Approximate Exponential Integrators for Time-Dependent Equation-of-Motion Coupled Cluster Theory

With growing demand for time-domain simulations of correlated many-body systems, the development of efficient and stable integration schemes for the time-dependent Schr\"odinger equation is of keen interest in modern electronic structure theory. In the present work, we present two novel approaches for the formation of the quantum propagator for time-dependent equation-of-motion coupled cluster theory (TD-EOM-CC) based on the Chebyshev and Arnoldi expansions of the complex, non-hermitian matrix exponential, respectively. This builds upon earlier by Cooper, et al. [J. Phys. Chem. A, 2021 125, 5438-5447] which presented a similar TD-EOM-CC integration scheme based on the short-iterative Lanczos (SIL) method. The proposed algorithms are compared with SIL, the fourth-order Runge-Kutta method (RK4), and exact dynamics for a set of small test problems. For each of cases studied, both of the proposed integration schemes demonstrate superior accuracy and efficiency than the reference simulations.
Comment: 23 pages, 3 figures