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Synthesizing Metastable Rocksalt-Type MgTe Based on High-Pressure Solid-State Phase Transition: A First-Principles Study
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The controllability;of pressure-induced structural transformation in the hexagonal wurtzite-type MgTe is studied by a first-principles pseudopotential method within the generalized gradient approximation (GGA). Based on the transitional mechanisms of the wurtzite→NiAs and the wurtzite→rocksalt, a special method of loading biaxial pressure on the (010) and (001) planes of an orthorhombic cell is designed. At equal biaxial pressure of 2. 75 GPa, an abrupt volume collapse is found and the WZ phase transforms into an orthorhombic phase with a tiny distortion. While the pressure decreases to zero, three lattice parameters a, b and c become equal and a metastable rocksalt-type MgTe is obtained. 相似文献
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Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations
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The pressure induced phase transitions of RuB2 from the OsB2-type structure to the ReB2-type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient ap- proximation for exchange and correlation. It is found that the phase transition occurs at 18.6 GPa. We predict the phase transition from the OsB2-type RuB2 to the ReB2-type RuB2 at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Grüneisen parameter on pressure and temperature for OsB2-type RuB2 and ReB2-type RuB2 are also investigated. 相似文献
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Pressure and Temperature Induced Phase Transition of ZnS from First-Principles Calculations
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The pressure induced phase transition of ZnS from the wurtzite (WZ) and the zincblende (ZB) structures to the rocksalt (RS) structure and the temperature induced phase transition from the ZB structure to the WZ structure are investigated by ab initio plane-wave pseudopotential density-functional theory (DFT), together with the quasiharmonic Debye model. It is found that the zero-temperature transition pressures from the WZ-ZnS and the ZB-ZnS to the RS-ZnS are 17.20 and 17.37 GPa, respectively. The zero-pressure transition temperature from the ZB-ZnS to the WZ-ZnS is 1199 K. All these results are consistent with the available experimental data. Moreover, the dependences of the normalized primitive cell volume V/V0 on pressure and thermal expansion coefficient α on temperature are also obtained successfully. 相似文献
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First-Principles Investigations of the Phase Transition and Optical Properties of Solid Oxygen
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Using density-functional-theory calculations, a monoclinic metallic post-ζ phase (space group C2/c) is predicted at 215 GPa. The calculated phonon dispersion curves suggest that this structure is stable at least up to 310 GPa. Oxygen remains a molecular crystal and there is no dissociation in the related pressure range. Moreover, it is found that the phase transition from ( to post-ζ phase is attributed to phonon softening, The significant change in the optical properties can be used to identify the phase transition. 相似文献
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A15 型 Nb3 Al 金属间化合物与 Nb3Sn 类似, 但其具有更好的应力应变容许特性和高场临界电流密度(J c ) . 由于 Nb3 Al 晶格原子排列的有序度较差, 其超导性能对晶格完整性不敏感, 且 Al 含量对 Nb3 Al 成相及 Tc有较大的影响. 因此对相结构的研究对 Nb3 Al 超导性及热学性质的影响具有理论和实际意义. 本文采取第一性原理以及热力学理论计算方法, 对 Nb3 Al 的结构进行晶格相结构转变、 原子位移以及热力学性质等系统计算研究. 结果发现晶格相结构转变的势垒高于原子的位移势垒, 且晶格相结构的转变温度高于 Nb3 Al 的熔化温度. 与 Nb 原子扩散位移相比,Al 原子具有更低的位移势垒, 且 Al 原子的“位移温度”低于熔化温度, 为1070 K. 对于 Nb 原子位移势垒, 通过统计方法得到 Nb 原子的“位移温度”为2333 K, 与实验中得到的 Nb3 Al 熔化温度2306 K 吻合较好,此计算结果表明高温下 Nb3 Al 的制备主要体现为 Al 原子的位移, 而 Nb 原子对该化合物的相结构稳定性具有更重要作用. 计算结论为更好地理解 Nb3 Al 制备过程中微观结构演化及扩散反应提供一定的理论依据. 相似文献
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Incomplete-Fusion-Fragmentation Model is used to analyze the multifragmentation of the projectile remnant in 600MeV/u Au+Au reaction.The theoretical resultsof the mass number,the excitation energy and the thermodynamical temperature of the projectile remnant agree well with experimental data.The backbending structure in the curve of temperature as a function of the excitation energy per nucleon,i.e. the evidence of liquid-gas phase transition,is reproduced and reasonably related to the decay modes phase transformation from dominance of the multifragmentation mode to the vaporization mode. 相似文献
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We have studied the structural, elastic, electronic properties, and pressure-induced phase transition of CuGaO2 by using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The obtained ground state properties of three phases were in agreement with previous works. The calculated enthalpy variations with pressure showed that the structural phase transition (β → 3R/2H) appeared at 65.5 ± 1 GPa. The changes in volume and band gap of β phase showed that there was a break between 30 and 40 GPa. The independent elastic constants of three phases were calculated. The 3R, 2H, and β phases were all mechanical stability and behaved in ductile manner under zero pressure. 相似文献
