Agenda

Résumé : Modeling the properties of materials is a rapidly expanding area of research, as it becomes nowadays possible to conceive and design materials with specific properties, almost from scratch. Materials consist of an assembly of electrons and nuclei. Although much heavier than electrons, light nuclei, mainly hydrogen, exhibit quantization of the vibrational levels, zero-point energy and tunneling. These so-called Nuclear Quantum Effects (NQE) can have a large impact on the structure and the dynamics of materials [1]. NQE are also crucial for describing heavier nuclei at low temperatures and other phenomena, such as isotope effects, that escape a purely classical frame. In the last decade, in our group we have developed numerical models and theories that account for nuclear quantum effects, at various approximation levels [2,3,4]. I will briefly describe how we treat nuclei in a hybrid semi-classical regime [2,3], in the framework of the generalized Langevin equation. The behavior of systems that are at the borderline between the classical and quantum worlds is in general complex [4]. The genuine quantum characteristics might be spoiled by several physical factors, such as electric fields, high disorder, etc. I will illustrate through selected examples some paradoxical effects that can be encountered in condensed matter: ice [5,6], exotic phases of methane hydrates [7,8] at extreme pressures, typical of those inside giant icy planets of the solar system. I will conclude by discussing the importance of simulation methods that are able to account for the quantum dynamics of nuclei. The advent of machine-learning based techniques has opened the way to refine models for describing the inter-atomic forces, and the nuclear quantum effects, even if modest, might change the statistical properties appreciably. The explicit inclusion of NQE in simulations is a passionating and emerging field of research, with impact on many fields, spanning materials science, geophysics, theoretical physical chemistry and biochemistry.
[1] T. Markland and M. Ceriotti, Nuclear quantum effects enter the mainstream, Nature Rev. Chem. 2 (2018), 0109.
[2] E. Mangaud et al., The fluctuation–dissipation theorem as a diagnosis and cure for zero-point energy leakage in quantum thermal bath simulations, J. Chem. Theory Comput. 15 (2019) 2863;
[3] S Huppert, T Plé, S Bonella, P Depondt, F Finocchi, “Simulation of nuclear quantum effects in condensed matter via quantum baths”, Appl. Sci. 12 (2022) 4756.
[4] Thomas Plé, Simon Huppert, Fabio Finocchi, Philippe Depondt, Sara Bonella, “Anharmonic spectral features via trajectory-based quantum dynamics: a perturbative analysis of the interplay between dynamics and sampling”, J. Chem. Phys. 155 (2021) 22328.
[5] Y. Bronstein, P. Depondt, F. Finocchi, and A. M. Saitta, Quantum-driven phase transition in ice described via an efficient Langevin approach, Phys. Rev. B 89 (2014), 214101.
[6] Y. Bronstein, P. Depondt, F. Finocchi, et al., Quantum versus classical protons in pure and salty ice under pressure, Phys. Rev. B 93 (2016), 024104.
[7] S. Schaack et al., Observation of methane filled hexagonal ice stable up to 150 GPa, Proc. Natl. Acad. Sci. 116 (2019) 16204.
[8] S. Schaack, P. Depondt, M. Moog, F. Pietrucci, and F. Finocchi, How methane hydrate recovers at very high pressure the hexagonal ice structure, J. Chem. Phys. 152 (2020), 024504.
(All publications are freely available on HAL)