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On the existence of a second branch of transverse collective excitations in liquid metals 液态金属中横向集体激励第二分支的存在
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-08-11 DOI: 10.5488/CMP.26.33603
J. Wax, N. Jakse
It was found recently that the liquid dynamics of several metals (Li, Zn, Ni, Fe, Tl, Pb) under pressure is characterized by transverse spectral functions containing an additional high-frequency peak. To rationalize the pressure dependence of the contributions from different propagating processes to transverse spectral functions in liquid metals, ab initio molecular dynamics simulations were performed for two typical liquid metals (Na and Al) in a wide range of pressures. The influence of density/pressure is investigated for Na by considering four pressures ranging from 15 to 147 GPa, while the temperature influence is considered for Al between 600 K in the deep supercooled liquid up to 1700 K well above the melting point at ambient pressure. Both temperature and density dependence of the spectra of collective excitations are analyzed with a focus on the appearance of a second high-frequency mode in the transverse spectra. A correspondence between spectra of transverse collective excitations and the peak positions of the Fourier-spectra of velocity autocorrelation functions (vibrational density of states) is found.
最近发现,几种金属(Li, Zn, Ni, Fe, Tl, Pb)在压力下的液体动力学特征是包含一个附加高频峰的横向谱函数。为了合理解释不同传播过程对液态金属横谱函数的压力依赖性,对两种典型液态金属(Na和Al)在宽压力范围内进行了从头算分子动力学模拟。通过考虑从15到147 GPa的四种压力,研究了密度/压力对Na的影响,而考虑了深度过冷液体中600 K至1700 K远高于环境压力熔点的温度对Al的影响。分析了集体激发光谱的温度和密度依赖关系,重点讨论了横向光谱中第二高频模式的出现。发现了横向集体激励谱与速度自相关函数(态的振动密度)的傅立叶谱的峰值位置之间的对应关系。
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引用次数: 0
How should a small country respond to climate change? 一个小国应该如何应对气候变化?
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-08-11 DOI: 10.5488/cmp.26.33901
A. Haymet
Responses to the global climate crisis often focus on the largest current emitters of greenhouse gases. However, analysis shows that about a third of emissions come from a collection of small emitters, each contributing one- to two-percent of the total additional CO2 injected into the communal atmosphere. Attempts to hold global warming to less than 1.5℃ cannot succeed without also reducing emissions from these small countries.
对全球气候危机的反应往往集中在目前最大的温室气体排放国。然而,分析表明,大约三分之一的排放来自小型排放者的集合,每个排放者贡献了注入公共大气的额外二氧化碳总量的1%到2%。如果不减少这些小国的排放量,将全球变暖控制在1.5℃以内的努力是不可能成功的。
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引用次数: 0
An ab initio study of the static, dynamic and electronic properties of some liquid 5d transition metals near melting 一些液态5d过渡金属在熔点附近的静态、动态和电子性质的从头算研究
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-08-11 DOI: 10.5488/CMP.26.33601
D. González, L. González
We report a study on the static and dynamic properties of several liquid 5d transition metals at thermodynamic conditions near their respective melting points. This is performed by resorting to ab initio molecular dynamics simulations in the framework of the density functional theory. Results are presented for the static structure factors and pair distribution functions; moreover, the local short range order in the liquid metal is also analized. As for the dynamical properties, both single-particle and collective properties are evaluated. The dynamical structure shows the propagating density fluctuations, and the respective dispersion relation is obtained. Results are also obtained for the longitudinal and transverse current spectral functions along with the associated dispersion of collective excitations. For some metals, we found the existence of two branches of transverse collective excitations in the region around the main peak of the structure factor. Finally, several transport coefficients are also calculated.
