A linear-scaling method for non-covalent interactions

A novel method for the accurate and efficient calculation of interaction energies in weakly-bound complexes comprised of a large number of molecules is presented. The new ALMO+RPAd method circumvents the prohibitive scaling of coupled cluster singles and doubles while still providing similar accuracy across a diverse range of intermolecular interactions. Tests on various dimers and the S66 benchmark set demonstrate results within 0.5 kcal/mol of coupled cluster singles and doubles results. On a large cluster of water molecules, we achieve calculations involving over 3500 orbital and 12000 auxiliary basis functions in under ten minutes on a single CPU core.