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 HC1 and the active-space CC calculations for the low-lying excited states of the Be ₃ system.