I will present results that show the ideal basis set (for both accuracy and computational time) and ideal amount of explicit solvent that must be included in the quantum mechanical (QM) portion of a quantum mechanical/molecular mechanical (QM/MM) system to compute converged aqueous UV-Vis absorption spectra. This study determines the QM system size necessary to capture realistic solute-solvent interactions. Results for a series of solutes of varying polarity are presented while changing the basis set and QM region size. Looking at the resulting spectra, we see convergence of λmax is achieved faster for larger basis sets and the required QM region size to achieve convergence is approximately two solvation spheres or about 200 QM water molecules.  We also find that using mixed basis sets can reduce the computation cost by 96% while keeping the excitation energies within 1% error of treating the entire QM system with a larger basis set.

Computing aqueous absorption spectra: The effect of solute polarity and basis set on convergence with respect to the amount of explicit solvent

251st National Meeting (2016)

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