Charles David Sherrill of the New York University is receiving an award from the Theory, Models and Computational Methods program of the Chemistry Division to carry out research, development, and application of theoretical models for potential energy landscapes of challenging chemical systems. The computational machinery is developed and used to study pi-pi interactions in several large molecular aggregates. These interactions are critical in biomolecular structure, drug docking, and supramolecular chemistry. The focus of the endeavor is on innovations of the software implementation of symmetry-adapted perturbation theory (SAPT) and exchange-dipole moment (XDM) variants of DFT. New approaches in this project provide the chemical, molecular biology, and soft materials communities with very efficient software implementations of sophisticated algorithms. These innovations are fundamental to test newly synthesized complexes in experimental groups at Georgia Tech.
Understanding the fundamentals of pi-pi interactions and how they can be tuned by substituents is directly relevant to researchers studying molecular recognition and supramolecular chemistry. Theoretical methods and the majority of the code developed through this work is to be released in the freely available, open-source PSI package. New chemical and theoretical understanding developed through this project is incorporated into Sherrill's Web notes on quantum chemistry and into workshops taught by him with the goal to train the next generation of students who know not just how to use code, but also know how to develop new models, simulation and the underlying software. This project contributes to the continued training of graduate and undergraduate students in quantum chemistry methods development.
Our project focused on the development of theoretical methods and computer algorithms for performing simulations on molecules using quantum mechanics. In particular, we are very interested in how two molecules attract or repel each other. This is an important question that influences the properties of liquids, the structure of crystals, and how drugs bind to their targets in the body. A better understanding of interactions between molecules could ultimately assist efforts in developing designed materials and in rational drug design. We developed user-friendly, very fast software (perhaps the world's fastest) to compute the strength of interactions between molecules using a technique called symmetry-adapted perturbation theory (SAPT). This software has been made publicly and freely-available as open-source software at our website (www.psicode.org) as part of the Psi4 program. We also developed very fast software to perform high-quality, benchmark-level computations of molecules using the "gold standard" of quantum chemistry, a method called coupled-cluster through perturbative triples, CCSD(T). This software is also available as part of our open-source Psi4 program. Using the software developed as part of this grant, in addition to existing software, we explored numerous challenging problems in chemistry, from buckybowls to DNA and RNA. We found that the details of how electron clouds interact when two molecules come near each other (technically, "charge penetration") can be very important effect in chemistry, even though it is not explicitly considered by many chemists. Future work should explore new ways to include these charge penetration effects in moecular simulations. They are especially important in DNA, RNA, and organic materials that feature stacking of "aromatic" groups. In addition to exploring these and other scientific questions, and providing free software to other scientists for use in their investigations, and we developed tools to make the software easy to use by students. Thousands of Georgia Tech undergraduates have used our software in laboratory exercises using a web-based interface. We have begun promoting the educational uses of this software to other campuses. The research conducted under this project provided an opportunity to train postdoctoral researchers, graduate students, undergraduate students, and even a high-school student who assisted with the work.
