Understanding excitation from ground state to the singlet excited state through simulating absorption spectra of a molecule is essential to predicting the rate of the photoreaction. Excitation energies and oscillator strengths were calculated using different theories and methods. Among all theories, a new approach was selected to model the photon absorption: Molecular Dynamics–Time Dependent Density Functional Theory (MD-TDDFT). An aniline molecule equilibrates in the presence of a number of water molecules at room temperature using 6-311++G** basis set. Excitation energy and oscillator strength of aniline geometries in equilibrium are then calculated using TDDFT with w-B97X-D, CAMB3LYP, or M06-2X functional. As a theoretical benchmark, OEMCCSD calculation was carried out with optimized geometry from using using 6-311++G** basis set and implicit water model implemented using Polarizable Continuum Model (PCM). The computed physical properties from MD-TDDFT and OEMCCSD were then compared with data from experimental absorption spectra to evaluate the accuracy of the two methods. Absorption spectra’s underlying modified Gaussian functions were decomposed and integrated to calculate experimental oscillator strength at a certain excitation energy using an R code written by Peter Cohen. The more accurate method would be applied to triclosan and other water contaminants to predict the rate of their photodegradations in the environment.

UV-Vis molecular absorption spectra: Benchmarking <i>ab initio </i>computational methods for the quantitative prediction of sunlight-driven pollutant degradation in aquatic environments

251st National Meeting (2016)

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UV-Vis molecular absorption spectra: Benchmarking ab initio computational methods for the quantitative prediction of sunlight-driven pollutant degradation in aquatic environments