Optical spectra from molecules to crystals: Insight from many-body perturbation theory

摘要: Time-dependent density-functional theory (TDDFT) often successfully reproduces excitation energies of finite systems, already in the adiabatic local-density approximation (ALDA). Here we show for prototypical molecular materials, i.e., oligothiophenes, that ALDA largely fails and explain why this is so. By comparing TDDFT with an in-depth analysis based on many-body perturbation theory, demonstrate correlation effects crucially impact character optical excitations not only molecules increasing length crystalline environment, but even isolated small molecules. We argue high-level methodologies, which explicitly include effects, can reproduce spectra materials equal accuracy from gas phase to crystal structures.