Accelerating convergence of equation-of-motion coupled-cluster computations using the semi-stochastic CC(P;Q) formalism

Abstract

The recently proposed approach to excited electronic states, in which the deterministic equation-of-motion coupled-cluster (EOMCC) framework is merged with stochastic configuration interaction Quantum Monte Carlo (CIQMC) computations [J.E. Deustua et al., J. Chem. Phys. 150, 111101 (2019)], is combined with the noniterative energy corrections derived from the CC(P;Q) formalism. By examining vertical excitations in CH+ at the equilibrium and stretched geometries and adiabatic excitations in CH and CNC, we demonstrate that the resulting semi-stochastic CC(P;Q) methodology converges target high-level energetics, represented in this study by the EOMCC method with singles, doubles, and triples, in the early stages of CIQMC propagations.