Calculation of linear and nonlinear optical properties of azobenzene derivatives with Kohn-Sham and coupled-cluster methodsElectronic supplementary information (ESI) available: Additional plots related to the tuning procedure, TD-KST results of AB with larger basis sets, solvent dependent α and γ values and corresponding plots. See DOI: 10.1039/c7cp08655e

Linear polarizabilities ( α ) and second hyperpolarizabilities ( γ ) of unsubstituted azobenzenes and 'push-pull' azobenzene derivatives are investigated using Kohn-Sham theory (KST) and coupled-cluster (CC) approaches. Various standard exchange-correlation functionals as well as a non-empirically 'tuned' long-range corrected (LC) functional with range-separated exchange are used in the KST calculations. When compared to correlated ab initio calculations and measurements, the tuned functional gives accurate low-energy excitation energies, especially for charge transfer (CT) transitions, and performs well for α . Basis set and solvent effects are also studied. In contrast to expectations, but in agreement with a prior study of π-conjugated systems that do not have low-energy CT excitations, the improvements of the CT excitation energies for the push-pull π-chromophores due to tuning do not go along with clear improvements of γ toward the CC reference data, likely due to the importance of the dynamic electron correlation for this property. A non-empirically tuned generalized Kohn-Sham functional allows the prediction of accurate low-energy excitation energies and linear polarizabilities. Second hyperpolarizabilities are not improved when compared to coupled-cluster benchmark data.