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The reaction rate rises and falls with increasing density or friction when a molecule is activated by collisions with the solvent particles. This so-called Kramers turnover has recently been observed in the isomerization reaction of LiCN in an argon bath. In this paper, we demonstrate by direct comparison with those results that a reduced-dimensional (generalized) Langevin description gives rise to similar reaction dynamics as the corresponding (computationally expensive) full molecular dynamics calculations. We show that the density distributions within the Langevin description are in direct agreement with the full molecular dynamics results and that the turnover in the reaction rates is reproduced qualitatively and quantitatively at different temperatures. [ABSTRACT FROM AUTHOR]

In this paper, we present a detailed study on the application of the quantum control technique of navigation in the energy spectrum to chemical isomerization processes, namely, CN-Li Li-CN. This technique is based on the controlled time variation of a Hamiltonian parameter, an external uniform electric field in our case. The main result of our work establishes that the navigation involved in the method is robust, in the sense that quite sizable deviations from a pre-established control parameter time profile can be introduced and still get good final results. This is specially relevant thinking of a experimental implementation of the method. [ABSTRACT FROM AUTHOR]

The isomerization between CN-Li and Li-CN in an argon bath provides a paradigmatic example of a reaction in a solvent with tunable coupling. In previous work, we found that the rates exhibited a turnover with the density of the argon bath in the limit that the CN bond was held fixed [P. L. Garcia- Muller, R. Hernandez, R. M. Benito, and F. Borondo, J. Chem. Phys. 137, 204301 (2012)]. Here, we report the effect of the CN bond vibration on the dynamics and the persistence of the turnover. As hypothesized earlier, the CN bond is indeed weakly coupled with the reaction path despite the presence of the argon cage. [ABSTRACT FROM AUTHOR]

According to Kramers, rates of molecular process are expected to follow a rise and fall from low friction (at little to no interaction with the environment) to high friction (at typical liquid densities and above). This so-called Kramers turnover was recently observed and delineated in the case of the LiNC<=>LiCN isomerization reaction in the presence of an argon bath [P. García-Müller, R. Hernandez, R. M. Benito, and F. Borondo, Phys. Rev. Lett. 101, 178302 (2008)]. The rates were obtained using direct molecular dynamics of an all-atom representation and the Langevin dynamics of a projected representation. We now provide further evidence that the forward and backward rates are indeed exhibiting the turnover. The rates are also seen to agree remarkably well with the Pollak-Grabert-Hänggi rate formulas in regimes satisfying the theory underlying assumptions. At higher temperatures, when the theory is expected to fail, the solvated LiCN isomerization continues to exhibit activated dynamics following the turnover. [ABSTRACT FROM AUTHOR]

The dynamics of the isomerization reaction LiNC...LiCN is considered at a quantum level. This study is performed with the aid of dynamically localized wave packets, which provide a wealth of information about the relevant parts of the molecular phase space. Three cases are considered, corresponding to energies close to the threshold for isomerization. The initial position of the packet is always localized in the LiNC well (which is the most stable), and different energies and distributions among the vibrational modes of the molecule are used. The packet will then explore phase space and, as a result of these dynamics, different time scales (including those from intramolecular energy transfer processes) exist, which appear in the low resolution features of the corresponding spectra. The characteristics of these spectra are discussed and analyzed using a variety of techniques, making extensive use of the ideas of nonlinear dynamics, and the conditions for the applicability of statistical theories to evaluate reaction rates in this case are considered. [ABSTRACT FROM AUTHOR]

The transitory and stationary behavior of a quantum chaotic ratchet consisting of a biharmonic potential under the effect of different drivings in contact with a thermal environment is studied. For weak forcing and finite ħ, we identify a strong dependence of the current on the structure of the chaotic region. Moreover, we have determined the robustness of the current against thermal fluctuations in the very weak coupling regime. In the case of strong forcing, the current is determined by the shape of a chaotic attractor. In both cases the temperature quickly stabilizes the ratchet, but in the latter. it also destroys the asymmetry responsible for the current generation. Finally, applications to isomerization reactions are discussed. [ABSTRACT FROM AUTHOR]

We explore here the feasibility of using the recently introduced Lagrangian descriptors [A. M. Mancho et al., Commun. Nonlinear Sci. Numer. Simul. 18, 3530 (2013)] to unveil the usually rich dynamics taking place in the vibrations of molecular systems, especially if they are floppy. The principal novelty of our work is the inclusion of p norms in the definition of the descriptors in this kind of system, which greatly enhances their power to discern among the different structures existing in the phase space. As an illustration we use the LiCN molecule described by realistic potentials in two and three dimensions, which exhibits chaotic motion within a mixed phase space in the isomerization between the two wells corresponding to the linear isomer stable configurations, LiNC and LiCN. In particular, we pay special attention to the manifolds emerging from the unstable fixed point between the corresponding isomer wells, and also to the marginally stable structures around a parabolic point existing near the LiNC well. [ABSTRACT FROM AUTHOR]

The performance of a recently proposed method to efficiently calculate scar functions is analyzed in problems of chemical interest. An application to the computation of wave functions associated with barriers relevant for the LiNC ⇄ LiCN isomerization reaction is presented as an illustration. These scar functions also constitute excellent elements for basis sets suitable for quantum calculation of vibrational energy levels. To illustrate their efficiency, a calculation of the LiNC/LiCN eigenfunctions is also presented. [ABSTRACT FROM AUTHOR]

Abstract: We explore the applicability to manipulate chemical reactions of a particularly simple method of quantum control that has been recently proposed in the literature . For this purpose we use a realistic model for the isomerization of LiNC. [ABSTRACT FROM AUTHOR]

The accuracy of rate constants calculated using transition state theory depends crucially on the correct identification of a recrossing-free dividing surface. We show here that it is possible to define such optimal dividing surface in systems with non-Markovian friction. However, a more direct approach to rate calculation is based on invariant manifolds and avoids the use of a dividing surface altogether, Using that method we obtain an explicit expression for the rate of crossing an anharmonic potential barrier. The excellent performance of our method is illustrated with an application to a realistic model for LiNC ... LiCN isomerization. [ABSTRACT FROM AUTHOR]