Fermín Huarte-Larrañaga

Accurate 3 dimensional quantum dynamical study of the Ne+H2+→NeH++H reaction

In this work a comprehensive, fully converged coupled states (CS) quantum mechanical (QM) study of the endothermic Ne+H2+ ion-molecule reaction is presented. The computed dynamical properties are compared with quasi-classical trajectory (QCT) and with the available experimental data. To this end, the analytical potential energy surface of Pendergast, Heck, Hayes, and Jacquet was employed. The two main features of the dynamical behavior for this system are: (1) the rich structure present in the state-selected integral cross section energy-dependent curves, which may be attributed to resonances surviving the partial wave summation; and (2) the large differences between the quantum and the QCT cross sections which are caused by the inability of classical mechanics to conserve the zero point energy. Also noteworthy are the strong enhancement of the reactivity due to higher vibrational states and the effect of the activated complex, formed during the reaction process, on the angular and the rotational distribu...

THE APPLICATION OF COMPLEX ABSORBING POTENTIALS TO AN INVARIANT EMBEDDING SCATTERING METHOD: I. THEORY AND COMPUTATIONAL DETAILS

In this article, an extension of quantum scattering methods based on propagative R-matrix techniques to deal with negative imaginary potentials is presented. Reactive probabilities can be then obtained, considering only the reactants arrangement channel and Jacobi coordinates. It has been necessary to generalize the R-matrix propagation method, in order to consider the complex-valued nature of the interaction matrix. The new formulation has been particularized, in the present case, to the Infinite-Order Sudden Approximation, for which several results, focusing on the reliability and numerical performances of the method, will be shown.

Exact quantum 3D cross sections for the Ne+H2+→NeH++H reaction by the hyperspherical method. Comparison with approximate quantum mechanical and classical results

Exact, fully converged three-dimensional quantum mechanical cross sections for the title reaction have been computed on the analytical potential energy surface of Pendergast, Heck, Hayes and Jaquet. The close-coupling hyperspherical method of Launay and LeDourneuf has been used for the calculations. Results explicitly shown here correspond to reaction probabilities as a function of total energy and J, integral cross sections and product rotational distributions, for the first three reactant vibrational levels and the ground j=0 reactant rotational level. Integral cross sections confirm the main experimental findings: (a) vibrational excitation greatly enhances reactivity and (b) the reactivity threshold is near the opening of the v=2 reactant channel. Product rotational distributions show an unimodal shape, with its maximum lying at intermediate values of the open product rotational quantum numbers. Results have been compared with previously available centrifugal sudden (CS) and reactive infinite order sudden (R-IOS) results, as well as with quasiclassical trajectory (QCT) calculations. As a general trend, CS and R-IOS integral cross sections show the same qualitative shape as the exact ones, the CS ones being very close to exact but those of R-IOS are between four and five times lower. The QCT results are three times lower and fail to reproduce the threshold behaviour. CS rotational distributions are slightly hotter than exact ones, while QCT results are closer to the exact ones except for the fact that they populate rotational levels not allowed when considering both the zero-point energy and the total energy conservation.

On the accuracy of reactive scattering calculations with absorbing potentials: a new implementation based on a generalized R-matrix propagation

Abstract A quantum scattering method based on combining a generalization of the propagative R-matrix technique with negative imaginary potentials is presented. Reactive probabilities are then obtained considering only the reactants arrangement channel and Jacobi coordinates. Collinear and infinite order sudden results are shown for the Cl+HCl symmetric reaction, showing excellent agreement with previous results, including the reproduction of sharp reactive scattering resonances, at a fraction of the computer time and memory requirements.

Thermal rate coefficients in collinear versus bent transition state reactions: the N+N2 case study

Zero total angular momentum exact quantum calculations of the probabilities of the N+N2 reaction have been performed on the L3 potential energy surface having a bent transition state. This has allowed us to work out J-shifting estimates of the thermal rate coefficient based on the calculation of either detailed (state-to-state) or cumulative (multiconfiguration) probabilities. The results obtained are used to compare the numerical outcomes and the concurrent computational machineries of both quantum and semiclassical approaches as well as to exploit the potentialities of the J-shifting model. The implications of moving the barrier to reaction from the previously proposed collinear geometry of the LEPS to the bent one of L3 are also investigated by comparing the related detailed reactive probabilities.

An extension of the grid empowered molecular simulator to quantum reactive scattering.

Within the activities of the D37 COST Action, we have further developed the quantum dynamics framework of the grid empowered molecular simulator (GEMS) implemented on the segment of the European grid available to the COMPCHEM (computational chemistry) virtual organization. GEMS does now include in a full ab initio approach, the evaluation of the detailed quantum (both time dependent and time independent) dynamics of small systems starting from the calculation of the electronic structure properties as well as the direct calculation of thermalized properties. Illustrative, full dimensional applications of the extended simulator to the H + H2, N + N2, and O + O2 systems are presented.

The application of complex absorbing potentials to an invariant embedding scattering method. II. Applications

The application to several triatomic reactions of a novel implementation of absorbing potentials on a generalized R-matrix propagation method [Chem. Phys. Lett. 291, 346 (1998) and J. Chem. Phys. 109, 5761 (1998)] is presented. Specific systems chosen have been Li+FH, Mg+FH and H+F2, so that an extensive application covering a wide range of potential energy surfaces (PESs) has been performed: it includes moderately and largely exoergic and endoergic processes, simple and involved PES, moderate to large skew angles, and direct and complex-forming collisions. In all cases, it is shown that the use of the absorbing potential is simple and robust, yielding correct values at a fraction of the computer’s resources consumption. The best effectiveness is obtained for exothermic, direct reactions, for which up to one order of magnitude in CPU time saving is obtained. This efficiency opened the possibility for a very detailed exploration of the reactive process, in particular on those quantities strongly dependent ...

5D quantum dynamics of the H2@SWNT system: Quantitative study of the rotational-translational coupling

The dynamics of the dihydrogen molecule when confined in carbon nanotubes with different chiralities and diameters are studied by using a 5 dimensional model considering the most relevant degrees of freedom of the system. The nuclear eigenstates are calculated for an (8,0) and a (5,0) carbon nanotubes by the State-Average Multiconfigurational Time-dependent Hartree, and then studied using qualitative tools (mapping of the total wave functions onto given subspaces) and more rigorous analysis (different kinds of overlaps with reference functions). The qualitative analysis is seen to fail due to a strong coupling between the internal and translational degrees of freedom. Using more accurate tools allows us to gain a deeper insight into the behaviour of confined species.

A molecular dynamics study of the evolution from the formation of the {\text {C}}_{6}{\text {F}}_{6}–({\text {H}}_{2}{\text {O}})_{n} small aggregates to the {\text {C}}_{6}{\text {F}}_{6} solvation

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