The correlation consistent composite approach (ccCA): An alternative to the Gaussian-n methods
Date: March 17, 2006
Creator: DeYonker, Nathan J.; Cundari, Thomas R., 1964- & Wilson, Angela K.
Description: This article discusses the correlation consistent composite approach (ccCA). Abstract: An alternative to the Gaussian-n (G1, G2, and G3) composite methods of computing molecular energies is proposed and is named the "correlation consistent composite approach" (ccCA, ccCA-CBS-1, ccCA-CBS-2). This approach uses the correlation consistent polarized valence (cc-pVXZ) basis sets. The G2-1 test set of 48 enthalpies of formation (∆Hf), 38 adiabatic ionization potentials (IPs), 25 adiabatic electron affinities (EAs), and 8 adiabatic proton affinities (PAs) are computed using this approach, as well as the ∆Hf values of 30 more systems. Equilibrium molecular geometries and vibrational frequencies are obtained using B3LYP density functional theory. When applying the ccCA-CBS method with the cc-pVXZ series of basis sets augmented with diffuse functions, mean absolute deviations within the G2-1 test set compared to experiment are 1.33 kcal molˉ¹ for ∆Hf, 0.81 kcal molˉ¹ for IPs, 1.02 kcal molˉ¹ for EAs, and 1.51 kcal molˉ¹ for PAs, without including the "high-level correction" (HLC) contained in the original Gn methods. Whereas the HLC originated in the Gaussian-1 method as an isogyric correction, it evolved into a fitted parameter that minimized the error of the composite methods, eliminating its physical meaning. Recomputing the G1 and G3 enthalpies ...
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Computational s-Block Thermochemistry with the Correlation Consistent Composite Approach
Date: October 3, 2007
Creator: DeYonker, Nathan J.; Ho, Dustin S.; Wilson, Angela K. & Cundari, Thomas R., 1964-
Description: This article discusses computational s-block thermochemistry with the correlation consistent composite approach. Abstract: The correlation consistent composite approach (ccCA) is a model chemistry that has been shown to accurately compute gas-phase enthalpies of formation for alkali and alkaline earth metal oxides and hydroxides (Ho, D.S.; DeYonker, N.J.; Wilson, A.K.; Cundari, T.R., J. Phys. Chem. A 2006, 110, 9767). The ccCA results contrast to more widely used model chemistries where calculated enthalpies of formation for such species can be in error by up to 90 kcal molˉ¹. In this study, the authors have applied ccCA to a more general set of 42 s-block molecules and compared the ccCA ∆Hf values to values obtained using the G3 and G3B model chemistries. Included in this training set are water complexes such as Na(H₂O)n⁺ where n = 1 - 4, dimers and trimers of ionic compounds such as (LiCl)₂ and (LiCl)₃, and the largest ccCA computation to date: Be-(acac)₂, BeC₁₀H₁₄O₄. Problems with the G3 model chemistries seem to be isolated to metal-oxygen bonded systems and Be-containing systems, as G3 and G3B still perform quite well with a 2.7 and 2.6 kcal mol⁻¹ mean absolute deviation (MAD), respectively, for gas-phase enthalpies of formation. The MAD ...
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Catalytic Synthesis of Arylisocyanates from Nitroaromatics. A Computational Study
Date: January 10, 2007
Creator: Kazi, Abul B.; Cundari, Thomas R., 1964-; Baba, Eduard; DeYonker, Nathan J.; Dinescu, Adriana & Spaine, Lloyd
Description: This article discusses catalytic synthesis of arylisocyanates from nitroaromatics. Abstract: Several conclusions of interest have emerged from a computational study of copper-catalyzed phenylisocyanate synthesis from nitrobenzene and carbon monoxide. Nitrobenzene complexes coordinate in a κ1-N fashion. With regard to thermodynamics, differences were observed for neutral (amidate, amidinate, β-diketiminate) versus cationic (diimine, NHC) complexes, although discernible trends were less evident for calculated kinetic barriers. The deoxygenation of the nitroso oxygen of the nitrosobenzene complex to form a copper-nitrene intermediate is postulated to be the rate-determining step. For the mechanism assumed in eqs 2 through 5, each step is exothermic. These individual steps are also calculated to possess reasonable kinetic barriers. Hence, copper-based complexes deserve consideration as potential catalysts for the phosgene-free synthesis of arylisocyanates from nitroaromatics.
