Calculation of linear and nonlinear optical properties of azobenzene derivatives with Kohn–Sham and coupled-cluster methods

Abstract

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 new tuned range-separated density functional for the accurate calculation of second hyperpolarizabilities

“…25,43 A possible approach to improve the accuracy of the NLOP obtained with the RSH functionals is tuning the parameters that determine their shortrange and long-range regions in the calculation of the exchange energy. Unfortunately, the most popular tuned RSH functionals, which are based on the minimization of J 2 , do not improve the Please do not adjust margins Please do not adjust margins 21,26,38 The main goal of this work is to propose a new type of tuned RSH replacing the minimization of J 2 by an alternative function that provides more accurate second hyperpolarizabilities.…”

“…36,37 Unfortunately, this tuning scheme is, in general, not accurate enough to provide reliable results for γ calculations, giving sometimes even worse results than their corresponding nonoptimized RSH functional. 21,38 Indeed, for cases like conjugated organic oligomers and polymers, which have raised a lot of interest in the field of nonlinear optics due to their very high NLOPs, the usual OT-RSH even decreases the accuracy for γ's. 19,21 Therefore, a novel and more specific strategy is required to compute accurate second hyperpolarizabilities at a moderate computational cost.…”

Polymorphism Dependent 9-Phosphoanthracene Derivative Exhibiting Thermally Activated Delayed Fluorescence: A Computational Investigation

“…It has been variously examined that due to larger Kohn–Sham (KS) delocalization error (DE) or wrong asymptotic behavior in conventional density functionals, sometimes they provide underestimated transition energies, specifically the charge-transfer (CT) states. − For organic molecules, range-separated (RS) or long-range corrected (LC) density functionals are more appropriate in this context, such as Coulomb annulated method (CAM)-B3LYP functional. , For such functionals, the exchange term splits into short-range (DFT) and long-range (HF) domains. The three-parameters error-function RS equation is where r 12 is the interelectronic distance and γ is the range-separation parameter.…”

Accurate Prediction of the S1 Excitation Energy in Solvated Azobenzene Derivatives via Embedded Orbital-Tuned Bethe-Salpeter Calculations

“…We compare the S1 and S2 excitation energies and oscillator strengths of cis and trans AB computed with this approach with recent coupled cluster calculations 27 performed with aug-cc-pVTZ basis set, and find an excellent agreement with our BSE/GWg/DFTg results. The comparison of the excitation energies is reported in Table S5, together with results from previous CASPT2 50 and recent TDDFT 13 the electronic gap of cis and trans AB (see Fig. S5): the electron removal energies decrease as shown in Fig.…”