本文报道了几种液态5d过渡金属在熔点附近的热力学条件下的静态和动态性质的研究。这是通过在密度泛函理论的框架内采用从头算分子动力学模拟来实现的。给出了静力结构因子和对分布函数的计算结果;此外,还分析了液态金属的局部短程阶数。至于动力学性质,单粒子和集体性质都得到了评价。动力学结构表现为传播的密度波动,并得到相应的色散关系。还得到了纵向和横向电流谱函数以及相关的集体激励色散的结果。对于某些金属,我们发现在结构因子主峰附近区域存在两个横向集体激励分支。最后,计算了几种输运系数。
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引用次数: 0
Proportional correlation between heat capacity and thermal expansion of atomic, molecular crystals and carbon nanostructures 原子、分子晶体和碳纳米结构的热膨胀与热容的比例关系
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-08-11 DOI: 10.5488/CMP.26.33602
M. Barabashko, A. I. Krivchikov, R. Basnukaeva, O. A. Korolyuk, A. Jeżowski
Correlation between thermal expansions β(T) and heat capacity C(T) of atomic and molecular crystals, amorphous materials with a structural disorder, carbon nanomaterials (fullerite C60, bundles SWCNTs of single-walled carbon nanotubes) was analyzed. The influence of the contribution to the coefficient of linear thermal expansion αXe(T) of Xe atoms adsorbed on the SWCNTs bundles is considered. The proportional correlation was found between the contribution to the coefficient of linear thermal expansion αXe(T) and the normalized to the gas constant heat capacity C Xe(T)/R of Xe atoms adsorbed on the SWCNTs bundles. The proportional correlation (β/β*) ∼ (CV/R) with the parameter β* for the bulk thermal expansion coefficient for cryocrystals is proposed. In the case of atomic crystals such as Xe and Ar, the proportional correlation (β/β*) ∼ (CV/R) is observed in the temperature range from the lowest experimental to temperatures where CV/R ≈ 2.3. The correlation is not observed in the temperatures where 2.3 < C V/R < 3 (classical Dulong-Petit law). It was found that the universal proportional correlation is also observed for molecular crystals with linear symmetry, such as CO2, CO, and N2O if the normalized heat capacity below the values CV/R ≈ 3 ÷ 3.5. It indicates that the proportional correlation between thermal expansions (β/β*) and heat capacity (CV/R) is related not only to the translational, but also to the rotational degrees of freedom of the molecule in the crystal. In the case of the C0, molecular crystal with translational and rotational degrees of freedom and intramolecular vibrations, the discussed above correlation occurs below the values of normalized heat capacity CV/R ≈ 7.5. In strongly anisotropic systems, such as systems of compacted bundles of single-walled carbon nanotubes and SWCNTs bundles with adsorbed Xe atoms, this universal dependence appears in a limited temperature range that does not include the lowest temperatures. A qualitative explanation of the observed correlation is proposed.
分析了原子晶体和分子晶体、结构无序的非晶态材料、碳纳米材料(富勒石C60、单壁碳纳米管束状SWCNTs)的热膨胀β(T)与热容C(T)的相关性。考虑了吸附在SWCNTs束上的Xe原子对线性热膨胀系数αXe(T)的贡献。发现对线性热膨胀系数αXe(T)的贡献与被吸附在SWCNTs束上的Xe原子对气体恒热容C Xe(T)/R的归一化呈正比关系。提出了晶体体热膨胀系数与参数β*之间的比例关系(β/β*) ~ (CV/R)。在原子晶体如Xe和Ar的情况下,在从最低实验温度到CV/R≈2.3的温度范围内观察到比例相关(β/β*) ~ (CV/R)。在2.3 < C V/R < 3(经典的Dulong-Petit定律)的温度下,没有观察到相关。当归一化热容小于CV/R≈3 ÷ 3.5时,对于线性对称的分子晶体,如CO2、CO和N2O,也存在普遍的比例相关关系。结果表明,晶体中分子的热膨胀(β/β*)与热容(CV/R)之间的正比关系不仅与分子的平移自由度有关,还与分子的旋转自由度有关。对于具有平移自由度和旋转自由度以及分子内振动的C0分子晶体,上述相关性发生在归一化热容CV/R≈7.5值以下。在强各向异性体系中,如单壁碳纳米管致密束体系和吸附Xe原子的SWCNTs束体系,这种普遍依赖关系出现在有限的温度范围内,不包括最低温度。对观察到的相关性提出了定性解释。
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引用次数: 0
