Reduced-Scaling Quantum Mechanical Response Theory for the Spectroscopic Properties of Molecules in Solution

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Professor T. Daniel Crawford, of Virginia Polytechnic Institute and State University is supported by an award from the Chemical Theory, Models and Computational Methods program to develop computational tools to predict the optical properties of chiral molecules in solution. A chiral molecule has the same atoms connected in a different order. Chiral molecules cannot be super-imposed on their mirror image. There is a "left-handed" and a "right-handed" form each of which turns the waves of light into different directions. Understanding chiral molecules is especially important to the pharmaceutical industry as one chiral form may be of great medicinal value, while the other form may be of no value or toxic. The accurate prediction of the optical properties of chiral molecules dissolved in liquids is a daunting task for computational chemistry. While computer models of simple molecular properties are well established, interactions of chiral molecules with light present unique challenges even for state-of-the-art computational methods. In this research project, Professor Crawford and coworkers develop robust and accurate computational techniques that take less time than current methods. These computational tools allow researchers to understand the relationship between chiral molecular structures and their interactions with light. The new tools provides the chemistry community with a deeper understanding how molecules interact with light. This research program benefits the larger field of computational science through the education and training of graduate and undergraduate students in the fundamental theory and development of quantum chemical methods. Software developed during this project is included in PSI4, a widely used computational chemistry package that is freely available to the community. Dr. Crawford is one of the lead developers of PSI4. Daniel Crawford and coworkers advance the high-accuracy modeling of chiroptical properties in the liquid phase by streamlining coupled cluster theory through complementary approaches. They build upon reduced-scaling methods to develop production-level implementation of an "extended local-pair-natural-orbital" approach, in which the correlation domain for each pair of localized occupied orbitals is constructed based on natural orbitals computed via an approximate second-order field-perturbed density. The Crawford group is extending their recent collaborative work on the development of a "diagrammatic" stochastic coupled cluster approach that exhibits a hundred-fold reduction in the memory costs for the solution of high-accuracy coupled cluster methods (through quadruple excitations). Following their demonstration that the introduction of a time-dependent external electric field yields substantially greater wave function sparsity than that of the field-perturbed wave function, they are developing a locally correlated real-time coupled cluster approach that can take advantage of existing linear-scaling frameworks. Development of these new models involves numerous, well-established collaborations with both experimentalists and theorists. 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.