) are employed to predict the structure of hydrogen bonded systems as well as their response to light energy. Experimental chemists use what are called spectroscopic techniques to measure how light of different wavelengths (ultraviolet, visible, infrared) are absorbed by molecular systems. Prof. Kaledin is using computational approaches to predict experimental "spectra," which in turn helps experimental scientists understand their observations. The findings of this project are contributing to developing molecular dynamics simulation models which advance our understanding of many chemical systems, as well s complex biological systems. The researchers involved in this project include both undergraduate and graduate students. They are learning principles of supercomputing, molecular modeling, supercomputing, interpretation of vibrational spectra, analyzing the energetics of chemical reactions, and molecular visualization techniques. Prof. Kaledin is also Integrating elements of this research project into her formal undergraduate courses, with the aim to improve science education and STEM students success.Central to these tasks is to calculate and assign vibrational spectra using driven molecular dynamics (DMD). In the DMD method, an external sinusoidal electric field, representing a continuous wave (CW) laser pulse, is used to scan the spectrum for resonances and obtain an absorption profile. The strength of the external field determines the intensity of the motion. The important feature of DMD is the ability to study the anharmonic motion and mode coupling, and make assignments. At resonant frequencies, the molecular motions induced by weak driven force correspond to the normal-mode frequencies, while harder driving induces anharmonic motion. To identify resonant frequencies, the average internal energy of the molecule is obtained after a finite time of driving. DMD is also easily expandable to two-dimensional spectroscopy, such as 2D-IR, an even more powerful tool for studying complex dynamical structures. These techniques provide detailed dynamic information on protonated water clusters and small molecules relevant to atmospheric chemistry, reveal their stability and timescale of motion of individual groups of atoms. The students involved in this project are being trained in molecular dynamics simulations, ab initio and density functional theory calculation, and interpretation of Raman and infrared spectra (including 2D IR). All of these tools and skills are highly valuable for scientists entering the modern workforce. In addition to advancing other areas of science through the computational models developed in this project, the broader impacts of this work is includes the promotion of strong interactions between the research community and industry, and outreach to students from disadvantaged backgrounds or underrepresented groups, for example through engagement with the Peach State Louis Stokes Alliances for Minority Participation (LSAMP).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.