Aspects of the microscopic structure of curcumin solutions with water-dimethylsulfoxide solvent. Molecular dynamics computer simulation study 姜黄素溶液的微观结构方面与水-二甲基亚砜溶剂。分子动力学计算机模拟研究
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-08-11 DOI: 10.5488/CMP.26.33605
T. Patsahan, O. Pizio
We explore some aspects of the microscopic structure of curcumin solutions with water-dimethylsulfoxide solvent of variable composition. Molecular dynamics computer simulations at isobaric-isothermal conditions are used for this purpose. The model consists of the OPLS-UA type model for the enol conformer of curcumin (J. Mol. Liq., 223, 707, 2016), the OPLS model for the dimethylsulfoxide (DMSO) and the SPC/E water model. Radial distributions for the centers of mass of curcumin molecules are evaluated and the corresponding running coordination numbers are analyzed. The disaggregation of curcumin clusters upon increasing the DMSO content in water-DMSO solvent is elucidated. Changes of the distribution of water and DMSO species around curcumin molecules are investigated. A qualitative comparison of our findings with the results of other authors is performed. A possibility to relate predictions of the model with the experimental observations in terms of the so-called critical water aggregation percentage is discussed.
我们探讨了姜黄素溶液的微观结构的一些方面与水二甲基亚砜的可变组成的溶剂。在等压等温条件下的分子动力学计算机模拟用于此目的。该模型包括姜黄素烯醇构象的OPLS- ua型模型(J. Mol. Liq., 223, 707, 2016)、二甲基亚砜(DMSO)的OPLS模型和SPC/E水模型。评价了姜黄素分子质心的径向分布,分析了相应的运行配位数。研究了姜黄素团簇在水-DMSO溶剂中随着DMSO含量的增加而发生的分解。研究了姜黄素分子周围水和DMSO的分布变化。我们的发现与其他作者的结果进行了定性比较。讨论了在所谓临界水聚集率方面将模型预测与实验观测联系起来的可能性。
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引用次数: 0
The fifty-year quest for universality in percolation theory in high dimensions 五十年来对高维渗流理论普适性的探索
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-06-23 DOI: 10.5488/CMP.26.33606
Tim Ellis, R. Kenna, B. Berche
Although well described by mean-field theory in the thermodynamic limit, scaling has long been puzzling for finite systems in high dimensions. This raised questions about the efficacy of the renormalization group and foundational concepts such as universality, finite-size scaling and hyperscaling, until recently believed not to be applicable above the upper critical dimension. Significant theoretical progress has been made resolving these issues, and tested in numerous simulational studies of spin models. This progress rests upon superlinearity of correlation length, a notion that for a long time encountered resistance but is now broadly accepted. Percolation theory brings added complications such as proliferation of interpenetrating clusters in apparent conflict with suggestions coming from random-graph asymptotics and a dearth of reliable simulational guidance. Here we report on recent theoretical progress in percolation theory in the renormalization group framework in high dimensions that accommodates superlinear correlation and renders most of the above concepts mutually compatible under different boundary conditions. Results from numerical simulations for free and periodic boundary conditions which differentiate between previously competing theories are also presented. Although still fragmentary, these Monte Carlo results support the new framework which restores the renormalization group and foundational concepts on which it rests.
