Explicitly correlated local coupled‐cluster methods using pair natural orbitals

Recently developed explicitly correlated local coupled‐cluster methods [PNO‐LCCSD(T)‐F12] are reviewed. Extensive benchmarks for reaction energies and intermolecular interaction energies are presented, in which the convergence of the results with respect to all local approximations is studied. The explicit correlation treatment (F12) is shown to be essential to minimize basis set incompleteness errors, as well as errors caused by domain approximations. Generally, the errors of relative energies due to local approximations can be reduced to below 1 kcal/mol. The methods are well parallelized, and using small computer clusters with 100–200 computing cores, calculations for systems with 100–200 atoms using augmented triple‐ζ basis sets can be carried out within a few hours of elapsed time. Recommendations are made on how such calculations should be carried out, how the accuracy can be tested, and which computational resources are required.