Efficient Calculation of the Perturbational Triples Contributions in Coupled Cluster Theory

摘要

Triple substitutions are essential to achieve near-quantitative accuracy in Coupled Cluster (CC) theory. The full inclusion of triples is very demanding computationally, and requires the storage of the O(N6) triples amplitudes, and is thus restricted to small benchmark calculations. Including the triple substitution perturbationally avoids the storage problem and reduces the computational effort. Several such methods have been suggested ([1]; see [2] for review) but the most widely used scheme is CCSD(T) [3].