虽然平均场理论在热力学极限下很好地描述了标度问题,但高维有限系统的标度问题一直是一个令人困惑的问题。这引起了对重整化群的有效性和基本概念的质疑,如普适性,有限尺寸缩放和超缩放,直到最近才被认为不适用于上临界维。解决这些问题已经取得了重大的理论进展,并在许多自旋模型的模拟研究中得到了验证。这一进展依赖于相关长度的超线性,这一概念在很长一段时间内遭到抵制,但现在已被广泛接受。渗透理论带来了额外的复杂性,例如相互渗透簇的扩散,这与来自随机图渐近性的建议明显冲突,并且缺乏可靠的模拟指导。本文报告了高维重整化群框架下渗流理论的最新进展,该框架支持超线性相关,并使上述大多数概念在不同边界条件下相互兼容。本文还介绍了自由边界条件和周期边界条件的数值模拟结果。虽然仍然不完整,这些蒙特卡罗结果支持恢复重整化群和它所依赖的基本概念的新框架。
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引用次数: 1
On the swelling properties of pom-pom polymers: impact of backbone length 绒球聚合物的溶胀性能:主链长度的影响
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-05-25 DOI: 10.5488/CMP.26.23301
K. Haydukivska, V. Blavatska
The present work continues our previous studies of pom-pom molecule [K. Haydukivska, O. Kalyuzhnyi, V. Blavatska, and J. Ilnytskyi, J. Mol. Liq. 328, 115456 (2021); Condens. Matter Phys. 25, 23302 (2022)]. The molecule consists of a linear backbone with two branching points at both ends, with functionalities f1 and f2. Here, the main attention is concentrated on studying the impact of the central backbone length on the configurational charactersitics of complex molecule, such as size and shape ratios. We apply both a direct polymer renormalization scheme based on continuous chain model and the alternative Wei's method to analyze a set of size and shape properties of pom-pom polymers in dilute solution. The size ratio of a pom-pom and a chain polymer of the same total molecular mass is calculated with an excluded volume interaction taken into account, and estimates for asphericity are found in Gaussian approximation, whereas for the size ratio we found a monotonous dependence of the length of backbone at different functionalities of side arms. Results for asphericity show a non-trivial behaviour.
本研究延续了我们以往对弹珠分子的研究[K]。张建军,张建军,张建军,等。中国生物医学工程学报,2003,19 (4):481 - 481;提供者。物质物理学报,25,23(2022)。该分子由两端有两个分支点的线性主链组成,官能团为f1和f2。在这里,主要关注的是研究中心骨架长度对复杂分子构型特征的影响,如大小和形状比。本文采用基于连续链模型的直接聚合物重整方案和替代的Wei方法,分析了稀溶液中软球聚合物的一组尺寸和形状特性。在考虑了排除的体积相互作用的情况下,计算了具有相同总分子质量的弹球和链状聚合物的尺寸比,并在高斯近似中发现了非球面性的估计,而对于尺寸比,我们发现了侧臂不同官能团的骨干长度的单调依赖。非球面的结果显示出非平凡的性质。
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引用次数: 1
Dirac fermion spectrum of the fractional quantum Hall states 分数量子霍尔态的狄拉克费米子谱
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-05-25 DOI: 10.5488/CMP.26.23703
I. N. Karnaukhov
Applying a unified approach, we study the integer quantum Hall effect (IQHE) and fractional quantum Hall effect (FQHE) in the Hofstadter model with short range interactions between fermions. An effective field, that takes into account the interaction between fermions, is determined by both amplitude and phase. Its amplitude is proportional to the interaction strength, the phase corresponds to the minimum energy. In fact, the problem is reduced to the Harper equation with two different scales: the first is a magnetic scale with the cell size corresponding to a unit quantum magnetic flux, the second scale determines the inhomogeneity of the effective field, forms the steady fine structure of the Hofstadter spectrum and leads to the realization of fractional quantum Hall states. In a sample of finite size with open boundary conditions, the fine structure of the Hofstadter spectrum consists of the Dirac branches of the fermion excitations and includes the fine structure of the edge chiral modes. The Chern numbers of the topological Hofstadter bands are conserved during the formation of their fine structure. The edge modes are formed into the Hofstadter bands. They connect the nearest-neighbor subbands and determine the conductance for the fractional filling.
