Pablo M. Piaggi, Michele Parrinello
We introduce a new fingerprint that allows distinguishing between liquid-like and solid-like atomic environments. This fingerprint is based on an approximate expression for the entropy projected on individual atoms. When combined with a local enthalpy, this fingerprint acquires an even finer resolution and it is capable of discriminating between different crystal structures.
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Fingerprints of Spin-Orbital Physics in Crystalline O$_2$
碱金属超氧化物KO $_2$是强关联系统的分子类似物，由轨道简并磁性O $_2^-$离子组成。利用第一性原理电子结构计算，我们建立了低能\textit{molecular}轨道的有效自旋-轨道模型，并认为KO $_2$的许多反常性质在不同的温度范围内复制了其轨道系统的状态.
Measuring similarities/dissimilarities between atomic structures is important for the exploration of potential energy landscapes. However, the cell vectors together with the coordinates of the atoms, which are generally used to describe periodic systems, are quantities not suitable as fingerprints to distinguish structures. Based on a characterization of the local environment of all atoms in a cell we introduce crystal fingerprints that can be calculated easily and allow to define configurational distances between crystalline structures that satisfy the mathematical properties of a metric. Thi…
By comparing photoemission spectroscopy with a non-perturbative dynamical mean field theory extension to many-body ab initio calculations, we show in the prominent case of pentacene crystals that an excellent agreement with experiment for the bandwidth, dispersion and lifetime of the hole carrier bands can be achieved in organic semiconductors provided that one properly accounts for the coupling to molecular vibrational modes and the presence of disorder. Our findings rationalize the growing experimental evidence that even the best band structure theories based on a many-body treatment of elec…
Vibrational, structural, and chemical fingerprints of ion diffusion in crystalline solids
针对直接MD模拟离子扩散计算成本高的问题，提出结合振动、结构指纹与MLIP化学嵌入的神经网络，用短轨迹预测离子自扩散系数，精度较高。
The vibrational entropy of a solid at finite temperature is investigated from the perspective of information theory. Ab initio molecular dynamics (AIMD) simulations generate ensembles of atomic configurations at finite temperature from which we obtain the $N$-body distribution of atomic displacements, $ρ_N$. We calculate the information-theoretic entropy from the expectation value of $\ln{ρ_N}$. At a first level of approximation, treating individual atomic displacements independently, our method may be applied using Debye-Waller B-factors, allowing diffraction experiments to obtain an upper bo…
High Entropy Alloys (HEAs) are designed by mixing multiple metallic species in nearly the same amount to obtain crystalline or amorphous materials with exceptional mechanical properties. Here we use molecular dynamics simulations to investigate the role of positional and compositional disorder in determining the low-frequency vibrational properties of CrMnFeCoNi HEAs. Our results show that the expected dependence of the density of states on the frequency as $D(ω)\simω^4$ is recovered for amorphous HEAs and is also observed for partially crystallized alloys with deviations that depend on the de…
Recently, machine learning has emerged as an alternative, powerful approach for predicting quantum-mechanical properties of molecules and solids. Here, using kernel ridge regression and atomic fingerprints representing local environments of atoms, we trained a machine-learning model on a crystalline silicon system in order to directly predict the atomic forces at a wide range of temperatures. Our idea is to construct a machine-learning model using a quantum-mechanical data set taken from canonical-ensemble simulations at a higher temperature, or an upper bound of the temperature range. With ou…
Photoresponse properties of single-crystalline thick film based on high-entropy topological insulator (Bi3/4Sb1/4)2(Te2/5Se2/5S1/5)3
该研究首次制备高熵拓扑绝缘体(Bi3/4Sb1/4)2(Te2/5Se2/5S1/5)3单晶厚膜，并展示其光电探测器在可见光下具有强光伏响应，响应度和探测率分别达8.7 mA/W和109 Jones。
B diffusion measurements are used to probe the basic nature of self-interstitial 'point' defects in Ge. We find two distinct self-interstitial forms - a simple one with low entropy and a complex one with entropy ~30 k at the migration saddle point. The latter dominates diffusion at high temperature. We propose that its structure is similar to that of an amorphous pocket - we name it a 'morph'. Computational modelling suggests that morphs exist in both self-interstitial and vacancy-like forms, and are crucial for diffusion and defect dynamics in Ge, Si and probably many other crystalline solids…
