New accurate benchmark energies for large water clusters: DFT is better than expected

Abstract

In this work, we use MP2 and coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] as well as their corresponding explicitly correlated (F12) counterparts to compute the interaction energies of water icosamers. The incremental scheme is used to compute benchmark energies at the CCSD(T)/CBS(45) and CCSD(T)(F12*)/cc-pVQZ-F12 level of theory. The four structures, dodecahedron, edge sharing, face sharing, and fused cubes, are part of the WATER27 test set and therefore, highly accurate interaction energies are required. All methods applied in this work lead to new benchmark energies for these four systems. To obtain these values, we carefully analyze the convergence of the interaction energies with respect to the basis set. Furthermore, we investigate the influence of the basis set superposition error and the core-valence correlation. The interaction energies are: dodecahedron -198.6 kcal/mol, edge sharing -209.7 kcal/mol, face sharing -208.0 kcal/mol, and fused cubes -208.0 kcal/mol. For water clusters, we recommend to use the PW6B95 density functional of Truhlar in combination with Grimme's dispersion correction (D3), as the mean absolute error is 0.9 and the root mean-squared deviation is only 1.4 kcal/mol.

Small Atomic Orbital Basis Set First‐Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources

“…Even with large basis set dispersion‐corrected DFT calculations, it is difficult to reach this accuracy. This can partially be attributed to the basis set (6‐31+G(2d,2p)) which contains two sets of additional polarization functions, as well as a diffuse set of sp ‐functions on nonhydrogen atoms, which is known to be important for these systems . Therefore, the number of basis functions per atom is more comparable to a TZ basis and much larger than in def2‐SV(P).…”

“…This can partially be attributed to the basis set (6-31 + G(2d,2p)) which contains two sets of additional polarization functions, as well as ad iffuse set of sp-functions on nonhydrogen atoms, which is known to be important for theses ystems. [5,86,87] Therefore, the number of basis functions per atom is more comparable to aT Zb asis and much larger than in def2-SV(P). The B3LYP-DCP results for S22 and S66 8 are also very good and the MARDs of 7.7a nd 0.5 %, respectively,a re the lowest ones reported here.…”

“…[58] For the (H 2 O) 20 complex contained in the WATER27 set we use the reference values computed on the incremental CCSD(T)(F12*) j MP2-F12 + DMP2 level by Friedrich. [87] The L7 test set comprises seven larger,m ostly dispersion-stabilized complexes of organic molecules.W eu se the revised referencev alues on the estimated DLPNO-CCSD(T)/CBS*l evel of theory. [90] The S30L set is an extension of the S12L set, [59,60] which was the first test set for large host-guest complexes.…”

Benchmarking Quantum Chemical Methods: Are We Heading in the Right Direction?

“…Thec urrent most complete set of benchmark sets, the GMTKN30, [21] includes only as mall amount of experimental reference data ( Figure 2). Thea cceptance of CCSD-(T) as a" gold standard" [22] has been ap articular encouragement to the practice,f rom DFT benchmarking [23,24] up to theory-only blind-test challenges. [25] As further evidence,i f one looks again at the GMTKN30 database,14/30 sets use as reference data estimated CCSD(T)/CBS limits.E ven improvements beyond CCSD(T) are sometimes judged without any reference to experiment.…”

Quantenchemische Methoden im Leistungsvergleich: Stimmt die Richtung noch?

“…Die derzeit vollständigste Datenbank fürR eferenzwerte, GMTKN30, [21] enthält nur eine kleine Zahl experimenteller Referenzdaten (Abbildung 2). Die Akzeptanz von CCSD(T) als "Goldstandard" [22] hat diese Praxis vom DFT-Leistungsvergleich [23,24] bis zu reinen Theorie-Blindwettbewerben [25] stark ermutigt. Dies folgt auch aus einer genaueren Analyse der GMTKN30-Datenbank:1 4d er 30 Datensätze beziehen sich auf geschätzte CCSD(T)-Extrapolationen zu einem vollständigen Basissatz.…”