Quantum chemical estimation of effective local dielectric constants in crystal surroundings

COMP 282

Wibke Sudholt, Department of Chemistry and Biochemistry and San Diego Supercomputer Center, University of California, San Diego, 9500 Gilman Drive, Mail Code 0505, La Jolla, CA 92093-0505, Kim K. Baldridge, Integrative Computational Sciences, San Diego Supercomputer Center, 9500 Gilman Drive, Mail Code 0505, La Jolla, CA 92093-0505, and J. Andrew McCammon, Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Mail Code 0365, La Jolla, CA 92093-0365.
The polarity and polarizability of the environment often has huge influence on the physics, chemistry and biology of molecules in condensed media. Dielectric continuum models are an important concept to describe such effects on a mean-field basis. Apart from providing a quantitative scale for the experimentalist, they also allow relatively cheap theoretical calculations. However, while dielectric constants are easily available for common solvents, they are often unknown for more complex materials. In addition, the measured values are essentially macroscopic and may not adequately represent the microscopic influence of the surroundings. In this contribution, we introduce a general procedure to estimate an effective dielectric constant which models the local effects of the environment on a molecule. It makes use of the experimental crystal structure and of gradients calculated by quantum chemical reaction-field theory. Applications cover organic compounds, host-guest and protein-ligand complexes. Known limitations and possible extensions of the method are discussed.