arXiv subjects

Iñigo Robredo-Magro

Publications and source records attributed to Iñigo Robredo-Magro.

3 recordsLinked to original sources

arXiv2026

Intrinsic switching leads to oxygen diffusion and breakdown in hafnia ferroelectrics

Conventional ferroelectrics exhibit well-defined polarization states linked through electric switching. In fluorite-structured ferroelectrics like hafnia, though, switching and oxygen diffusion seem to coexist, enriching the nature of ferroelectricity. Here we address the intrinsic, room-temperature switching and diffusion kinetics of hafnia ferroelectrics using machine-learning molecular dynamics. We identify two distinct switching mechanisms that are both active at realistic time scales. Critically, our simulations reveal that, because the lattice does not dissipate fast enough the heat originating from localized switching events, these two processes concatenate in an avalanche-like manner leading to oxygen conduction. Our results thus show that intrinsic switching leads to breakdown in hafnia ferroelectrics. They also suggest how this outcome might be avoided through suitably designed field pulses.

cond-mat.mtrl-sci↗

arXiv2026

Effective dynamic constants for nonequilibrium third-principles simulations

Computational studies of the thermodynamic properties of materials at the mesoscopic and macroscopic scales -- involving lengths and times of at least $μ$m and $μ$s, respectively -- rely on a coarse-graining approximation such that only a few relevant collective variables are treated explicitly. Those variables typically take the form of fields defined everywhere in space or macroscopic quantities when spatial inhomogeneities can be treated implicitly. The free energy is usually expressed as a Landau-like potential whose temperature-dependent minima track stable states, characteristic equilibrium fluctuations being implicitly accounted for. Further, the response of the system to external perturbations, and its relaxation toward thermal equilibrium, are described in terms of simple equations of motion governed by effective inertial and viscous-damping constants. There is considerable literature on the problem of deriving Landau free energy potentials, from either experiment or predictive atomistic simulations, including recent efforts to develop systematic machine-learning approaches that we denote ``third principles''. Much less attention has received the calculation of the effective constants controlling the nonequilibrium macroscopic or mesoscopic dynamics. Here we tackle that problem, describing a protocol that allows us to compute the temperature-dependent inertial and damping coefficients associated to the electric polarization in representative soft-mode ferroelectric PbTiO$_{3}$. Our scheme lends itself to a widespread application, although the non-trivial behaviors found in PbTiO$_{3}$ suggest that more case studies will be needed to finetune a general and robust calculation protocol. Our results also allow us to comment on common assumptions in the literature of effective dynamic treatments of ferroelectrics and related materials.

cond-mat.mtrl-sci↗

arXiv2025

Minimalist machine-learned interatomic potentials can predict complex structural behaviors accurately

The past decade has witnessed a spectacular development of machine-learned interatomic potentials (MLIPs), to the extent that they are already the approach of choice for most atomistic simulation studies not requiring an explicit treatment of electrons. Typical MLIP usage guidelines emphasize the need for exhaustive training sets and warn against applying the models to situations not considered in the corresponding training space. This restricts the scope of MLIPs to interpolative calculations, essentially denying the possibility of using them to discover new phenomena in a serendipitous way. While there are reasons to be cautious, here we adopt a more sanguine view and challenge the predictive power of two representative and widely available MLIP approaches. We work with minimalist training sets that rely on little prior knowledge of the investigated materials. We show that the resulting models -- for which we adopt modest/default choices of the defining hyperparameters -- are very successful in predicting non-trivial structural effects (competing polymorphs, energy barriers for structural transformations, occurrence of non-trivial topologies) in a way that is qualitatively and quasi-quantitatively correct. Our results thus suggest an expanded scope of modern MLIP approaches, evidencing that somewhat trivial -- and easy to compute -- models can be an effective tool for the discovery of novel and complex physical phenomena.

cond-mat.mtrl-sci↗