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Application of the Correlation Consistent Composite Approach (ccCA) to Third-Row (Ga-Kr) Molecules
Date: January 19, 2008
Creator: DeYonker, Nathan J.; Mintz, Benjamin; Cundari, Thomas R., 1964- & Wilson, Angela K.
Description: This article discusses the application of the correlation consistent composite approach (ccCA). Abstract: The correlation consistent composite approach (ccCA) has been applied to the G3/05 training set of 51 energetic properties for the atoms and molecules that contain the 4p elements, Ga-Kr. When atomic and molecular first-order spin orbit coupling corrections are added to open shell atoms and molecules, the ccCA has a mean absolute deviation from experiment (MAD) of 0.95 kcal mol-1, an improvement of 0.10 kcal mol-1 over G3 and G3X model chemistries. The performance of the ccCA on third-row-containing atoms and molecules is, therefore, commensurate in accuracy with previous studies on lighter main group elements H-Ar. While the typical methods used to compute theoretical molecular spin orbit corrections may go against the spirit of "black box" model chemistries, such corrections may be necessary for molecules containing heavy elements such as Ga-Kr. For example, when second-order spin orbit corrections are added to the atomic and molecular energies, the ccCA MAD is reduced to 0.88 kcal mol-1.
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Accurate Enthalpies of Formation of Alkali and Alkaline Earth Metal Oxides and Hydroxides: Assessment of the Correlation Consistent Composite Approach (ccCA)
Date: July 12, 2006
Creator: Ho, Dustin S.; DeYonker, Nathan J.; Cundari, Thomas R., 1964- & Wilson, Angela K.
Description: This article discusses accurate enthalpies of formation of alkali and alkaline earth metal oxides and hydroxides. Abstract: Computing the enthalpies of formation for alkali metal and alkaline earth metal oxides (MₓO) and hydroxides [M(OH)n] using the Gaussian-n (Gn) and Weismann-n (Wn) ab initio model chemistries is difficult due to an improper treatment of core-valence electron correlation effects. Using a new model chemistry called the correlation consistent Composite Approach (ccCA), enthalpies of formation were determined for eight different alkali/alkaline earth metal oxides and hydroxides. Unlike the Gn and Wn model chemistries, which must be modified to properly account for core-valence electron correlation, the standard implementations of the ccCA provide acceptable results, and all enthalpies of formation obtained with the ccCA are within the accepted range of recommended values.
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Redox Activation of Alkene Ligands in Platinum Complexes with Non-innocent Ligands
Date: December 19, 2009
Creator: Boyer, Julie L.; Cundari, Thomas R., 1964-; DeYonker, Nathan J.; Rauchfuss, Thomas B. & Wilson, Scott R.
Description: This article discusses redox activation of alkene ligands. The reactivity of metal olefin complexes with non-innocent ligands (NILs) was examined. Treatment of PtCl2(diene) with the deprotonated catechol or aminophenol ligands afforded the corresponding Pt(NIL)(diene) complexes. The Pt(ͭBAfPh)(COD), Pt(tBAfPh)(nbd), and Pt(O2C6H2tBu2)(COD) (H2tBAfPh = 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, H2O2C6H2tBu2 = 3,5-di-tert-butylcatechol) complexes were examined by cyclic voltammetry. Treatment of Pt(tBAfPh)(COD) or Pt(tBAfPh)(ndb) with AgPF6 afforded the imino-semiquinones [Pt(tBAfPh)(COD)] PF6 or [Pt(tBAfPh)(nbd)]PF6 respectively. The [Pt(tBAfPh)(COD)] complex was unreactive toward nucleophiles, whereas the oxidized derivative, [Pt(tBAfPh)(COD)]PF6, rapidly and stereospecifically added alkoxides at the carbon trans to the phenolate. The Pt(tBAfPh)(COD), [Pt(tBAfPh)(COD)]PF6, Pt(tBAfPh)(C8H12OMe), and [Cp2Co][Pt-(tBAfPh)(C8H12OMe)] complexes were characterized crystallographically.
