Development of Computational Methods and their Applications to Studying Nuclear Quantum Dynamics of Complex Molecular Systems

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Vladimir Mandelshtam of the University of California, Irvine, is supported by the by the Chemical Theory, Models and Computational Methods program in the division of chemistry to conduct research in the area of theoretical chemistry. He and his research group develop new computational methods that take advantage of advances in high-performance computers. They use these new methods to study important and interesting properties of complex molecular systems at the atomic level, for example large molecular clusters. Currently they are applying these new approaches to learn about the structure, dynamics, and spectroscopy of water clusters, ion-water clusters, and hydrogen clusters . The computer programs resulting from this project are made available free of charge to the scientific community.Professor Mandelshtam's research in Quantum Dynamics is concerned with the development of a novel approach under the general title "Quasirandom Distributed Gaussian Basis" (QDGB) and its applications to computations of vibrational spectra of molecules and clusters. QDGB combines the relatively old idea of using a Gaussian basis with the new ways of distributing this basis by using a quasirandom sequence that samples a particular distribution function optimized for the system in question. Another important aspect of the approach involves the new ways of computing the required multidimensional integrals involving the potential energy matrix elements using quasi-Monte Carlo (QMC). QMC is also based on quasirandom sequences. Unlike the standard MC it has superior convergence properties. QDGB is then used to study vibrational spectra of polyatomic molecules and clusters. In addition, Mandelshtam's research in Statistical Mechanics is concerned with applications of the Diffusion Monte Carlo (DMC) method to study energetics, structure, and nuclear quantum and isotope effects in molecular clusters.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.