title: Quantum mechanics/molecular mechanics methods can be more accurate than full quantum mechanics in systems involving dispersion correlations.
abstract: The performance of ONIOM(DFT:MM) methods on the structural description of molecules where intramolecular non-covalent interactions play a critical role is examined systematically and compared with that of full DFT methods, both with and without explicit dispersion corrections. The more detailed study is carried out on dithienobicyclo-[4.4.1]-undeca-3,8-diene-11-one ethylene glycol ketal molecule (CSD entry:RESVAN). Accurate description of the non-covalent interactions between two thiophene rings, measured by the optimal S-S distance (X-ray structure 4.29 Å and estimated experimental gas-phase value 4.19 Å), is accomplished by ONIOM(B3LYP:OPLS_2001) [r(S-S) ≈ 4.20 Å] and ONIOM(B3LYP:MMFFs) [r(S-S) ≈ 4.30 Å] calculations, providing results of similar quality to those of dispersion energy corrected density functionals such as B97D [r(S-S)=4.25 Å], B3LYP-D [r(S-S)=4.25 Å], and TPSS-D [r(S-S)=4.22 Å], and much more accurate than those of more conventional density functionals such as B3LYP [r(S-S)=4.65 Å]. The trends were confirmed by calculations on three other molecules with ONIOM(B3LYP:UFF) and full DFT methods.
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ), Av., Països Catalans 16, 43007 Tarragona, Catalonia, Spain.
authors.forename: W M C
authors.initials: WM
authors.lastname: Sameera
authors.forename: Feliu
authors.initials: F
authors.lastname: Maseras
mesh_terms: D018360:Crystallography, X-Ray; D005030:Ethylenes / Q000737:chemistry; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory
chemical_list: D005030:Ethylenes; C036216:ethylene