Vibrational, non-adiabatic and isotopic effects in the dynamics of the H2 + H2+ → H3+ + H reaction: application to plasma modelling

The title reaction is studied using a quasi-classical trajectory method for collision energies between 0.1 meV and 10 eV, considering the vibrational excitation of H+2 reactant. A new potential energy surface is developed based on a Neural Network many body correction of a triatomics-in-molecules potential, which significantly improves the accuracy of the potential up to energies of 17 eV, higher than in other previous fits. The effect of the fit accuracy and the non-adiabatic transitions on the dynamics are analysed in detail. The reaction cross section for collision energies above 1 eV increases significantly with the increasing of the vibrational excitation of H+2(v'), for values up to v'=6. The total reaction cross section (including the double fragmentation channel) obtained for v'=6 matches the new experimental results obtained by Savic, Schlemmer and Gerlich [Chem. Phys. Chem. 21 (13), 1429.1435 (2020). doi:10.1002/cphc.v21.13]. The differences among several experimental setups, for collision energies above 1 eV, showing cross sections scattered/dispersed over a rather wide interval, can be explained by the differences in the vibrational excitations obtained in the formation of H+2 reactants. On the contrary, for collision energies below 1 eV, the cross section is determined by the long range behaviour of the potential and do not depend strongly on the vibrational state of H+2. In addition in this study, the calculated reaction cross sections are used in a plasma model and compared with previous results. We conclude that the efficiency of the formation of H+3 in the plasma is affected by the potential energy surface used

Vibrational, non-adiabatic and isotopic effects in the dynamics of the H2 + H2+ → H3+ + H reaction: application to plasma modelling

The title reaction is studied using a quasi-classical trajectory method for collision energies between 0.1 meV and 10 eV, considering the vibrational excitation of (Formula presented.) reactant. A new potential energy surface is developed based on a Neural Network many body correction of a triatomics-in-molecules potential, which significantly improves the accuracy of the potential up to energies of 17 eV, higher than in other previous fits. The effect of the fit accuracy and the non-adiabatic transitions on the dynamics are analysed in detail. The reaction cross section for collision energies above 1 eV increases significantly with the increasing of the vibrational excitation of (Formula presented.) ((Formula presented.)), for values up to (Formula presented.) =6. The total reaction cross section (including the double fragmentation channel) obtained for (Formula presented.) =6 matches the new experimental results obtained by Savic, Schlemmer and Gerlich [Chem. Phys. Chem. 21 (13), 1429.1435 (2020). doi:10.1002/cphc.v21.13]. The differences among several experimental setups, for collision energies above 1 eV, showing cross sections scattered/dispersed over a rather wide interval, can be explained by the differences in the vibrational excitations obtained in the formation of (Formula presented.) reactants. On the contrary, for collision energies below 1 eV, the cross section is determined by the long range behaviour of the potential and do not depend strongly on the vibrational state of (Formula presented.). In addition in this study, the calculated reaction cross sections are used in a plasma model and compared with previous results. We conclude that the efficiency of the formation of (Formula presented.) in the plasma is affected by the potential energy surface use

Superficie de energía potencial y dinámica para la reacción H2CO + OH

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de lectura: 25-01-2021Esta tesis tiene embargado el acceso al texto completo hasta el 25-07-202

Variational principle to regularize machine-learned density functionals: The non-interacting kinetic-energy functional

Practical density functional theory (DFT) owes its success to the groundbreaking work of Kohn and Sham that introduced the exact calculation of the non-interacting kinetic energy of the electrons using an auxiliary mean-field system. However, the full power of DFT will not be unleashed until the exact relationship between the electron density and the non-interacting kinetic energy is found. Various attempts have been made to approximate this functional, similar to the exchange-correlation functional, with much less success due to the larger contribution of kinetic energy and its more non-local nature. In this work, we propose a new and efficient regularization method to train density functionals based on deep neural networks, with particular interest in the kinetic-energy functional. The method is tested on (effectively) one-dimensional systems, including the hydrogen chain, non-interacting electrons, and atoms of the first two periods, with excellent results. For atomic systems, the generalizability of the regularization method is demonstrated by training also an exchange-correlation functional, and the contrasting nature of the two functionals is discussed from a machine-learning perspectiveThe authors acknowledge the funding from the German Ministry for Education and Research (Berlin Institute for the Foundations of Learning and Data, BIFOLD). P.d.M.S. acknowl edges the funding from MICINN (Spain) under Grant Nos.PID2021-122549NB-C21 and PID2021-122549NB-C2

