arXiv subjects

Owain T. Beynon

Publications and source records attributed to Owain T. Beynon.

3 recordsLinked to original sources

arXiv2026

An Exchange-Correlation Functional for Fast and Accurate Modeling of Ferroelectric Perovskites

We present a novel exchange correlation functional, C09x-PBEc, which combines C09 exchange with PBE correlation, to accurately model the ferroelectric properties of perovskites while retaining the computational efficiency of GGA functionals. With a growing interest in developing machine learning interatomic potentials (MLIPs) to model large-scale ferroelectric systems of technological relevance, it is important to scrutinise the density functional theory exchange-correlation functionals which are used to compute the forces, energies and stresses the MLIP is trained on. Using the example of the prototypical ferroelectrics lead titanate, PbTiO3, and barium titanate, BaTiO3 we show that many widely used functionals tend to overestimate their lattice constants and spontaneous polarization. Conversely, non-local van der Waals functionals with C09 exchange accurately capture these properties compared to experiment, but with a larger computational overhead than, for example, GGA. We show that C09x-PBEc combines the accuracy provided by the C09 exchange with the computational affordability of GGA, making it an excellent candidate to be used in the training of MLIPs for ferroelectric perovskites. We also demonstrate that an MLIP trained using C09x-PBEc accurately reproduces the ferroelectric-to-paraelectric phase transition temperature of PbTiO3 with respect to experiment, showing a marked improvement on MLIPs trained using GGA.

cond-mat.mtrl-sci↗

arXiv2026

Non-equilibrium Effects in Vibrational Modes Pumped by Inelastic Tunneling

The properties of strongly correlated electron materials exhibit a surprising sensitivity to small lattice distortions, providing an opportunity for their tuning by selective distortion driving, usually achieved by optical excitations. Using inelastic electron tunneling in scanning tunneling microscopy, we demonstrate that at the surface of a strongly correlated electron material, we can drive vibrational excitations out of equilibrium, by studying the dynamics of localized modes on the Pd-terminated surface of the delafossite oxide PdCrO2. This surface forms a tiling of hydrogen clusters of varying sizes and shapes upon hydrogen adsorption. Our findings reveal that vibrational excitations in the clusters exhibit longer lifetimes than on typical metal surfaces. Detailed analysis of the spectroscopy data reveals signatures of non-equilibrium effects in the excitations which we attribute to the extended lifetimes of these modes. Theoretical calculations support that the long-lived nature of the excitations is related to the unique properties of the substrate.

cond-mat.mtrl-sci↗

arXiv2026

Anharmonic Effects in Ge2Sb2Te5 and Consequences on Thermodynamic Stability

Chalcogenides are an important class of phase change material (PCMs) due to their application in digital memory solutions. Owing to their ability to reversibly cycle between crystalline and amorphous states, their use as phase change random access memory (PCRAM) is of interest, and of the many chalcogenide materials Ge2Sb2Te5 (GST) is a promising candidate owing to its stability and low crystallization temperature. GST possesses two stable crystalline polymorphs, cubic and hexagonal. Studies show that phenomena such as heat transport and thermal lattice expansion drive the phase-change nature of these materials. These phenomena are not incorporated in the harmonic approximation, which is a popular model for describing vibrations in solids. Through ab initio density functional theory (DFT), we computationally investigate the anharmonic behaviour of pristine hexagonal GST, i.e. without vacancies or defects, while considering the various stacking models that exist and inclusion of van der Waals (vdW) interactions in our modelling. We present the vibrational analysis of different stacking models in GST; Petrov and Kooi-De Hosson (KDH) models and the quantification anharmonic behaviour. Our calculations find that the KDH model is the most stable stacking sequence, being 88 meV more stable than the Petrov model when considering anharmonicity, where this difference is underestimated using a purely harmonic framework (65 meV). These results demonstrate the importance of incorporating anharmonic and dispersion effects when modelling GST, especially in the choice of stacking models, along with implications for phenomena relating to phase-change behaviour.

cond-mat.mtrl-sci↗