Barriometry – an enhanced database of accurate barrier heights for gas-phase reactions

Abstract

The kinetics of many reactions are critically dependent upon the barrier heights for which accurate determination can be difficult. From the perspective of attaining such quantities using computational quantum chemistry, it is important to appropriately validate routine and efficient methodologies such as density functional theory (DFT) procedures. In the present study, we embark on the journey of establishing diverse databases using a consistent high-level quantum chemistry procedure, against which new and existing methodologies can be assessed. Thus, we have used the composite protocol W3X-L to provide more than 100 refined reference values for existing databases [e.g., Y. Zhao and D. G. Truhlar, J. Phys. Chem. A, 2005, 109, 5656] and additionally establish benchmark data that are of interest to atmospheric and combustion chemists. While our endeavor has just begun, assessment of various DFT methods with our existing results lends support to the use of MN15 as an adequate method for general kinetics applications. We also recommend the use of less-costly W2X and WG composite protocols for obtaining adequately accurate reference thermochemical values for larger molecular systems.

Highly Accurate CCSDT(Q)/CBS Reaction Barrier Heights for a Diverse Set of Transition Structures: Basis Set Convergence and Cost-Effective Approaches for Estimating Post-CCSD(T) Contributions

“…Normally, the CCSDT(Q) method is used for investigating relatively small transition structures (TSs) with pronounced multireference character. For instance, for reactions involving oxygen-rich species 25,26,27,28,29,30,31,32,33,34,35,36,37 and other small TSs. 38,39,40,41,42,43,44,45,46,47 The aim of the present work is to provide a systematic examination of basis set convergence of post-CCSD contributions (up to CCSDT(Q)) for a diverse set of reaction barrier heights.…”

The reHISS Three‐Range Exchange Functional with an Optimal Variation of Hartree–Fock and Its Use in the reHISSB‐D Density Functional Theory Method

“…The BDE262 set composes of the BDE261 set that contains a diverse collection of bond dissociation energies, plus the energy for splitting the (C 20 H 19 ) 2 dimer . We include in our additional assessments the ORBH36 set of reaction barriers related to atmospheric chemistry, CEPX33 set of proton‐exchange barriers and complexation energies, and the S12L set of noncovalent interactions for large complexes …”

“…These include mainly the E2 [27,28] and E3 [29,30] sets of diverse thermochemical properties. We further supplement these with the MS14 set of heats of formation of medium-sized molecules, [28] CHIE14 set of hydrocarbon ionization energies, [31] BDE262 set of bonddissociation energies, [32,33] FIR22 set of isodesmic-type reaction energies for fullerenes and related systems, [34][35][36] C24ISO set of C 24 H 12 isomerization energies, [31] S12L set of noncovalentinteraction energies, [37,38] ORBH36 set of barrier heights for oxygen-related reactions, [39] CEPX33 set of complexation energies and proton-exchange barriers, [40,41] and LF10 set of thermochemical quantities related to geometries and vibrational frequencies. [42,43] In general, we used the 6-311+G(3df,2p) basis set [44] in our single-point energy calculations, which we deem an appropriate compromise between accuracy and computational efficiency.…”

“…The BDE262 set composes of the BDE261 set [32] that contains a diverse collection of bond dissociation energies, plus the energy for splitting the (C 20 H 19 ) 2 dimer. [33] We include in our additional assessments the ORBH36 set of reaction barriers related to atmospheric chemistry, [39] CEPX33 set of protonexchange barriers and complexation energies, [40,41] and the S12L set of noncovalent interactions for large complexes. [37,38] Further to adding data to properties that are represented in the E3 set, we have evaluated the performance of the various functionals for obtaining molecular geometries and thermochemical quantities associated with the corresponding scaled harmonic vibrational frequencies.…”

BH9, a New Comprehensive Benchmark Dataset for Barrier Heights and Reaction Energies: Assessment of Density Functional Approximations and Basis Set Incompleteness Potentials

“…[33][34][35][36] Other benchmark sets either focus on specific types of reactions, or they contain only a handful of data points, or they are not evaluated using a reference level of enough quality to allow benchmarking commonly used quantum mechanical methods. 28,31,32,[37][38][39][40][41][42][43] The current necessity of a benchmark set for enzymatically catalyzed reactions has been emphasized several times recently. 31,32,44 Local correlation methods, particularly DLPNO-CCSD(T), have become very popular recently due to a favorable combination of relatively high accuracy and modest computational cost.…”