Path-dependent variational effects and multidimensional tunneling in multi-path variational transition state theory: rate constants calculated for the reactions of HO2 with tert-butanol by including all 46 paths for abstraction at C and all six paths for abstraction at O.

Multi-path variational transition state theory (MP-VTST) provides a conformationally complete framework for calculating gas-phase rate constants. For reactions in which the transition state has distinguishable torsional minima (which include most reactions), there are multiple possible reaction paths. In principle MP-VTST includes the contributions from all the reaction paths, and it should explicitly treat the variational and tunneling effects of each path, but in practice one may need to truncate the number of paths included in MP-VTST calculations in order to achieve a balance between computational cost and accuracy. In this work, we present calculations including all paths for two prototype combustion reactions, namely the two hydrogen abstraction reactions from tert-butanol by HO2 radical. For both reactions we included all the reaction paths. Since abstraction at C has 46 paths, it provided a good opportunity to carry out a case study in which we investigated the errors introduced by truncating the number of paths. For the reaction studied, we found that the variational and multidimensional tunneling transmission coefficients are very different for different reaction paths, which provides new evidence that MP-VTST is necessary for treating path-dependent variational effects and multidimensional tunneling. We found that tunneling transmission coefficients can be much larger for higher-energy paths than for lower-energy ones. Interestingly, the simple hypothesis that higher barriers are narrower does not explain this finding in the present case; we found instead that the effect is due to higher-energy barriers having the possibility of tunneling at energies farther below the barrier top. We also show that a previously applied criterion for judging convergence with respect to the number of paths may not be reliable at low temperature.

[1]  D. Truhlar,et al.  Nanodusty plasma chemistry: a mechanistic and variational transition state theory study of the initial steps of silyl anion-silane and silylene anion-silane polymerization reactions. , 2015, Physical chemistry chemical physics : PCCP.

[2]  D. Truhlar,et al.  Prediction of experimentally unavailable product branching ratios for biofuel combustion: the role of anharmonicity in the reaction of isobutanol with OH. , 2014, Journal of the American Chemical Society.

[3]  D. Truhlar,et al.  Quantum Thermochemistry: Multistructural Method with Torsional Anharmonicity Based on a Coupled Torsional Potential. , 2013, Journal of chemical theory and computation.

[4]  D. Truhlar,et al.  Kinetics of the hydrogen atom abstraction reactions from 1-butanol by hydroxyl radical: theory matches experiment and more. , 2013, The journal of physical chemistry. A.

[5]  D. Truhlar,et al.  Biofuel combustion. Energetics and kinetics of hydrogen abstraction from carbon-1 in n-butanol by the hydroperoxyl radical calculated by coupled cluster and density functional theories and multistructural variational transition-state theory with multidimensional tunneling. , 2012, The journal of physical chemistry. A.

[6]  D. Truhlar,et al.  Multistructural variational transition state theory: kinetics of the hydrogen abstraction from carbon-2 of 2-methyl-1-propanol by hydroperoxyl radical including all structures and torsional anharmonicity. , 2012, The journal of physical chemistry. A.

[7]  D. Truhlar,et al.  Multi-path variational transition state theory for chemical reaction rates of complex polyatomic species: ethanol + OH reactions. , 2012, Faraday discussions.

[8]  S. M. Sarathy,et al.  A comprehensive chemical kinetic combustion model for the four butanol isomers , 2012 .

[9]  D. Truhlar,et al.  Multipath variational transition state theory: rate constant of the 1,4-hydrogen shift isomerization of the 2-cyclohexylethyl radical. , 2012, The journal of physical chemistry. A.

[10]  Donald G Truhlar,et al.  Kinetics of the Hydrogen Abstraction from Carbon-3 of 1-Butanol by Hydroperoxyl Radical: Multi-Structural Variational Transition-State Calculations of a Reaction with 262 Conformations of the Transition State. , 2012, The journal of physical chemistry letters.

[11]  D. Truhlar,et al.  Multi-structural variational transition state theory. Kinetics of the 1,4-hydrogen shift isomerization of the pentyl radical with torsional anharmonicity , 2011 .

[12]  D. Truhlar,et al.  Convergent Partially Augmented Basis Sets for Post-Hartree-Fock Calculations of Molecular Properties and Reaction Barrier Heights. , 2011, Journal of chemical theory and computation.

[13]  Donald G Truhlar,et al.  Computational Thermochemistry: Scale Factor Databases and Scale Factors for Vibrational Frequencies Obtained from Electronic Model Chemistries. , 2010, Journal of chemical theory and computation.

[14]  D. Truhlar,et al.  Kinetics of hydrogen-transfer isomerizations of butoxyl radicals. , 2010, Physical chemistry chemical physics : PCCP.

[15]  Hans-Joachim Werner,et al.  Simplified CCSD(T)-F12 methods: theory and benchmarks. , 2009, The Journal of chemical physics.

[16]  D. Truhlar,et al.  Exploring the Limit of Accuracy of the Global Hybrid Meta Density Functional for Main-Group Thermochemistry, Kinetics, and Noncovalent Interactions. , 2008, Journal of chemical theory and computation.

[17]  D. Truhlar,et al.  The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals , 2008 .

[18]  Donald G Truhlar,et al.  Density functionals with broad applicability in chemistry. , 2008, Accounts of chemical research.

[19]  Hans-Joachim Werner,et al.  A simple and efficient CCSD(T)-F12 approximation. , 2007, The Journal of chemical physics.

[20]  Yan Zhao,et al.  Exchange-correlation functional with broad accuracy for metallic and nonmetallic compounds, kinetics, and noncovalent interactions. , 2005, The Journal of chemical physics.

[21]  M. Karplus,et al.  How Enzymes Work: Analysis by Modern Rate Theory and Computer Simulations , 2004, Science.

[22]  Frederick R. Manby,et al.  Density fitting in second-order linear-r12 Møller–Plesset perturbation theory , 2003 .

[23]  Donald G. Truhlar,et al.  Effectiveness of Diffuse Basis Functions for Calculating Relative Energies by Density Functional Theory , 2003 .

[24]  D. Truhlar,et al.  Reaction-path dynamics in curvilinear internal coordinates including torsions , 1996 .

[25]  D. Truhlar,et al.  Reaction‐path potential and vibrational frequencies in terms of curvilinear internal coordinates , 1995 .

[26]  Donald G. Truhlar,et al.  Molecular modeling of the kinetic isotope effect for the [1,5]-sigmatropic rearrangement of cis-1,3-pentadiene , 1993 .

[27]  Donald G. Truhlar,et al.  POLYRATE 4: A new version of a computer program for the calculation of chemical reaction rates for polyatomics , 1992 .

[28]  B. C. Garrett,et al.  Transition State Theory , 1986 .

[29]  Donald G. Truhlar,et al.  Improved treatment of threshold contributions in variational transition-state theory , 1980 .

[30]  D. Truhlar.  Interpretation of the activation energy , 1978 .

[31]  D. Truhlar,et al.  Minimally augmented Karlsruhe basis sets , 2011 .

[32]  Hans-Heinrich Carstensen,et al.  Rate constants for the H abstraction from alkanes (R–H) by R′O2 radicals: A systematic study on the impact of R and R′ , 2007 .

[33]  Arnold Weissberger,et al.  Investigation of Rates and Mechanisms of Reactions , 1974 .

[34]  Donald G. Truhlar,et al.  EXACT TUNNELING CALCULATIONS. , 1971 .