Benchmark calculations with correlated molecular wave functions. VIII. Bond energies and equilibrium geometries of the CH{sub n} and C{sub 2}H{sub n} (n=1{endash}4) series
- Department of Chemistry, Washington State University, and the Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)
Using systematic sequences of correlation consistent basis sets, the accuracy of calculated bond energies D{sub e}(CH) and equilibrium geometries (r{sub e}, {theta}{sub e}) has been investigated for the CH{sub n} and C{sub 2}H{sub n} series (n=1{endash}4). Perturbation theory (MP2, MP3, MP4), coupled cluster [CCSD, CCSD(T)], and single and multireference configuration interaction (HF+1+2, CAS+1+2) methods have been investigated. Except for the vinyl radical, all of the calculated bond energies showed significant basis set dependence with average errors (standard deviations) of 5.6 ({plus_minus}3.0) kcal/mol for the cc-pVDZ set, 1.4 ({plus_minus}0.8) kcal/mol for the cc-pVTZ set, and 0.5 ({plus_minus}0.4) kcal/mol for the cc-pVQZ set with CCSD(T) wave functions. For the vinyl radical the total variation with basis set was just 0.6 kcal/mol. Strong basis set dependence was also observed for the equilibrium geometries, e.g., for r{sub e}(CH) the average error decreased from 0.020 {Angstrom} (cc-pVDZ) to 0.003 {Angstrom} (cc-pVTZ) to 0.002 {Angstrom} (cc-pVQZ). The effect of including the core electrons in the correlated calculations was also investigated for the two series. Inclusion of core correlation in the CH{sub n} series increased D{sub e}(CH) by 0.13 (CH) to 0.61 kcal/mol (CH{sub 2}) and decreased the equilibrium CH bond lengths by approximately 0.0015 {Angstrom}. For the C{sub 2}H{sub n} series, correlation of the core electrons increased D{sub e}(CH) by 0.18 (C{sub 2}H{sub 4}) to 1.01 (C{sub 2}H) kcal/mol, but decreased D{sub e}(CH) in C{sub 2}H{sub 2} by 0.25 kcal/mol. Predictions are also made for the equilibrium geometries of C{sub 2}H, H{sub 2}CC, and C{sub 2}H{sub 3}, as well as the CH bond strength of vinylidene and the acetylene{endash}vinylidene isomerization energy. {copyright} {ital 1997 American Institute of Physics.}
- DOE Contract Number:
- FG06-89ER75522
- OSTI ID:
- 497641
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 10 Vol. 106; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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