High-entropy alloys are made from random mixtures of principal elements on simple lattices, stabilized by a high mixing entropy. The recently discovered BCC Ta-Nb-Hf-Zr-Ti high entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials, e.g. it has a well defined superconducting transition along with an exceptional robustness against disorder. Here we show that the valence-electron count dependence of the superconducting transition temperature in the high entropy alloy falls between those of analogous simple solid solutions and …
We develop an irreversible thermodynamics framework for the description of creep deformation in crystalline solids by mechanisms that involve vacancy diffusion and lattice site generation and annihilation. The material undergoing the creep deformation is treated as a non-hydrostatically stressed multi-component solid medium with non-conserved lattice sites and inhomogeneities handled by employing gradient thermodynamics. Phase fields describe microstructure evolution which gives rise to redistribution of vacancy sinks and sources in the material during the creep process. We derive a general ex…
Mechanoluminescence in crystalline inorganic materials: local disorder and the elastic distortion hypothesis
本文通过弹性常数运动学分析，提出力致发光源于机械载荷下活性位点的动态畸变，并解释了静水压与剪切敏感性差异、卸载时发光峰等实验现象。
Specific heat study of single crystalline Pr$_{0.63}$ Ca$_{0.37}$ MnO$_{3}$ in presence of a magnetic field
本文报道了Pr $_{0.63}$ Ca $_{0.37}$ MnO $_3$单晶在0和8 T磁场作用下，在3 K-300 K温度范围内的比热研究结果。本文给出了磁场中一级电荷有序（CO）跃迁的熵和潜热的估计。CO跃迁的总熵变在0 T时为$\approx$ 1.8 J/mol K，在8 T磁场存在下降至$\sim$ 1.5 J/mol K。我们的测量使我们能够估计潜热$L_{CO}$ $\approx$ 235 J/mol参与CO转换。由于铁磁金属（FMM）态的熵与电荷有序绝缘（COI）态的熵相当，熵的细微变化使这两种状态中的任何一种稳定。我们的低温比热测量表明，线性项在0 T中不存在，并且令人惊讶的是，即使在金属FMM状态下也看不到。
We present a fingerprint-like method to analyze material defects after energetic particle irradiation by computing a rotation invariant descriptor vector for each atom of a given sample. For ordered solids this new method is easy to use, does not require extreme computational resources, and is largely independent of the sample material and sample temperature. As illustration we applied the method to molecular dynamics simulations of deuterated and pristine tungsten lattices at 300 K using a primary knock-on atom (PKA) of 1 keV with different velocity directions to emulate a neutron bombardment…
Raman Spectrometry, a Unique Tool to Analyze and Classify Ancient Ceramics and Glasses
拉曼显微/宏观光谱允许进行非破坏性的远程分析：可以识别坯体和釉、结晶和非晶相，包括着色釉的纳米颜料。最新一代的仪器是便携式的，允许在博物馆，现场等检查。本文概述了拉曼光谱技术分析古陶瓷和玻璃的潜力。研究了选定的玻璃以及各种瓷器，青瓷，彩陶和陶器的釉料，代表了古董，欧洲，地中海，伊斯兰和亚洲世界使用的不同生产技术。它们的鉴定是基于对结晶相和玻璃相的拉曼指纹的研究。拉曼参数允许作为组成和/或处理温度的函数的分类。特别注意的是给无定形和着色相（颜料）的光谱。
In this article, a theoretical description of the "ideal glass transition" is approached upon the adoption of a quaternion orientational order parameter. Unlike first-order phase transitions of liquids into crystalline solid states, glass transitions are entirely different phenomena that are non-equilibrium and that are highly dependent on the applied cooling rate. Herein, the "ideal glass transition" that occurs at the finite Kauzmann temperature at which point the configurational entropy of an undercooled liquid matches that of its crystalline counterpart is identified as a first-order quant…
We provide strong numerical evidence for a hidden multihyperuniform long-range order (MHLRO) in SiGeSn medium-entropy alloys (MEAs), in which the normalized infinite-wavelength composition fluctuations for all three atomic species are completely suppressed as in a perfect crystalline state. We show this MHLRO naturally leads to the emergence of short-range order (SRO) recently discovered in MEAs, which results in stable lower-energy states compared to alloy models with random or special quasi-random structures (SQSs) possessing no atomic SROs. The MHLRO MEAs approximately realize the Vegard's …
An anchoring transition at surfaces with grafted liquid-crystalline chain molecules
用计算机模拟和平均场方法研究了接枝液晶链分子表面上的液晶锚定。计算机模拟表明，集体倾斜链的溶胀层可能会导致非倾斜垂面（垂直）排列在流体中。结果可以在一个简单的理论模型中理解。相互吸引的链层上的锚定由链分子层和溶剂之间的界面结构决定。它由吸引链相互作用、溶剂的平移熵及其弹性之间的相互作用控制。预测了由接枝密度驱动的从倾斜取向到垂面取向的二级锚定转变。
Crystallization is a process of great practical relevance in which rare but crucial fluctuations lead to the formation of a solid phase starting from the liquid. Like in all first order first transitions there is an interplay between enthalpy and entropy. Based on this idea, to drive crystallization in molecular simulations, we introduce two collective variables, one enthalpic and the other entropic. Defined in this way, these collective variables do not prejudge the structure the system is going to crystallize into. We show the usefulness of this approach by studying the case of sodium and al…
