A DLPNO‐CCSD(T) benchmarking study of intermolecular interactions of ionic liquids

Abstract

The accuracy of correlation energy recovered by coupled cluster single-, double-, and perturbative triple-excitations, CCSD(T), has led to the method being considered the gold standard of computational chemistry. The application of CCSD(T) has been limited to medium-sized molecular systems due to its steep scaling with molecular size.The recent development of alternative domain-based local pair natural orbital coupled-cluster method, DLPNO-CCSD(T), has significantly broadened the range of chemical systems to which CCSD(T) level calculations can be applied. Condensed systems such as ionic liquids (ILs) have a large contribution from London dispersion forces of up to 150 kJ mol À1 in large-scale clusters. Ionic liquids show appreciable charge transfer effects that result in the increased valence orbital delocalization over the entire ionic network, raising the question whether the application of methods based on localized orbitals is reliable for these semi-Coulombic materials. Here the performance of DLPNO-CCSD(T) is validated for the prediction of correlation interaction energies of two data sets incorporating single-ion pairs of protic and aprotic ILs. DLPNO-CCSD(T) produced results within chemical accuracy with tight parameter settings and a non-iterative treatment of triple excitations. To achieve spectroscopic accuracy of 1 kJ mol À1 , especially for hydrogen-bonded ILs and those containing halides, the DLPNO settings had to be increased by two orders of magnitude and include the iterative treatment of triple excitations, resulting in a 2.5-fold increase in computational cost. Two new sets of parameters are put forward to produce the performance of DLPNO-CCSD(T) within chemical and spectroscopic accuracy.

Molecular Understanding and Practical In Silico Catalyst Design in Computational Organocatalysis and Phase Transfer Catalysis—Challenges and Opportunities

“…For DLPNO-CCSD(T), its accuracy is dictated by three main cutoffs to determine the molecular orbital space that will be included. For the recommendation of cutoff choice and its impact, the reader is referred to the work of Neese and co-workers [ 69 ] and Seeger and Izgorodina (on ionic liquids) [ 70 ]. In their ionic S N 2 computational study, Ho and co-workers presented a comparison of canonical and DLPNO CCSD(T) with various basis set sizes [ 54 ].…”

Unravelling ionic liquid solvent effects for a non-polar Cope rearrangement reaction

“…[43][44][45] Recently IL interactions have been benchmarked for the domain-based local pair natural orbital coupled-cluster method DLPNO-CCSD(T) with noted recovery of dispersion and correlation and are known to reach 1 kJ mol À1 accuracy. 46 DLNPO-CCSD(T) calculations were carried out with cc-pVTZ basis sets, with convergence on the energy to 10 À8 a.u. and on the RMS density 5.0 Â 10 À9 (tightSCF).…”

On the existence of CO32− microsolvated clusters: a theoretical study

“…The DLPNO-CCSD(T) approach was previously shown to be excellent in application to ''loosely''bonded systems. [46][47][48][49][50] All DLPNO-CCSD(T)-F12 calculations were performed using Quasi-Restricted Orbitals 51 (QROs) obtained from the UHF reference wavefunction to eliminate the influence of possible spin-contamination. The F12 ansatz was realized with the resolution-of-identity approximation (F12/D); the corresponding auxiliary basis sets were cc-pVTZ-F12-CABS and cc-pVQZ-F12-MP2fit.…”