Addressing the System-Size Dependence of the Local Approximation Error in Coupled-Cluster Calculations

Over
the last two
decades, the local approximation has been successfully
used to extend the range of applicability of the “gold standard”
singles and doubles coupled-cluster method with perturbative triples
CCSD­(T) to systems with hundreds of atoms. The local approximation
error grows in absolute value with the increasing system size, i.e.,
by increasing the number of electron pairs in the system. In this
study, we demonstrate that the recently introduced two-point extrapolation
scheme for approaching the complete pair natural orbital (PNOs) space
limit in domain-based pair natural orbital CCSD­(T) calculations drastically
reduces the dependence of the error on the system size, thus opening
up unprecedented opportunities for the calculation of benchmark quality
relative energies for large systems.