arXiv subjects

Junwen Yin

Publications and source records attributed to Junwen Yin.

5 recordsLinked to original sources

arXiv2026

An Efficient On-the-Fly Nonadiabatic Coupling Framework Integrated into CP2K

Nonadiabatic molecular dynamics (NAMD) is widely used to describe hot electron relaxation and nonradiative recombination processes, but high computational costs limit its application to large supercells. Here, we implement a nonadiabatic coupling (NAC) module directly into CP2K, enabling on-the-fly NAC calculation during ab-initio molecular dynamics. Unlike conventional approaches relying on interfaces between external NAMD programs and electronic structure codes, this integration streamlines the workflow. Combined with CP2K's inherent Gaussian and Plane Waves (GPW) method, it achieves efficient NAC calculations for large-scale systems. To ensure numerical stability, a phase correction scheme is introduced to remove inconsistencies of wavefunction phases. Benchmark calculations of hot electron relaxation in crystalline pentacene agree with previous studies, while the results of simulations with and without phase correction show significant difference, confirming the necessity of the phase correction. Simulations on larger pentacene supercells further demonstrate the capability of this implementation for large-scale NAMD simulations.

physics.chem-ph↗

arXiv2025

Automatic generation of input files with optimised k-point meshes for Quantum Espresso self-consistent field single point total energy calculations

Performing density functional theory (DFT) calculations requires a careful choice of computational parameters to ensure convergence and obtain meaningful results. This represents a particularly important problem for high-throughput and agentic workflows, where due to computational cost, any additional convergence studies are preferably to be avoided. So, there is a need for tools and models which are able to predict DFT parameters from basic input information, such as a structure. In this work, we develop a machine learning approach to predict the appropriate k-point sampling in DFT calculations and generate the input files for Quantum Espresso self-consistent field calculations. To achieve this, we first generated a training dataset comprising over 20,000 materials, each with an energy convergence threshold of 1 meV/atom. Several ML models were evaluated for their ability to predict k-points distance, and uncertainty estimation was incorporated to guarantee that, for at least 85-95% of compounds, the predicted k-distance lies within the convergence region. The best-performing models are made publicly available through an open-access web application.

cond-mat.mtrl-sci↗

arXiv2025

Opposite impact of thermal expansion and phonon anharmonicity on the phonon-limited resistivity of elemental metals from first principles

Understanding electrical resistivity in metals remains a central challenge in quantifying charge transport at finite temperature. Current first-principles calculations based on the Boltzmann transport equation often match experiments, yet they almost always neglect the effect of thermal expansion and phonon anharmonicity. We show that both effects exert an opposite impact on electron-phonon coupling and on electrical resistivity. Thermal expansion enhances the coupling and leads to overestimation of resistivity, whereas anharmonic effects reduce it. By explicitly incorporating both effects, we establish a more complete description of resistivity in elemental metals, demonstrated here for Pb, Nb, and Al.

cond-mat.mtrl-sci↗

arXiv2025

Impact of anharmonicity on the carrier mobility of the Pb-free CsSnBr$_3$ perovskite

Charge carrier mobilities are critical parameters in halide perovskite solar cells, governing their average carrier velocity under an applied electric field and overall efficiency. Recent advances in first-principles calculations of electron-phonon interactions and carrier mobilities have enabled predictive computations for perovskite solar cells. However, the flexible octahedral frameworks and cationic displacements in these materials challenge the harmonic approximation, leading to significant difficulties in accurately calculating transport properties. To address these issues, we combine temperature-dependent effective potentials with the ab initio Boltzmann transport equations to compute carrier mobilities in a representative lead-free perovskite, CsSnBr$_3$. At room temperature, the electron/hole Hall mobilities in CsSnBr$_3$ are 106/256 cm$^2$/Vs when neglecting anharmonic effects and 59/145 cm$^2$/Vs when included. This overestimation of the harmonic approximation arises from the neglect of scattering coming from soft modes. We provide a workflow for performing first-principles carrier mobility calculations in anharmonic systems, advancing the predictive modeling of perovskite solar cells.

cond-mat.mtrl-sci↗

arXiv2022

The role of thermal fluctuations and vibrational entropy for the delta-to-alpha transition in hybrid organic-inorganic perovskites: the FAPbI3 case

FAPbI3, as a typical hybrid organic-inorganic perovskite, has attracted considerable interest due to its band gap suitable for visible light absorption and good thermal stability. A barrier to the use of FAPbI3 in commercial, stable devices is its unwanted black-to-yellow (non-perovskite to perovskite, commonly known as delta-to-alpha) phase transition at around 300 K. The intrinsic mechanisms of such phase transition are far from clear, being the detailed structural description for the alpha-phase still missing. By combined Density Functional Theory (DFT) calculations, lattice dynamics analysis and DFT molecular dynamics simulations, we assign the alpha-phase to the highly dynamic tetragonal phase, with the high-symmetry cubic structure emerging as a dynamically unstable maximum in the system potential energy landscape. We demonstrate computationally that the diffraction-observed cubic structure is the result of the averaging of different tetragonal distortions sampled in the experimental detection time scale as a result of the enhanced FA dynamics, instead of a static system of cubic symmetry. Further finite-temperature Gibbs free energy calculations confirm that the delta-to-alpha transition should be considered as a hexagonal-to-tetragonal transition in contrast to the previous hexagonal-to-cubic assignment. More importantly, the simulations indicate that the driving force of the process is the vibrational entropy difference rather than the rotational entropy as previously proposed. These results point out the dynamical nature of the alpha-phase, the importance of the overlooked tetragonal structure, and the key role of the vibrational entropy in perovskite-related phase transitions, the harnessing of which is critical for successful uptake of ABX3 hybrid organic-inorganic perovskites in commercial applications.

cond-mat.mtrl-sci↗