采用统一的方法,研究了费米子之间短距离相互作用的Hofstadter模型中的整数量子霍尔效应(IQHE)和分数量子霍尔效应(FQHE)。考虑费米子之间相互作用的有效场是由振幅和相位共同决定的。其振幅与相互作用强度成正比,相位对应于最小能量。实际上,这个问题可以简化为两个不同尺度的Harper方程:第一个尺度是磁尺度,其胞体大小对应于一个单位量子磁通量,第二个尺度决定了有效场的非均匀性,形成了霍夫施塔特谱的稳定精细结构,导致分数阶量子霍尔态的实现。在开放边界条件下的有限尺寸样本中,霍夫施塔特谱的精细结构包括费米子激发的狄拉克分支和边缘手性模式的精细结构。拓扑霍夫施塔特带的陈恩数在其精细结构形成过程中是守恒的。边缘模形成霍夫施塔特带。它们连接最近邻子带并确定分数填充的电导。
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引用次数: 0
Random-anisotropy mixed-spin Ising on a triangular lattice 三角形晶格上的随机-各向异性混合自旋Ising
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-05-25 DOI: 10.5488/CMP.26.23601
E. S. de Santana, A. D. de Arruda, M. Godoy
We have studied the mixed spin-1/2 and 1 Ising ferrimagnetic system with a random anisotropy on a triangular lattice with three interpenetrating sublattices A, B, and C. The spins on the sublattices are represented by σA (states ±1/2), σB (states ±1/2), and SC (states ±1, 0). We have performed Monte Carlo simulations to obtain the phase diagram temperature kBT/|J| versus the strength of the random anisotropy D/|J|. The phase boundary between two ferrimagnetic FR1 and FR2 phases at lower temperatures are always first-order for p < 0.25 and second-order phase transition between the FR1, FR2 and the paramagnetic P phases. On the other hand, for values of p ⪆ 0.5, the phase diagram presents only second-order phase transition lines.
我们研究了具有随机各向异性的混合自旋-1/2和1 Ising铁磁系统,该系统在三角形晶格上具有三个互穿亚晶格a、B和c。亚晶格上的自旋分别用σA(态±1/2)、σB(态±1/2)和SC(态±1,0)表示。我们通过蒙特卡罗模拟得到了温度kBT/|J|随随机各向异性强度D/|J|的相图。在较低温度下,当p < 0.25时,两个铁磁FR1和FR2相之间的相界始终是一级相,FR1、FR2与顺磁p相之间的相界始终是二级相转变。另一方面,对于p⪆0.5的值,相图只显示二阶相变线。
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引用次数: 0
Pressure driven Weyl-topological insulator phase transition in Weyl semimetal SrSi2 Weyl半金属SrSi2中压力驱动的Weyl拓扑绝缘子相变
IF 0.6 4区 物理与天体物理 Q3 Physics and Astronomy Pub Date : 2023-05-25 DOI: 10.5488/CMP.26.23707
A. Shende, Shiv Kumar Gupta, Ashish Kore, Poorva Singh
Using DFT-based first-principles calculations, we demonstrate the tuning of the electronic structure of Weyl semimetal SrSi2 via external uniaxial strain. The uniaxial strain facilitates the opening of bandgap along Γ-X direction and subsequent band inversion between Si p and Sr d orbitals. Z2 invariants and surface states reveal conclusively that SrSi2 under uniaxial strain is a strong topological insulator. Hence, uniaxial strain drives the semimetallic SrSi2 into fully gapped topological insulating state depicting a semimetal to topological insulator phase transition. Our results highlight the suitability of uniaxial strain to gain control over the topological phase transitions and topological states in SrSi2.
利用基于dft的第一性原理计算,我们证明了通过外部单轴应变对Weyl半金属SrSi2的电子结构进行调谐。单轴应变有利于沿Γ-X方向的带隙打开和Si p和Sr d轨道间的能带反转。Z2不变量和表面态表明SrSi2在单轴应变下是一种强拓扑绝缘体。因此,单轴应变驱动半金属SrSi2进入完全间隙的拓扑绝缘状态,描绘了半金属到拓扑绝缘体的相变。我们的研究结果强调了单轴应变在SrSi2中控制拓扑相变和拓扑状态的适用性。
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引用次数: 0
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