Lewis Alan M, Berkelbach Timothy C
Department of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637, United States.
Department of Chemistry, Columbia University, New York, New York 10027, United States.
J Phys Chem Lett. 2020 Mar 19;11(6):2241-2246. doi: 10.1021/acs.jpclett.0c00031. Epub 2020 Mar 5.
Linear and nonlinear spectroscopies are powerful tools used to investigate the energetics and dynamics of electronic excited states of both molecules and crystals. While highly accurate calculations of molecular spectra can be performed relatively routinely, extending these calculations to periodic systems is challenging. Here, we present calculations of the linear absorption spectrum and pump-probe two-photon photoemission spectra of the naphthalene crystal using equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD). Molecular acene crystals are of interest due to the low-energy multiexciton singlet states they exhibit, which have been studied extensively as intermediates involved in singlet fission. Our linear absorption spectrum is in good agreement with experiment, predicting a first exciton absorption peak at 4.4 eV, and our two-photon photoemission spectra capture the qualitative behavior of multiexciton states, whose double-excitation character cannot be captured by current methods. The simulated pump-probe spectra provide support for existing interpretations of two-photon photoemission experiments in closely related acene crystals such as tetracene and pentacene.
线性光谱学和非线性光谱学是用于研究分子和晶体电子激发态的能量学和动力学的强大工具。虽然分子光谱的高精度计算相对常规地就能进行，但将这些计算扩展到周期性体系具有挑战性。在此，我们使用含单双激发的运动方程耦合簇理论（EOM-CCSD）给出了萘晶体的线性吸收光谱和泵浦-探测双光子光电子能谱的计算结果。分子并苯晶体因其展现出的低能多激子单重态而备受关注，这些单重态作为单重态裂变所涉及的中间体已得到广泛研究。我们的线性吸收光谱与实验结果吻合良好，预测在4.4 eV处有第一个激子吸收峰，并且我们的双光子光电子能谱捕捉到了多激子态的定性行为，其双激发特性无法被当前方法捕捉。模拟的泵浦-探测光谱为在诸如并四苯和并五苯等密切相关的并苯晶体中双光子光电子能谱实验的现有解释提供了支持。
