Predicting the band gap of binary compounds from machine-learning regression methods

Density functional theory (DFT) is a ubiquitous first-principles method, but the approximate nature of the exchange-correlation functional poses an inherent limitation for the accuracy of various computed properties. In this context, surrogate models based on machine learning have the potential to provide a more efficient and physically meaningful understanding of electronic properties, such as the band gap. Here, we construct a gradient boosting regression (GBR) model for prediction of the band gap of binary compounds from simple physical descriptors, using a dataset of over 4000 DFT-computed band gaps. Out of 27 features, electronegativity, periodic group, and highest occupied energy level exhibit the highest importance score, consistent with the underlying physics of the electronic structure. We obtain a model accuracy of 0.81 and root mean squared error of 0.26 eV using the top five features, achieving accuracy comparable to previously reported values but employing less number of features. Our work presents a rapid and interpretable prediction model for solid-state band gap with high fidelity to DFT and can be extended beyond binary materials considered in this study.

Study on Enhancing the Thermoelectric Properties of Ti2CrSn Alloys

Based on the Hg2CuTi structure, the full-Heusler alloy Ti2CrSn, with a ground state band gap of semiconductor, is a thermoelectric material with potential applications. Through preparing Ti2CrSn1−xAlx (x = 0, 0.05, 0.1, 0.15, 0.2) series bulk materials via arc melting, the effects of the electrical and thermal transport properties of Ti2CrSn series alloys were investigated, and different Al doping on the phase structure, the microscopic morphology, and the thermoelectric properties of Ti2CrSn were examined. The results show that the materials all exhibit characteristics of p-type semiconductors at the temperature range of 323 to 923 K. Al elemental doping can significantly increase the Seebeck coefficient and reduce the thermal conductivity of the materials. Among them, the sample Ti2CrSn0.8Al0.2 obtained a maximum value of 5.03 × 10−3 for the thermoelectric optimal ZT value at 723 K, which is 3.6 times higher than that of Ti2CrSn.

Calculation of Nuclear Properties for 56–62Fe Isotopes in the Model Space (HO) Using NuShellX@MSU Code

The nuclear shell model has been applied to calculate the yrast energy levels, quadrupole transition probability (BE2), deformation parameter B2, rotational energy (hw), and inertia moment (20/h2) for the ground state band. The NuShellX@MSU code has been used to determine the nuclear properties of 56−62Fe isotopes, by using the harmonic oscillator (HO) model space for P (1f7/2), N (2p3/2), N (1f5/2), and N (2p1/2) orbits and (HO) interaction. The results are in good agreement with the available experimental data on the above nuclear properties and all nuclei under study. In addition, the back bending phenomenon has been explained by the calculations, and it has been very clear in 58,60,62Fe nuclei. It has also been confirmed and determined the most spins and parities of energy levels. In these calculations, new values have been theoretically determined for the most nuclear properties which were previously experimentally unknown.

The Highly Uniform Photoresponsivity from Visible to Near IR Light in Sb2Te3 Flakes

Broadband photosensors have been widely studied in various kinds of materials. Experimental results have revealed strong wavelength-dependent photoresponses in all previous reports. This limits the potential application of broadband photosensors. Therefore, finding a wavelength-insensitive photosensor is imperative in this application. Photocurrent measurements were performed in Sb2Te3 flakes at various wavelengths ranging from visible to near IR light. The measured photocurrent change was insensitive to wavelengths from 300 to 1000 nm. The observed wavelength response deviation was lower than that in all previous reports. Our results show that the corresponding energies of these photocurrent peaks are consistent with the energy difference of the density of state peaks between conduction and valence bands. This suggests that the observed photocurrent originates from these band structure peak transitions under light illumination. Contrary to the most common explanation that observed broadband photocurrent carrier is mainly from the surface state in low-dimensional materials, our experimental result suggests that bulk state band structure is the main source of the observed photocurrent and dominates the broadband photocurrent.

Partial alpha-decay half-life of 178Hfm2 isomer

A simple, semi-empirical, one-parameter calculation model based on the quantum mechanical tunneling mechanism through a potential barrier has been used to estimate the partial [Formula: see text]-decay half-life, [Formula: see text], of [Formula: see text] isomer. Alpha-transitions to levels of the ground-state band [Formula: see text] of [Formula: see text] have been considered, and the contributions to [Formula: see text] due to overlapping, Coulomb, and centrifugal barriers have been detailed in each case. Results have indicated a [Formula: see text]-value of [Formula: see text] and a predominance [Formula: see text] of [Formula: see text]-particles populating the level [Formula: see text], compatible with results by other authors. Besides, a single, universal-like formula to estimate half-life of alpha transitions, whatever [Formula: see text]-value and the characteristics of the parent nucleus (e-e, e-o, o-e and o-o nuclei, whether in the ground or isomeric states), has been envisaged.

Unusual Temperature Evolution of Quasiparticle Band Dispersion in Electron-Doped FeSe Films

The discovery of high-temperature (high-Tc) superconductivity in one-monolayer FeSe on SrTiO3 has attracted tremendous attention. Subsequent studies suggested the importance of cooperation between intra-FeSe-layer and interfacial interactions to enhance Tc. However, the nature of intra-FeSe-layer interactions, which would play a primary role in determining the pairing symmetry, remains unclear. Here we have performed high-resolution angle-resolved photoemission spectroscopy of one-monolayer and alkaline-metal-deposited multilayer FeSe films on SrTiO3, and determined the evolution of quasiparticle band dispersion across Tc. We found that the band dispersion in the superconducting state deviates from the Bogoliubov-quasiparticle dispersion expected from the normal-state band dispersion with a constant gap size. This suggests highly anisotropic pairing originating from small momentum transfer and/or mass renormalization due to electron–boson coupling. This band anomaly is interpreted in terms of the electronic interactions within the FeSe layers that may be related to the high-Tc superconductivity in electron-doped FeSe.