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Quantitative Computational Thermochemistry of Transition Metal Species
Date: May 15, 2007
Creator: DeYonker, Nathan J.; Peterson, Kirk A.; Steyl, Gideon; Wilson, Angela K. & Cundari, Thomas R., 1964-
Description: This article discusses quantitative computational thermochemistry of transition metal species. The correlation consistent Composite Approach (ccCA), which has been shown to achieve chemical accuracy (±1 kcal mol⁻¹) for a large benchmark set of main group and s-block metal compounds, is used to compute enthalpies of formation for a set of 17 3d transition metal species. The training set includes a variety of metals, ligands, and bonding types. Using the correlation consistent basis sets for the 3d transition metals, the authors find that gas-phase enthalpies of formation can be efficiently calculated for inorganic and organometallic molecules with ccCA. However, until the reliability of gas-phase transition metal thermochemistry is improved, both experimentally and theoretically, a large experimental training set where uncertainties are near ±1 kcal mol⁻¹ (akin to commonly used main group benchmarking sets) remains an ambitious goal. For now, an average deviation of ±3 kcal mol⁻¹ appears to be the initial goal of "chemical accuracy" for ab initio transition metal model chemistries. The ccCA is also compared to a more robust but relatively expensive composite approach primarily utilizing large basis set coupled cluster computations. For a smaller training set of eight molecules, ccCA has a mean absolute deviation (MAD) of 3.4 ...
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Performance of the correlation consistent composite approach for transition states: A comparison to G3B theory
Date: October 19, 2007
Creator: Grimes, Thomas V.; Wilson, Angela K.; DeYonker, Nathan J. & Cundari, Thomas R., 1964-
Description: This article discusses performance of the correlation consistent composite approach for transition states. The correlation consistent composite approach (ccCA) was applied to the prediction of reaction barrier heights (i.e., transition state energy relative to reactants and products) for a standard benchmark set of reactions comprised of both hydrogen transfer reactions and nonhydrogen transfer reactions (i.e., heavy-atom transfer, Sn2, and unimolecular reactions). The ccCA method was compared against G3B for the same set of reactions. Error metrics indicate that ccCA achieves "chemical accuracy" with a mean unsigned error (MUE) of 0.89 kcal/mol with respect to the benchmark data for barrier heights; G3B has a mean unsigned error of 1.94 kcal/mol. Further, the greater accuracy of ccCA for predicted reaction barriers is compared to other benchmarked literature methods, including density functional (BB1K, MUE=1.16 kcal/mol) and wavefunction-based [QCISD(T), MUE=1.10 kcal/mol] methods.
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Combined Experimental and Computational Studies on the Nature of Aromatic C-H Activation by Octahedral Ruthenium(II) Complexes: Evidence for σ-Bond Metathesis from Hammett Studies
Date: November 27, 2007
Creator: DeYonker, Nathan J.; Foley, Nicholas A.; Cundari, Thomas R., 1964-; Gunnoe, T. Brent & Petersen, Jeffrey L.
Description: This article discusses combined experimental and computational studies on the nature of aromatic C-H activation by octahedral ruthenium(II) complexes. Abstract: Octahedral ruthenium complexes of the type TpRu(L)(NCMe)R [Tp = hydridotris(pyrazolyl)borate; R = alkyl or aryl; L = CO or PMe3] have been shown previously to initiate the C-H activation of aromatic substrates. In order to probe the nature of the C-H activation step, reaction rates have been theoretically obtained for the conversion of TpRu(L)(ƞ2-C,C-C6H5X)Me to TpRu(L)(ρ-C6H4X) and CH4 where X is varied among Br, Cl, CN, F, H, NH2, NO2, and OMe. A linear Hammett correlation is calculated with a positive ρ value of 2.6 for L = CO and 3.2 for L = PMe3. Calculated kinetic data for the aromatic C-H activations indicate that an electrophilic aromatic substitution mechanism is unlikely. While experiments cannot fully replicate the entire range of calculated Hammett plots, reactivity trends are consistent with the calculations that suggest activation barriers to overall metal-mediated arene C-H bond cleavage are reduced by the presence of electron-withdrawing groups in the position para to the site of activation. Previous mechanistic studies, as well as the structure and imaginary vibrational modes of the present transition states, validate that the C-H ...
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The correlation-consistent composite approach: Application to the G3/99 test set
Date: September 13, 2006
Creator: DeYonker, Nathan J.; Grimes, Thomas V.; Yockel, Scott; Dinescu, Adriana; Mintz, Benjamin; Cundari, Thomas R., 1964- et al
Description: This article discusses the correlation-consistent composite approach. Abstract: The correlation-consistent composite approach (ccCA), 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 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 molˉ¹), and a 0.96 kcal molˉ¹ 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.
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