Surface energies and surface elasticity largely affect the mechanical response of nanostructures as well as the physical phenomenon associated with surfaces such as evaporation and adsorption. Studying surface energies at finite temperatures is therefore of immense interest for nanoscale applications. However, calculating surface energies and derived quantities from atomistic ensembles is usually limited to zero temperature or involve cumbersome thermodynamic integration techniques at finite temperature. Here, we illustrate a technique to identify the energy and elastic properties of surfaces …
The transport properties at finite temperature of crystalline organic semiconductors are investigated, within the Su-Schrieffer-Heeger model, by combining exact diagonalization technique, Monte Carlo approaches, and maximum entropy method. The temperature-dependent mobility data measured in single crystals of rubrene are successfully reproduced: a crossover from super- to sub-diffusive motion occurs in the range $150 \leq T \leq 200$ K, where the mean free path becomes of the order of the lattice parameter and strong memory effects start to appear. We provide an effective model which can succe…
Cross slip of screw dislocations in crystalline solids is a stress-driven thermally activated process essential to many phenomena during plastic deformation, including dislocation pattern formation, strain hardening, and dynamic recovery. Molecular dynamics (MD) simulation has played an important role in determining the microscopic mechanisms of cross slip. However, due to its limited timescale, MD can only predict cross-slip rates in high-stress or high-temperature conditions. The transition state theory can predict the cross-slip rate over a broad range of stress and temperature conditions, …
X-ray absorption spectroscopy (XAS) is a premier technique for materials characterization, providing key information about the local chemical environment of the absorber atom. In this work, we develop a database of sulfur K-edge XAS spectra of crystalline and amorphous lithium thiophosphate materials based on the atomic structures reported in Chem. Mater., 34, 6702 (2022). The XAS database is based on simulations using the excited electron and core-hole pseudopotential approach implemented in the Vienna Ab initio Simulation Package. Our database contains 2681 S K-edge XAS spectra for 66 crysta…
High-entropy nanomaterials have been arousing considerable interest in recent years due to their huge composition space, unique microstructure, and adjustable properties. Previous studies focused mainly on high-entropy nanoparticles, while other high-entropy nanomaterials were rarely reported. Herein, we reported a new class of high-entropy nanomaterials, namely (Ta0.2Nb0.2Ti0.2W02Mo0.2)B2 high-entropy diboride (HEB-1) nanoflowers, for the first time. The formation possibility of HEB-1 was first theoretically analyzed from two aspects of lattice size difference and chemical reaction thermodyna…
Fingerprint of $T_c$ advancement in Li-doped Bi-2223 superconductors prepared by cationic molecular mixing within Pechini sol-gel synthesis
本研究通过Pechini溶胶-凝胶合成法制备Li掺杂Bi-2223超导体，发现5%Li掺杂样品具有最高临界温度111.4K，并揭示了量子磁通形成机制。
Establishing Coherent Momentum-Space Electronic States in Locally Ordered Materials
本研究以Bi$_2$Se$_3$为对象，利用角分辨光电子能谱发现即使在缺乏长程有序的非晶态中，局部有序的真实空间尺度也能产生相干的动量依赖电子态，揭示了电子相干性源于平均最近邻距离的倒数，为在更广泛材料中实现动量依赖量子现象开辟了新途径。
Quantum Computing of Phonon Spectra and Thermal Properties of Crystalline Solids
本文利用变分量子本征求解器和变分量子消去法，计算晶态硅和石墨的声子分支，验证了量子计算在热力学性质评估中的有效性。
Order evolution from a high-entropy matrix: understanding and predicting paths to low temperature equilibrium
本研究结合实验表征与模拟方法，揭示了高熵氧化物Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O中从高熵固溶体向低熵有序相演化的调控机制，建立了可预测高熵系统宏观态谱的框架，为性能工程设计提供支撑。
High-entropy alloys (HEAs) are solid solutions of multiple elements with equal atomic ratios which present an innovative pathway for de novo alloy engineering. While there exist extensive studies to ascertain the important structural aspects governing their mechanical behaviors, elucidating the underlying deformation mechanisms still remains a challenge. Using atomistic simulations, we probe the particle rearrangements in a yielding, model HEA system to understand the structural origin of its plasticity. We find the plastic deformation is initiated by irreversible topological fluctuations whic…
Computational Investigation of Reactivity Parameters, UV-Vis and IR Spectra, NLO Properties, and Temperature-Dependent Thermodynamic Characteristics of Schiff-Based Interdigitated 5O.m (m=14,16) Liquid Crystalline Compounds: A DFT Analysis
本研究通过DFT计算分析了5O.m（m=14,16）液晶的电子、光学及热力学性质，发现其低HOMO-LUMO能隙（4.17eV）赋予优异性能，并揭示了温度依赖的热力学特性以理解相变。
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