Pablo del Mazo‐Sevillano

Universidad Autónoma de Madrid

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Co-Authors

Octavio Roncero

Instituto de Física Fundamental

Alfredo Aguado

Universidad Autónoma de Madrid

Jan Hermann

Microsoft Research (India)

Daniel Félix-González

Universidad Autónoma de Madrid

J. R. Goicoechea

Consejo Superior de Investigaciones Científicas

Yury V. Suleimanov

American Association For The Advancement of Science

E. Roueff

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

J. Le Bourlot

Centre National de la Recherche Scientifique

ÉB

Émeric Bron

Centre National de la Recherche Scientifique

Franck Le Petit

Sorbonne Université

Cooperative Institutions

Centre National de la Recherche Scientifique

Consejo Superior de Investigaciones Científicas

Instituto de Física Fundamental

Universidad Autónoma de Madrid

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

Université Paris Sciences et Lettres

Observatoire de Paris

Sorbonne Université

Scuola Normale Superiore

Janssen (France)

Author Statistics

Papers

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

The Journal of Chemical Physics (2021)

Pablo del Mazo‐Sevillano Alfredo Aguado Octavio Roncero

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.

Spurious relationship

Diabatic

Potential energy surface

Matrix (chemical analysis)

10.1063/5.0044009

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Citations (21)

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

The Journal of Physical Chemistry Letters (2019)

Pablo del Mazo‐Sevillano Alfredo Aguado Elena Jiménez Yury V. Suleimanov Octavio Roncero

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 10-7 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.

Reaction dynamics

Transition state theory

10.1021/acs.jpclett.9b00555

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Citations (34)

Revisiting a Chemical Route to the Formation of CN⁻ in the Interstellar Medium

The Astrophysical Journal (2024)

Pablo del Mazo‐Sevillano M. Lara E. Yurtsever Mauro Satta Roland Wester

Abstract We discuss the HCN + H − reaction as a path to the formation of CN − , the smallest cyanopolyyne anion observed in several interstellar environments. We first obtain the new ab initio reactive potential energy surface using a full 5D representation, where only the C–N bond is kept fixed, and discuss the neural network procedure employed to yield an accurate fit for the dynamics. The reaction is then investigated by using a quasi-classical trajectory approach to scan the low-temperature range of the dark molecular clouds where the anion has been sighted. Calculations are extended to room temperature to make a successful comparison with existing experimental data. We further present reduced dimensionality modeling of the reaction as a 2D process within a variational-transition state treatment with the inclusion of long-range forces. The dominant role of such forces in producing large reaction rate coefficients is discussed for both treatments, which yield very similar sizes and behavior of such coefficients from 50 to 300 K. The implications of our results for the interstellar medium formation of the CN − species via this chemical route are discussed, suggesting its greater significance over the radiative electron attachment paths, whose rate coefficients were found by recent calculations to be orders of magnitude smaller.

Reaction rate

Reaction dynamics

10.3847/1538-4357/ad630c

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Citations (1)

Inelastic H H 3+ collision rates and their impact on the determination of the excitation temperature of H 3+

Astronomy and Astrophysics (2024)

Daniel Félix-González Pablo del Mazo‐Sevillano Alfredo Aguado Octavio Roncero J. Le Bourlot

In diffuse interstellar clouds, the excitation temperature derived from the lowest levels of mathrm H _3^+ is systematically lower than that derived from mathrm H _2. The differences may be attributed to the lack of state-specific formation and destruction rates of mathrm H _3^+, which are needed to thermalize the two species. In this work, we aim to investigate the possible influence of rotational excitation collisions of mathrm H _3^+ with atomic hydrogen on its excitation temperature. We used a time-independent close-coupling method to calculate the state-to-state rate coefficients, incorporating a very accurate and full-dimensional potential energy surface recently developed for H_4^+. We take a symmetric top approach to describe a frozen H_3^+ as an equilateral triangle. We derive rotational excitation collision rate coefficients of mathrm H _3^+ with atomic hydrogen in a temperature range corresponding to diffuse interstellar conditions up to $(J,K,±)= (7,6,+)$ and $(J,K,±) = (6,4,+)$ for its ortho and para forms. This allows us to obtain a consistent set of collisional excitation rate coefficients and to improve on a previous study that included speculations regarding these contributions. The new state-specific inelastic mathrm H H rate coefficients yield differences of up to $20,%$ in the excitation temperature, and their impact increases with decreasing molecular fraction. We also confirm the impact of chemical state-to-state destruction reactions on the excitation balance of H _3^+, and that reactive mathrm H H _3^+ collisions are also needed to account for possible further ortho to para transitions.

Collisional excitation

Excitation temperature

10.1051/0004-6361/202452977

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Citations (0)

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

The Journal of Chemical Physics (2023)

Pablo del Mazo‐Sevillano Jan Hermann

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 perspective.

Regularization

Energy functional

10.1063/5.0166432

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Citations (8)

Neural Network Potential Energy Surface for the low temperature Ring Polymer Molecular Dynamics of the H2CO + OH reaction

arXiv (Cornell University) (2021)

Pablo del Mazo‐Sevillano Alfredo Aguado Octavio Roncero

A new potential energy surface (PES) and dynamical study are presented of the reactive process between H2CO + OH towards the formation of HCO + H2O and HCOOH + H. In this work a source of spurious long range interactions in symmetry adapted neural network (NN) schemes is identified, what 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 networks scheme that prevents spurious asymptotic interactions. Quasi-classical trajectory 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 a 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 to excitations of the normal modes of the ring polymer.

