The correlation-consistent composite approach: Application to the G3/99 test set

Abstract

The correlation-consistent composite approach ͑ccCA͒, an ab initio composite technique for computing atomic and molecular energies, recently has been shown to successfully reproduce experimental data for a number of systems. The ccCA is applied to the G3/99 test set, which includes 223 enthalpies of formation, 88 adiabatic ionization potentials, 58 adiabatic electron affinities, and 8 adiabatic proton affinities. Improvements on the original ccCA formalism include replacing the small basis set quadratic configuration interaction computation with a coupled cluster computation, employing a correction for scalar relativistic effects, utilizing the tight-d forms of the second-row correlation-consistent basis sets, and revisiting the basis set chosen for geometry optimization. With two types of complete basis set extrapolation of MP2 energies, ccCA results in an almost zero mean deviation for the G3/99 set ͑with a best value of −0.10 kcal mol −1 ͒, and a 0.96 kcal mol −1 mean absolute deviation, which is equivalent to the accuracy of the G3X model chemistry. There are no optimized or empirical parameters included in the computation of ccCA energies. Except for a few systems to be discussed, ccCA performs as well as or better than Gn methods for most systems containing first-row atoms, while for systems containing second-row atoms, ccCA is an improvement over Gn model chemistries.

Enthalpy of Formation of the Cyclohexadienyl Radical and the C−H Bond Enthalpy of 1,4-Cyclohexadiene: An Experimental and Computational Re-Evaluation

“…To complement the experiments, the ∆ f H 298.15°o f C 6 H 7 was computed with a density functional (B3LYP) method, as well as with the G3B3 model chemistry, 29 the G3B3(MP2)-RAD model chemistry developed by Radom and coauthors, 30 the correlation-consistent composite approach (ccCA) [31][32][33] devel-* To whom correspondence should be addressed. E-mail: akwilson@unt.edu (A.K.W.…”

“…35 All computations using an ROHF reference were carried out using Molpro 2006.1. 36 The ccCA methodology [31][32][33] is as follows. For ccCA, structures were optimized at the B3LYP level of theory with the cc-pVTZ basis sets.…”

“…These two MP2 CBS energies are then averaged. Additive corrections to the MP2 energies to account for higher order electron correlation, core-valence correlation, and treatment of scalar relativistic effects were then made using the standard ccCA formalism in ref 33. For "ROHF-ccCA", the same ccCA approach was used, but with ROHF wave functions.…”

Activation of Carbon−Hydrogen and Hydrogen−Hydrogen Bonds by Copper−Nitrenes: A Comparison of Density Functional Theory with Single- and Multireference Correlation Consistent Composite Approaches

“…[39][40][41][42][43] Hence, the ccCA approach was employed in this study to compare with results obtained from DFT methods. Classical activation barriers as predicted by ccCA 42 were in much better agreement than G3B as compared to very high accuracy computed values obtained from the Truhlar et al databases.…”

Theoretical study of thermochemical properties using composite methods adapted to ONIOM

“…21 There are other theories to predict accurate thermochemical data of chemical compounds. The correlation consistent composite approach (ccCA), [22][23][24] the complete basis set methods (CBS) [25][26][27][28] and the Weizmann theories (Wn), [29][30][31][32] are examples of alternatives to the gaussian-n theories.…”