arXiv subjects

Wei-Zhe Yuan

Publications and source records attributed to Wei-Zhe Yuan.

3 recordsLinked to original sources

arXiv2026

Dynamic charges effect on infrared dielectric response of polar materials

Predictive modeling of the infrared dielectric function in polar materials is crucial for thermal management and infrared devices design. While the Green-Kubo molecular dynamics (MD) framework provides a nonperturbative route to compute dielectric responses from dipole fluctuations, yet it commonly relies on the fixed-charge approximation that neglects dynamic charge redistribution during atomic motion. Here, we employ a machine-learning neuroevolution potential with dynamic charges (qNEP) combined with Green-Kubo MD to investigate the dynamic charge effect on the infrared dielectric response of rutile TiO$_2$, a material with large Born effective charges (BEC). Our results show that dynamic charge effects become increasingly important at elevated temperatures and are essential for accurately predicting longitudinal optical phonon features and infrared reflectance. This work establishes that accurate prediction of infrared optical properties in polar materials under thermal excitation requires explicit treatment of dynamic charge evolution.

cond-mat.mtrl-sci↗

arXiv2025

Crystal Orientation Dependence of Extreme Near-Field Heat Transfer between Polar Materials Governed by Surface Phonon Modes

Due to the rapid development of micro- and nano-manufacturing and electronic devices, heat transfer at the transition regime between radiation and conduction becomes increasingly important. Recent work has demonstrated the importance of nonlocal optical response and phonon tunneling. However, it remains unclear how the crystal orientation impacts them. In this work, we study this effect on heat transport across vacuum gaps between magnesium oxide (MgO) by nonequilibrium molecular dynamics (NEMD) simulation. At 5~Å~gaps, the overall thermal conductance exhibits 30\% enhancement for [100] orientation versus [110] and [210], while becoming orientation-insensitive beyond 6~Å. When the gap size is extremely small, the crystal orientation significantly impacts the resonance frequencies of spectral thermal conductance which are quite close to those of unique surface phonon modes distinct from bulk counterparts. As the gap size gradually increases, the spectral thermal conductance gradually converges to the predicted results of fluctuation-electrodynamics (FE) theory in the long-wavelength approximation. Our findings reveal how surface phonon modes govern extreme near-field heat transfer across nanogap, providing insights for thermal management in electronic devices.

cond-mat.mes-hall↗

arXiv2025

Consistency between the Green-Kubo formula and Lorentz model for predicting the infrared dielectric function of polar materials

Accurate prediction of infrared dielectric functions in polar materials is fundamental for thermal and photonic applications, yet it remains unexplored whether the two main methods, Green-Kubo formula and Lorentz model, can give unified predictions. In this work, we present a detailed comparison of these two approaches using MgO and LiH as prototypical cases employing both empirical rigid ion model (RIM) and machine learning potential (MLP). We demonstrate that the conventional Lorentz model fails to capture the multi-phonon absorption inherent in Green-Kubo method, which can be resolved via using the phonon self-energy as a generalization of the usual linewidth. In addition, with RIM, a correction factor is required in the ionic contribution to infrared response to account for the electronic polarization effect, which is yet captured by MLP using the Born effective charges for calculating dipole moment. The present benchmark study thus enables cross-validation of dielectric function calculations while providing mechanistic insights into the polarization dynamics.

cond-mat.mes-hall↗