Reduced Scaling Real-Time Coupled Cluster Theory

Abstract

Real-time coupled cluster (CC) methods have several advantages over their frequency-domain counterparts, namely, response and equation of motion CC theories. Broadband spectra, strong fields, and pulse manipulation allow for the simulation of complex spectroscopies that are unreachable using frequency-domain approaches. Due to the high-order polynomial scaling, the required numerical time propagation of the CC residual expressions is a computationally demanding process. This scaling may be reduced by local correlation schemes, which aim to reduce the size of the (virtual) orbital space by truncation according to user-defined parameters. We present the first application of local correlation to real-time CC. As in previous studies of locally correlated frequency-domain CC, traditional local correlation schemes are of limited utility for field-dependent properties; however, a perturbation-aware scheme proves promising. A detailed analysis of the amplitude dynamics suggests that the main challenge is a strong time dependence of the wave function sparsity.

Modeling Intermolecular Coulombic Decay with Non-Hermitian Real-Time Time-Dependent Density Functional Theory

“…In general, the majority of theoretical investigation of such processes has relied on static electronic structure calculations involving analysis of the ionization spectrum, − density of states, or broadening of the electronic states through non-Hermitian techniques. − However, with the advent of attosecond spectroscopy, it is now possible to have experimentally time-resolved observation of ultrafast processes with subfemtosecond resolution. − Therefore, there is a benefit to developing practical simulation methods that go beyond static techniques and can more directly report on such experiments. Real-time electronic structure methods, which directly solve for the time propagation of the electronic wave function, provide a powerful class of techniques for accomplishing such a goal. − In the context of electronic relaxation dynamics, a few highly accurate real-time studies of the explicit electronic motion have been performed on small systems, such as using the wave packet propagation method to simulate ICD in the Ne–Ar system and the MCTDH method for Fermions to simulate ICD in model potentials of quantum dots. − Additionally, a few studies have used real-time time-dependent density functional theory (RT-TDDFT) with various levels of success. , …”