Molecular dynamics with nuclear quantum effects: merging the quantum and classical domains

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Sophya Garashchuk of the University of South Carolina is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop theoretical and computational approaches that consider the behavior of the nuclei in molecules and materials. This research is motivated by the need to understand nanomaterials and large molecular structures. In-depth understanding of how such structures and materials interact with light, current and heat in applications such as electronics, batteries and medical devices requires theoretical and computational methods capable of spanning several orders of magnitude in time, space, and hierarchy. Professor Garashchuk's research starts at the most fundamental level possible, for example, by examining protons. The more advanced computational descriptions (quantum calculations) that are restricted to just a few atomic nuclei at a time due to computational cost are merged with simpler classical representations for more complex, bigger and heavier nuclei. The atomistic simulations yield experimentally relevant properties such as predictions of the speed of the reaction or charge and energy transport rates. These parameters are necessary for the development of even more advanced models of bigger molecular systems. Modeling the systems’ properties and responses to external stimuli (temperature, electric and magnetic fields) guides the experiments and accelerate the development of new materials and molecular devices for sensing, computing, communications and other applications. Professor Garashchuk's research and educational activities will train the workforce ready for the emerging quantum information science. She promote use of computational chemistry and computing in education and research among students and researchers at her home institution, as well as at sister campuses and predominantly undergraduate institutions throughout the state of South Carolina. The research team is engaged in K-12 science demonstrations to showcase molecules and their roles in everyday technologies. These activities broaden participation of underrepresented groups in research, develop of the next-generation technologies, and communicate contributions of STEM to the general public of South Carolina, a geographically underrepresented group in the global research enterprise.Garashchuk develops theory and computational methods for the hierarchical treatment of nuclei practical for large (10-1000 atoms) molecular systems. The hierarchy consists of exact (time-dependent bases) and approximate methods (classical dynamics, possibly, with quantum corrections) unified by the trajectory framework. The exact quantum dynamics employs Gaussian bases which adapt to the evolving nuclear wave function by following the probability density flow, which follows the quantum trajectories. Such basis function evolution defines ‘minimalistic’ representation of a wavefunction in configuration space and improves the scaling properties of the method with the system size. The Gaussians are correlated and normalizable by construction. The multilevel description of the nuclei, helps to exploit the time- and mass-scale separation for an efficient computational methodology, interfaced with on-the-fly electronic structure calculations. The Quantum Trajectory-guided Adaptable Gaussian (QTAG) dynamics is employed to study nuclear quantum effects in molecular aggregates, i. e. crystalline materials, active sites of enzyme catalytic cycle, functional molecules integrated into covalent and metal-organic frameworks, as a way to tune and control their properties relevant to the design of molecular sensors, switches, catalysts, and to the emerging quantum device and computer applications. Connecting research with education and workforce development, Garashchuk incorporates computational chemistry into the graduate and undergraduate curriculum, by providing cyber-research opportunities to regional undergraduate colleges, and by hands-on training of students at all levels in computational chemistry tools and methods.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.