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运用无限纠缠投影对态(iPEPS)表示的张量网络(TN)算法,任意选取初态对二维无限正方格子XYX量子模型进行数值模拟演化,从而得到两个不同的具有简并对称破缺的基态波函数。在二维XYX量子模型中,既可以运用普适序参量的性质,又可以运用约化密度矩阵保真度的分叉行为,来确定这个系统由自发对称性破缺引起的量子相变的临界点及量子相变的类型。即基于iPEPS算法,从普适序参量和约化密度矩阵保真度的角度,来刻画二维XYX量子多体系统的相变,其为典型的Ising普适类的二级相变。因而,运用iPEPS算法通过普适序参量和约化密度矩阵保真度,可以确定一个量子系统经历的量子相变,这为研究热力学极限下的强关联电子量子系统的量子相变和量子临界现象提供了一种更有效的强大的工具。 相似文献
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Etienne Bertin Jean-Michel Billiot Rémy Drouilhet 《Journal of statistical physics》2004,114(1-2):79-100
In the present study we establish a phase transition in the nearest-neighbor continuum Potts model. The repulsion between particles of different type acts only on a nearest-neighbor graph, more precisely a subgraph of the Delaunay graph. This work is an adaptation of the Lebowitz and Lieb soft-core continuum Potts model. 相似文献
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An analytical investigation is made on two-dimensional traffic-flow model with alternative movement and exclude-volume effect between right and up arrows. Several exact results are obtained, including the upper critical density above which there are only jamming configurations, and the lower critical density below which there are only moving configurations. The observed jamming transition takes place at another critical density pc(N), which is in the intermediate region between the lower and upper critical densities. This transition is suggested to be a second-order phase transition, the order parameter is found. The nature of self-organization, ergodicity breaking and synchronization are discussed. Comparison with the sandpile model is made. 相似文献
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JINMeng CHENJi-Sheng LIJia-Rong 《理论物理通讯》2003,40(6):735-738
Starting from the QHD-I model, the nucleon-nucleon interaction potential in hot/dense nuclear matter is studied. We find that the attractive and repulsive Yukawa potential between nucleons is modified by the variation of Debye mass directly and, especially, the nucleon system described by this Yukawa potential will be unbounded at some critical T and μ. The critical point we get accords with that of L-G phase transition given by the P - ρs phase diagram. 相似文献
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A phenomenological model of the transition from quark-gluon phase to hadron phase is presented on the analogy of BCS theory. The massive current-quarks constitute the quark Cooper-pair, i.e., the hadron at Tc = 150~200 MeV, The order parameter of qq-pair takes a value in the range from 0.4 to 0.2 GeV. An experimental verification method of the present model in the heavy-ion collision is proposed. 相似文献
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Starting from the QHD-I model, the nucleon-nucleon interaction potential in hot/dense nuclear matter is studied. We find that the attractive and repulsive Yukawa potential between nucleons is modified by the variation of Debye mass directly and, especially, the nucleon system described by this Yukawa potential will be unbounded at some critical T and μ. The critical point we get accords with that of L-G phase transition given by the P - pB phase diagram. 相似文献
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Liu Ni Ling Ming-Xia Li Jun-Qi Liang J.-Q. 《International Journal of Theoretical Physics》2021,60(8):2812-2822
International Journal of Theoretical Physics - In this paper, we study Dicke phase transition from the normal phase to the superradiance phase and multiple stable states of T-C model by means of... 相似文献
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本工作将相互作用玻色子模型推广为包含f-和p-玻色子的情形。利用仿射型代数方法,通过对偶代数结构数值计算了多分量玻色型对力问题。利用对偶关系解析构建了与哈密顿量及其基底相联系的,由幺正的粒子数守恒和非粒子数守恒算符构成的准旋代数。在经该模型对106-116Cd偶偶核素实验能谱拟合的基础上,计算了基态和低激发态中各种玻色子占有率,准γ带中相邻能级摇摆等几个能特征该区域核素形状相变的序参量。从而展示了这些中重质量核从振动到γ-不稳定运动的形状相变行为。An extension of the original interacting boson model to the multi-level case including negative parity f-and p-bosons is made. An affinealgebraic approach is applied to solve the multi-level pairing problem numerically via the dual algebraic structure. The duality relation is explicitly used to construct the number-conserving unitary and number-nonconserving quasi-spin algebra, related with the Hamiltonian and the corresponding bases. After fitting to the experimental level energies of even-even 106-116Cd, several order parameters to signify the shape (phase) transition, such as occupation numbers of the bosons in the ground and a few lowest excited states, the level energy staggering in the (quasi)-γ band, are calculated to demonstrate the shape (phase) transitional behavior of these medium mass transitional nuclei. 相似文献
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First-Principles Calculations of Phase Transition and Stability of Si2CN4 under High Pressure
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A pressure-induced phase transition and stability in Si2 CN4 polymorphs under high pressure are studied by firstprinciples calculations. The result shows that the phase transition pressure of α- and β-Si2 CN4 to the cubic spinal phase is 29.9 GPa and 27.5 GPa predicted by thermodynamic method respectively. Under ambient condition, all of the three Si2CN4 polymorphs are metastable with positive formation enthalpy. Unlike the stability of Si3N4 polymorphs, α-Si2 CN4 is more stable than the β phase. 相似文献