title: Toward an Accurate and Inexpensive Estimation of CCSD(T)/CBS Binding Energies of Large Water Clusters.
abstract: Owing to the steep scaling behavior, highly accurate CCSD(T) calculations, the contemporary gold standard of quantum chemistry, are prohibitively difficult for moderate- and large-sized water clusters even with the high-end hardware. The molecular tailoring approach (MTA), a fragmentation-based technique is found to be useful for enabling such high-level ab initio calculations. The present work reports the CCSD(T) level binding energies of many low-lying isomers of large (H2O)n (n = 16, 17, and 25) clusters employing aug-cc-pVDZ and aug-cc-pVTZ basis sets within the MTA framework. Accurate estimation of the CCSD(T) level binding energies [within 0.3 kcal/mol of the respective full calculation (FC) results] is achieved after effecting the grafting procedure, a protocol for minimizing the errors in the MTA-derived energies arising due to the approximate nature of MTA. The CCSD(T) level grafting procedure presented here hinges upon the well-known fact that the MP2 method, which scales as O(N(5)), can be a suitable starting point for approximating to the highly accurate CCSD(T) [that scale as O(N(7))] energies. On account of the requirement of only an MP2-level FC on the entire cluster, the current methodology ultimately leads to a cost-effective solution for the CCSD(T) level accurate binding energies of large-sized water clusters even at the complete basis set limit utilizing off-the-shelf hardware.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.
authors.forename: Nityananda
authors.initials: N
authors.lastname: Sahu
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.
authors.forename: Gurmeet
authors.initials: G
authors.lastname: Singh
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.
authors.forename: Apurba
authors.initials: A
authors.lastname: Nandi
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208 016, India.
authors.forename: Shridhar R
authors.initials: SR
authors.lastname: Gadre