arXiv subjects

Pascal Raybaud

Publications and source records attributed to Pascal Raybaud.

4 recordsLinked to original sources

arXiv2025

Unbiased molecular dynamics for the direct determination of catalytic reaction times : paving the way beyond transition state theory

This study address the computational determination of catalytic reaction rates by moving beyond traditional Transition State Theory (TST), addressing its limitations in complex systems. The Hill relation framework, integrated with Adaptive Multilevel Splitting (AMS), offers exact rate constants for stochastic dynamics, overcoming TST's assumptions and limitations such as recrossings and post-transition state bifurcations. Two case studies validate the approach: water formation on {\gamma}-alumina and protonated isobutanol dehydration in the gas phase, demonstrating consistency with DFT results and highlighting the importance of dynamical effects. This framework provides a robust, computationally feasible methodology for studying complex catalytic processes.

physics.chem-ph↗

arXiv2023

Computing Surface Reaction Rates by Adaptive Multilevel Splitting Combined with Machine Learning and Ab Initio Molecular Dynamics

Computing accurate rate constants for catalytic events occurring at the surface of a given material represents a challenging task with multiple potential applications in chemistry. To address this question, we propose an approach based on a combination of the rare event sampling method called Adaptive Multilevel Splitting (AMS) and ab initio molecular dynamics (AIMD). The AMS method requires a one dimensional reaction coordinate to index the progress of the transition. Identifying a good reaction coordinate is difficult, especially for high dimensional problems such a those encountered in catalysis. We probe various approaches to build reaction coordinates such as Support Vector Machine and path collective variables. The AMS is implemented so as to communicate with a DFT-plane wave code. A relevant case study in catalysis: the change of conformation and the dissociation of a water molecule chemisorbed on the (100) $\gamma$-alumina surface is used to evaluate our approach. The calculated rate constants and transition mechanisms are discussed and compared to those obtained by a conventional static approach based on the Eyring-Polanyi equation with harmonic approximation. It is revealed that the AMS method may provide rate constants which are smaller than the static approach by up to two orders of magnitude due to entropic effects involved in the chemisorbed water.

physics.chem-ph↗

arXiv2018

Prediction of optimal catalysts for a given chemical reaction

We reveal a correlation between the M-X bond energy descriptor EMX for the optimal catalyst in a family of stoichiometry MiXj, and an intensive quantity defined as the standard enthalpy of the catalyzed reaction normalized to one mole of element X transferred by this reaction from reactants to products. M is a transition element, and the stoichiometry MiXj is fixed at the solid/fluid interface by the reaction conditions. We illustrate this for a relevant set of reactions involved in solar energy and industrial applications such as oxygen evolution, oxygen reduction and hydrogen evolution in electrolysis, hydrodesulfurization of thiophene, methanation of CO, hydrogenations of aromatics and alkenes, selective oxidation of methane, and ammonia synthesis and decomposition. We propose a quantitative model to explain this unexpected connection: this key finding and its interpretation should accelerate in silico discovery of catalysts.

cond-mat.mtrl-sci↗

arXiv2011

Free-energy profiles along reduction pathways of MoS2 M-edge and S-edge by dihydrogen: a first-principles study

We present the results of DFT calculations of free energy profiles along the reaction pathways starting from 50% coverage of MoS2 M-edge and 100% coverage of S-edge by sulfur, and leading to 37% coverage, i.e. creation of anionic vacancies, upon reduction by dihydrogen and production of H2S. Significant entropic and enthalpic corrections to electronic energies are deduced from the sets of normal modes vibration frequencies computed for all stationary and transition states. On that basis, we revisit and discuss the surface phase diagrams for M- and S- edges as a function of temperature, H2 partial pressure and H2S/H2 molar ratio, with respect to ranges of conditions relevant to industrial hydrotreating operations. We show that in such conditions, anionic vacancies on the M-edge, and surface SH groups on the M- and S- edges, may coexist at equilibrium. Moderate activation barriers connect stationary states along all paths explored.

physics.chem-ph↗