Reduced Scaling Real-Time Coupled Cluster Theory

TL;DR

This paper introduces the first application of local correlation schemes to real-time coupled cluster methods, aiming to reduce computational scaling while addressing challenges posed by wave function sparsity dynamics.

Contribution

It presents a novel perturbation-aware local correlation scheme for real-time CC, improving computational efficiency for complex spectroscopic simulations.

Findings

Local correlation reduces computational cost.

Perturbation-aware scheme improves accuracy.

Wave function sparsity varies strongly over time.

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 which 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 truncating it 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 the main challenge is a strong time-dependence of the wave function sparsity.