Excited-State Absorption by Linear Response Time-Dependent Density Functional Theory

Investigations of the ground and excited states absorption are very important for the development of advanced optical limiters. Linear response time-dependent density-functional theory (LR-TDDFT) has become popular for calculating absorption spectra of molecules in their ground state. However, calculation for the excited state turns out to be much more complicated. In the present paper, it is shown that the transition dipole moments between two excited states can be well estimated based on auxiliary excited-state wavefunctions extracted from the LR-TDDFT calculation. For application, the absorption spectra in zinc phthalocyanine (ZnPc), distyrylbenzene (DSB), and 3-methylthiophenes heptamer (3MT heptamer) are investigated in detail along with different density functional models, and results are compared with experimental data and other theoretical methods. The computational cost of the present method is much cheaper than other theoretical methods, such as quadratic response TDDFT.