Linear polarizabilities and second hyperpolarizabilities of streptocyanines: Results from broken‐Symmetry DFT and new CCSD(T) benchmarks. Issue 28 (3rd October 2018) - Xu, Lihua
Abstract : We present a detailed analysis of the linear polarizability ( α ) and second hyperpolarizability ( γ ) in a series of streptocyanines, as predicted with various range‐separated functionals and CCSD(T)‐based methods. Contrary to previous work on these systems, we find that the lowest‐energy electronic states for the larger streptocyanine oligomers are not closed‐shell singlets, and improved accuracy can be obtained with certain DFT methods by allowing the system to relax to a lower‐energy broken‐symmetry solution. Our extensive analyses are complemented by new large‐scale CCSD(T) and explicitly correlated CCSD(T)‐F12 calculations that comprise the most complete and accurate benchmarks of α and γ for the streptocyanine systems to date. Taken together, our CCSD(T) and broken‐symmetry DFT calculations (1) show that the MP2 benchmarks used in previous studies still exhibit significant errors (~ 25% for α and ~100% for γ ) and, therefore, the MP2 calculations should not be used as reliable benchmarks for polarizabilities or hyperpolarizabilities, and (2) emphasize the importance of testing for a lower‐energy open‐shell configuration when calculating nonlinear optical properties for these systems. © 2018 Wiley Periodicals, Inc. Abstract : Contrary to previous studies, the electronic states of large streptocyanine oligomers are not closed‐shell singlets, and certain DFT methods become more accurate when the system is allowed to relax to a lower‐energy broken‐symmetry solution.