Automated derivation and parallel computer implementation of renormalized and active‐space coupled‐cluster methods

Our recent efforts that have led to an automated derivation and computer implementation of the renormalized and active‐space coupled‐cluster (CC) methods with Tensor Contraction Engine (TCE) are summarized. The TCE‐generated renormalized and active‐space CC computer codes are parallel and applicable to closed‐ and open‐shell references, enabling accurate calculations of potential energy surfaces along bond‐breaking coordinates and excited states displaying a significant multi‐reference character. The effectiveness of the new codes in describing electronic quasi‐degeneracies is illustrated by the renormalized CC calculations of the potential energy curve of HCl and the active‐space CC calculations for the low‐lying excited states of the Be3 system.