We have applied the multicoefficient density functional theory (MC-DFT) to four recent Minnesota functionals, including M06-2X, M08-HX, M11, and MN12-SX on the performance of thermochemical kinetics. The results indicated that the accuracy can be improved significantly using more than one basis set. We further included the SCS-MP2 energies into MC-DFT, and the resulting mean unsigned errors (MUEs) decreased by approximately 0.3 kcal/mol for the most accurate basis set combinations. The M06-2X functional with the simple [6-311+G(d,p)/6-311+G(2d,2p)] combination gave the best performance/cost ratios for the MC-DFT and MC-SCS-MP2|MC-DFT methods with MUE of 1.58 and 1.22 kcal/mol, respectively.
High-level correlated electronic structure calculation and dual-level variational transition state theory with multidimensional tunneling calculation for rate constants have been performed on four noble gas exchange reactions [(1) He + HNBHe'(+) → He' + HNBHe(+), (2) He + HNBNe(+) → Ne + HNBHe(+), (3) Ne + HNBNe'(+) → Ne' + HNBNe(+), and (4) Ar + HNBAr'(+) → Ar' + HNBAr(+)] and on three (3)He isotopic analogues (He + HNB(3)He(+), (3)He + HNBHe(+), and (3)He + HNB(3)He(+)) of the first reaction. The classical barrier heights were predicted to be 8.9, 6.8, 5.7, and 5.5 kcal/mol for the four reactions, respectively. The tunneling effects were found to be important below 250 K for the He reactions and below 150 K for the Ne and Ar reactions. Kinetic helium isotope effects as large as 7.8 at 100 K were predicted for the (3)He + HNB(3)He(+) reaction. Additionally, the structures and energies of the Kr + HNBKr'(+) and Xe + HNBXe'(+) systems have also been studied.
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