Journal ArticleDOI
Accurate vibrational-rotational partition functions and standard-state free energy values for H2O2 from Monte Carlo path-integral calculations.
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TLDR
The calculations employed enhanced-same-path extrapolation of trapezoidal Trotter Fourier path integrals, and the paths were constructed using fast Fourier sine transforms, and adaptively optimized stratified sampling was used in configuration space.Abstract:
Accurate quantum mechanical partition functions and absolute free energies of H2O2 are determined using a realistic potential energy surface [J. Koput, S. Carter, and N. C. Handy, J. Phys. Chem. A 102, 6325 (1998)] for temperatures ranging from 300 to 2400 K by using Monte Carlo path integral calculations with new, efficient polyatomic importance sampling methods. The path centroids are sampled in Jacobi coordinates via a set of independent ziggurat schemes. The calculations employed enhanced-same-path extrapolation of trapezoidal Trotter Fourier path integrals, and the paths were constructed using fast Fourier sine transforms. Importance sampling was also used in Fourier coefficient space, and adaptively optimized stratified sampling was used in configuration space. The free energy values obtained from the path-integral calculations are compared to separable-mode approximations, to the Pitzer–Gwinn approximation, and to values in thermodynamic tables. Our calculations support the recently proposed revisi...read more
Citations
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Journal ArticleDOI
Modeling the Kinetics of Bimolecular Reactions
Antonio Fernández-Ramos,James A. Miller,Stephen J. Klippenstein,Stephen J. Klippenstein,Donald G. Truhlar +4 more
TL;DR: This review is concerned with the theoretical and computational modeling of bimolecular reactions, especially with generally applicable methods for kinetics (i.e., overall rates as opposed to detailed dynamics), and includes a basic theoretical framework that can be used for gas-phase thermal reactions, gas- phase microcanonical and state-selected reactions, and condensed-phase chemical reactions.
Journal ArticleDOI
Practical methods for including torsional anharmonicity in thermochemical calculations on complex molecules: the internal-coordinate multi-structural approximation.
TL;DR: A new class of methods, called multi-structural (MS) methods, is presented that circumvents the need for such assignments by instead adjusting the harmonic results by torsional correction factors that are determined using internal coordinates.
Journal ArticleDOI
The 1-D hindered rotor approximation
TL;DR: An algorithm for consistently treating all tops in a molecule is developed, and simple codes which interface with electronic structure codes to provide thermochemical properties of individual species and reactions that have been corrected for internal rotations are presented.
Journal ArticleDOI
Statistical thermodynamics of bond torsional modes: tests of separable, almost-separable, and improved Pitzer-Gwinn approximations.
TL;DR: Practical approximation schemes for calculating partition functions of torsional modes are tested against accurate quantum mechanical results for H(2)O( 2) and six isotopically substituted hydrogen peroxides and the effectiveness of these methods for the calculation of isotope effects is studied.
Journal ArticleDOI
Exploring the effect of anharmonicity of molecular vibrations on thermodynamic properties.
Bosiljka Njegic,Mark S. Gordon +1 more
TL;DR: It is found that the anharmonicity and coupling of molecular vibrations can play a significant role in predicting accurate thermodynamic quantities.
References
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Book
Quantum Mechanics and Path Integrals
TL;DR: Au sommaire as discussed by the authors developed the concepts of quantum mechanics with special examples and developed the perturbation method in quantum mechanics and the variational method for probability problems in quantum physics.
Book
Techniques and Applications of Path Integration
TL;DR: In this paper, the authors present a list of applications of the path integral formula in statistical mechanics, including the application of the Path Integral formula to Statistical Mechanics, asymptotic analysis, and the phase space path integral.