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Calibration study of the CCSD(T)-F12a/b methods for and small hydrocarbons
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FIG. 1.

Convergence of the complete basis set estimates of the total CCSD(T)(FC) energy for the neon atom. The exact value (−128.869 236), represented by the horizontal line, is taken from the work of Barnes et al. (Ref. 58) which was derived from basis sets up through cc-pV10Z (up to n-type functions). Error bars are based on the half the spread among the various estimates. The Schwenke formula was parametrized using Ne as one of seven systems in its training set.

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FIG. 2.

Comparison of standard CCSD(T)/CBS and CCSD(T)-F12x, , atomization energies (kcal/mol) for the first four normal alkanes. The aug-cc-pVnZ basis sets were used in the standard calculations. The cc-pVnZ-F12 basis sets were used in the F12 calculations. The F12b/CBS limit, indicated by a solid horizontal line, was based on the cc-pVTZ-F12/cc-pVQZ-F12 basis set pair.


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Table I.

CBS(exp.) C–H and C–C bond lengths (Å) from standard CCSD(T)(FC) calculations.

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Table II.

Frozen core CCSD(T) and CCSD(T)-F12x total energies, atomization energies and selected internal coordinates. Total energies are expressed in hartrees. Atomization energies are in kcal/mol and internal coordinates are in angstroms and degrees. Bond lengths are converged to approximately . Open-shell systems were treated with the R/U method. The geminal Slater exponent values are 0.9 (cc-pVDZ-F12), 1.0 (cc-pVTZ-F12), and 1.0 (cc-pVQZ-F12). is allene. is the allyl radical. is cyclopropane. is n-propane. is trans-1,3-butadiene. is n-butane. is n-pentane. is n-hexane. NA: not available.

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Table III.

CCSD(T) and CCSD(T)-F12a/b harmonic frequencies . CCSD(T) calculations were performed with the aug-cc-pVnZ basis sets. CCSD(T)-F12a/b calculations were performed with the cc-pVnZ-F12 basis sets.

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Table IV.

CCSD(T) and CCSD(T)-F12b core/valence corrections for and . Units are (kcal/mol), (Å), and .

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Table V.

CCSD(T)-F12b and CCSD(T)/CBS comparison statistics. Units: energy are in Hartrees, atomization energies are in kcal/mol, and bond lengths are in angstroms.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Calibration study of the CCSD(T)-F12a/b methods for C2 and small hydrocarbons