Modeling the UV absorption spectrum of the hydroxyl anion in water

In this work, the experimental UV absorption spectrum of water in alkaline conditions has been modeled by capturing the most relevant water molecular clusters, selected by Principal Component Analysis on the structures sampled by classical Molecular Dynamics simulations, and adding the effect of the environment using a QM/MM procedure, the Perturbed Matrix Method. Such an approach allowed the treatment of the relevant molecular clusters with high-level QM methods, while correctly including the effect of the environment, both aspects necessary to accurately reproduce the wavelength of the absorption maximum and the intensity of the experimental spectrum. • The experimental UV absorption spectrum of water in alkaline conditions has been modelled by a theoretical-computational approach. • Relevant solvent clusters have been determined by principal component analysis. • QM/MM calculations on selected clusters accurately reproduce the experimental UV absorption spectrum. • The effect of the solvent molecules outside the clusters is relevant. • Such an approach can be easily extended to treat any small solutes in solutions.