title: Accurate benchmark calculations on the gas-phase basicities of small molecules.
abstract: Accurate benchmark calculations of gas-phase basicities of small molecules are presented and compared with available experimental results. The optimized geometries and thermochemical analyses were obtained from MP2/aug-cc-pVTZ calculations. Two different ab initio electron-correlated methods MP2 and CCSD(T) were employed for subsequent gas-phase basicity calculations, and the single-point energies were extrapolated to the complete basis set (CBS) limit. The overall accuracy for different ab initio methods is compared, and the accuracy in descending order is CCSD(T)_CBS > CCSD(T)/aug-cc-pVDZ > (MP2/aug-cc-pVQZ approximately MP2_CBS) > HF/aug-cc-pVQZ. The best root-mean-squared-error obtained was 1.0 kcal mol(-1) at the CCSD(T)_CBS//MP2/aug-cc-pVTZ level for a test set of 41 molecules. Clearly, accurate calculations for the electron correlation energy are important for the theoretical prediction of molecular gas-phase basicities. However, conformational effects were also found to be relevant in several instances when more complicated molecules were examined.
authors.affiliation: Department of Chemistry and the Quantum Theory Project, 2328 New Physics Building, P.O. Box 118435, University of Florida, Gainesville, Florida 32611-8435, USA.
authors.forename: Xiao
authors.initials: X
authors.lastname: He
authors.forename: Laszlo
authors.initials: L
authors.lastname: Fusti-Molnar
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Merz
mesh_terms: D005030:Ethylenes / Q000737:chemistry; D005740:Gases / Q000737:chemistry*; D006856:Hydrogen Cyanide / Q000737:chemistry; D006862:Hydrogen Sulfide / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D054852:Small Molecule Libraries / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D005030:Ethylenes; D005740:Gases; D054852:Small Molecule Libraries; D014867:Water; D006856:Hydrogen Cyanide; D006862:Hydrogen Sulfide
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