Reduced-Scaling Coupled Cluster Theory in the Frequency and Time Domains

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With support from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry, Professor Daniel Crawford of Virginia Polytechnic Institute and State University will develop methods and approaches that enable the computational characterization of molecules, especially chiral molecules. A chiral molecule displays handedness; thus, there are left-handed and right-handed forms of the molecule and these forms rotate plane-polarized light waves in opposite 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 even toxic. The accurate prediction of the optical properties of chiral molecules 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 are working to develop robust and accurate computational techniques that are less time-intensive than current methods. These computational tools have to potential to help researchers better understand the relationship between chiral molecular structures and their interactions with light. Further, this research program will the provide for the education and training of graduate and undergraduate students in the fundamental theory and development of quantum chemical methods. Software developed during this project will be 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.Under this award, Professor Daniel Crawford and coworkers at Virginia Tech will endeavor to advance the high-accuracy modeling of chiroptical properties by streamlining coupled cluster theory through complementary approaches. The Crawford group will be 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) to take advantage of their newly developed methods for reducing the dimensionality of the underlying correlated wave functions. In addition, 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, the Crawford team will develop a locally correlated real-time coupled cluster approach that is designed to take advantage of existing linear-scaling frameworks. Finally, they will develop and implement the first simulations of vibrational circular dichroism spectroscopy using advanced correlated wavefunctions. Development of these new models will involve close collaborations with both experimentalists and theorists, a hallmark of studies in the Crawford laboratory.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.