Advanced Quantum Mechanical Methods for the Chiroptical Properties of Molecules in Solution

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T. Daniel Crawford of Virginia Tech University is supported by an award from the Chemical Theory; Models and Computational Methods program in the Chemistry Division to develop theoretical and computational methods for the accurate prediction of the optical properties of chiral molecules in solution remains a challenging task for computational chemistry. A chiral molecule is one in which there are two different versions that are identical in composition but which cannot be superimposed, much like human hands. The "left-handed" and "right-handed" molecules are mirror images of one another. Such molecules are optically active, they can rotate plane-polarized light either clockwise or counter-clockwise. Chiral molecules play an important role in many branches of chemistry, including the chemistry that governs the functioning of living beings. Crawford and his research group focus on the development of robust and efficient methods for computing the special "chiroptical" properties of these molecules, with the overarching goal of providing practical and reliable tools for assigning absolute stereochemical configurations of chiral compounds. These studies are invaluable in the elucidating the intimate relationship between molecular structure and chiroptical response and thus may provide the chemical community with a deeper understanding of the nature of optical activity. The best approach for modeling the intimidating complexity of solvent effects on molecular properties remains elusive, especially for chiroptical properties such as optical rotation (OR), circular dichroism (CD), vibrational Raman optical activity (ROA), and circularly polarized luminescence (CPL), which exhibit an exquisite sensitivity to environmental effects. This project focuses on the development of robust and efficient tools for the high accuracy modeling of chiroptical properties in the liquid phase, including implicit, explicit, and hybrid approaches. Implicit models will be developed to approximate the bulk solute-solvent interaction using both shape- and density- based cavities coupled with potentials derived self-consistently. Explicit solvation effects will be accounted for using a new hybrid QM/MM scheme, including a novel wave-function-embedded periodic approach. Efficient implementation of these models will rely heavily on emerging reduced-scaling methods, particularly within the coupled cluster linear-response approach for non-resonant optical activity.