Neural network potential energy surface for the low temperature ring polymer molecular dynamics of the H2CO + OH reaction

14 pags., 12 figs., 2 tabs.A new potential energy surface (PES) and dynamical study of the reactive process of H2CO + OH toward the formation of HCO + H2O and HCOOH + H are presented. In this work, a source of spurious long range interactions in symmetry adapted neural network (NN) schemes is identified, which prevents their direct application for low temperature dynamical studies. For this reason, a partition of the PES into a diabatic matrix plus a NN many-body term has been used, fitted with a novel artificial neural network scheme that prevents spurious asymptotic interactions. Quasi-classical trajectory (QCT) and ring polymer molecular dynamics (RPMD) studies have been carried on this PES to evaluate the rate constant temperature dependence for the different reactive processes, showing good agreement with the available experimental data. Of special interest is the analysis of the previously identified trapping mechanism in the RPMD study, which can be attributed to spurious resonances associated with excitations of the normal modes of the ring polymer.This research was funded by the MICIU (Spain) under Grant No. FIS2017-83473-C2. We also acknowledge computing time at Finisterre (CESGA) and MareNostrum (BSC) under the RES computational grant (Nos. ACCT-2019-3-0004 and AECT-2020-1- 0003)

Artificial Neural Network Potential Energy Surface for H2CO+OH reaction

IMAMPC2019, Madrid, 11 - 14 June, 2019Peer reviewe

Quantum Roaming in the Complex-Forming Mechanism of the Reactions of OH with Formaldehyde and Methanol at Low Temperature and Zero Pressure: A Ring Polymer Molecular Dynamics Approach

8 pags., 5 figs., 1 tab.The quantum dynamics of the title reactions are studied using the ring polymer molecular dynamics (RPMD) method from 20 to 1200 K using recently proposed full dimensional potential energy surfaces which include long-range dipole-dipole interactions. A V-shaped dependence of the reaction rate constants is found with a minimum at 200-300 K, in rather good agreement with the current experimental data. For temperatures above 300 K the reaction proceeds following a direct H-abstraction mechanism. However, below 100 K the reaction proceeds via organic-molecule···OH collision complexes, with very long lifetimes, longer than 10 s, associated with quantum roaming arising from the inclusion of quantum effects by the use of RPMD. The long lifetimes of these complexes are comparable to the time scale of the tunnelling to form reaction products. These complexes are formed at zero pressure because of quantum effects and not only at high pressure as suggested by transition state theory (TST) calculations for OH + methanol and other OH reactions. The zero-pressure rate constants reproduce quite well measured ones below 200 K, and this agreement opens the question of how important the pressure effects on the reaction rate constants are, as implied in TST-like formalisms. The zero-pressure mechanism is applicable only to very low gas density environments, such as the interstellar medium, which are not repeatable by experiments.P.d.M.-S., A.A., E.J., and O.R. acknowledge the support of the Ministerio de Economıa y Competitividad (SPAIN) under ́ Grant No. FIS2017-83473-C2 and from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. 610256 (NANOCOSMOS). Y.V.S. acknowledges the support of the European Regional Development Fund and the Republic of Cyprus through the Research Promotion Foundation (Project: INFRASTRUCTURE/1216/0070). The calculations have been performed at CESGA (finisterrae2), CENITS (lusitania2), and SCAYLE (calendula) supercomputer centers under RES (Red Española de Supercomputacion) computational Grant Nos. AECT-2018-2-0001, AECT- ́2018-3-0001, and AECT-2019-1-0001