Spurious relationship

Diabatic

Potential energy surface

Matrix (chemical analysis)

Source

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Citations (0)

Quantum study of the CH3+ photodissociation in full-dimensional neural network potential energy surfaces

The Journal of Chemical Physics (2024)

Pablo del Mazo‐Sevillano Alfredo Aguado J. R. Goicoechea Octavio Roncero

C H 3 + , a cornerstone intermediate in interstellar chemistry, has recently been detected for the first time by using the James Webb Space Telescope. The photodissociation of this ion is studied here. Accurate explicitly correlated multi-reference configuration interaction ab initio calculations are done, and full-dimensional potential energy surfaces are developed for the three lower electronic states, with a fundamental invariant neural network method. The photodissociation cross section is calculated using a full-dimensional quantum wave packet method in heliocentric Radau coordinates. The wave packet is represented in angular and radial grids, allowing us to reduce the number of points physically accessible, requiring to push up the spurious states appearing when evaluating the angular kinetic terms, through projection technique. The photodissociation spectra, when employed in astrochemical models to simulate the conditions of the Orion bar, result in a lesser destruction of CH3+ compared to that obtained when utilizing the recommended values in the kinetic database for astrochemistry.

Potential energy surface

Quantum number

Spurious relationship

10.1063/5.0206895

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Citations (0)

Zero- and High-Pressure Mechanisms in the Complex Forming Reactions of OH with Methanol and Formaldehyde at Low Temperatures

ACS Earth and Space Chemistry (2019)

Fedor Y. Naumkin Pablo del Mazo‐Sevillano Alfredo Aguado Yury V. Suleimanov Octavio Roncero

A recent ring polymer molecular dynamics study of the reactions of OH with methanol and formaldehyde at zero pressure and below 100 K has shown the formation of collision complexes with long lifetimes, longer than 100 ns for the lower temperatures studied, 20–100 K (del Mazo-Sevillano et al., 2019). These long lifetimes support the existence of multicollision events with the He buffer-gas atoms under experimental conditions, as suggested by several transition state theory studies of these reactions. In this work, we study these secondary collisions, as a dynamical approach to study pressure effects on these reactions. For this purpose, the potential energy surfaces of He with H2CO, OH, H2O, and HCO are calculated at highly accurate ab initio level. The stability of some of the complexes is studied using path integral molecular dynamics techniques, determining that OH–H2CO complexes can be formed up to 100 K or higher temperatures, whereas the weaker He–H2CO complexes dissociate at approximately 50 K. The predicted IR intensity spectra show new features which could help the identification of the OH–H2CO complex. Finally, the He–H2CO + OH and OH–H2CO + He collisions are studied using quasi-classical trajectories, finding that the cross section to produce HCO + H2O products increases with decreasing collision energy, and that it is ten times higher in the He–H2CO + OH case.

Transition state

Transition state theory

10.1021/acsearthspacechem.9b00051

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Citations (19)

Inelastic H + H^+_3 Collision rates and their impact in the determination of the excitation temperature of H^+_3

arXiv (Cornell University) (2024)

Daniel Félix-González Pablo del Mazo‐Sevillano Alfredo Aguado Octavio Roncero J. Le Bourlot

Context. In dffuse interstellar clouds the excitation temperature derived from the lowest levels of H+3 is systematically lower than that derived from H2. The differences may be attributed to the lack of state-specific formation and destruction rates of H+ 3 needed to thermalize the two species. Aims. In this work, we want to check the role of rotational excitation collisions of H+3 with atomic hydrogen on its excitation temperature. Methods. A time independent close-coupling method is used to calculate the state-to-state rate coefficients, using a very accurate and full dimensional potential energy surface recently developed for H+4. A symmetric top approach is used to describe a frozen H+3 as equilateral triangle. Results. Rotational excitation collision rate coefficients of H+3 with atomic Hydrogen have been derived in a temperature range appropriate to diffuse interstellar conditions up to (J; K; ?) = (7; 6; +) and (J; K; ?) = (6; 4; +) for its ortho and para forms. This allows to have a consistent set of collisional excitation rate coefficients and to improve the previous study where these contributions were speculated. Conclusions. The new state-specific inelastic H+3 + H rate coeffcients yield differences up to 20% in the excitation temperature, and their impact increases with decreasing molecular fraction. We also confirm the impact of chemical state-to-state destruction reactions in the excitation balance of H+3 , and that reactive H + H+3 collisions are also needed to account for possible further ortho to para transitions

10.48550/arxiv.2412.06697

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Citations (0)

MADWAVE3: a quantum time dependent wave packet code for nonadiabatic state-to-state reaction dynamics of triatomic systems

Computer Physics Communications (2024)

Octavio Roncero Pablo del Mazo‐Sevillano

Triatomic molecule

Code (set theory)

Dynamics

10.1016/j.cpc.2024.109471

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Citations (0)