Guandalini Alberto, Cocchi Caterina, Pittalis Stefano, Ruini Alice, Rozzi Carlo Andrea
CNR - Istituto Nanoscienze, Via Campi 213A, I-41125 Modena, Italy.
Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, Via Campi 213A, I-41125 Modena, Italy.
Phys Chem Chem Phys. 2021 Apr 28;23(16):10059-10069. doi: 10.1039/d0cp04958a.
Applications of low-cost non-perturbative approaches in real time, such as time-dependent density functional theory, for the study of nonlinear optical properties of large and complex systems are gaining increasing popularity. However, their assessment still requires the analysis and understanding of elementary dynamical processes in simple model systems. Motivated by the aim of simulating optical nonlinearities in molecules, here exemplified by the case of the quaterthiophene oligomer, we investigate light absorption in many-electron interacting systems beyond the linear regime by using a single broadband impulse of an electric field; i.e. an electrical impulse in the instantaneous limit. We determine non-pertubatively the absorption cross section from the Fourier transform of the time-dependent induced dipole moment, which can be obtained from the time evolution of the wavefunction. We discuss the dependence of the resulting cross section on the magnitude of the impulse and we highlight the advantages of this method in comparison with perturbation theory by working on a one-dimensional model system for which numerically exact solutions are accessible. Thus, we demonstrate that the considered non-pertubative approach provides us with an effective tool for investigating fluence-dependent nonlinear optical excitations.
低成本非微扰方法在实时研究中的应用，如含时密度泛函理论，用于研究大型复杂系统的非线性光学性质正变得越来越流行。然而，对它们的评估仍需要对简单模型系统中的基本动力学过程进行分析和理解。受模拟分子光学非线性这一目标的驱动，这里以四噻吩低聚物为例，我们通过使用单个宽带电场脉冲，即瞬时极限下的电脉冲，研究多电子相互作用系统中超出线性范围的光吸收。我们从含时感应偶极矩的傅里叶变换非微扰地确定吸收截面，该偶极矩可从波函数的时间演化中获得。我们讨论了所得截面与脉冲幅度的依赖性，并通过在一个可获得数值精确解的一维模型系统上工作，突出了该方法与微扰理论相比的优势。因此，我们证明所考虑的非微扰方法为研究与能量密度相关的非线性光学激发提供了一个有效工具。
