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This paper introduces a coupled-cluster formalism for imaginary-time evolution, enabling exploration of coupled-cluster solutions beyond standard amplitude equations. The method leverages the evolution trajectory to extract additional information when standard solutions are ill-defined. By minimizing the coupled-cluster energy variance, the approach identifies physically regularized amplitudes, offering a robust alternative when traditional methods fail.
Unreasonable coupled-cluster solutions? This new imaginary-time evolution formalism and energy variance minimization might just save the day.
We discuss a coupled-cluster formalism for carrying out imaginary-time evolution from an arbitrary reference, and study the properties of the resulting evolution trajectories. The evolution converges to a solution of the standard coupled-cluster amplitude equations in the long-time limit if a finite valued limit exists, but when such a limit does not exist, the trajectories still contain additional information beyond the standard solutions. We introduce the coupled-cluster energy variance which through its minima identifies physically regularized coupled-cluster amplitudes when the solutions of the amplitude equations are unreasonable. We demonstrate the value of this formalism in several exploratory examples within single- and multi-reference coupled-cluster formulations.
