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This paper reports for the first time an in-depth study based on first-principle calculations to unveil the underlying physics that governs the pressure induced structural phase transitions of Hg2Cl2 compound at room temperature. The phonon dispersion relations and phonon density of states have been critically explored for the tetragonal and orthorhombic phases of the compound to unveil the phonon modes associated with the phase transitions. The nature of the phase transition whether it is "displacive" or of "order–disorder" type has also been explored. We believe that the present study based on density functional theory and Born–Oppenheimer molecular dynamics calculations will help understand the underlying physics behind the above referred phase transitions and the anisotropic behavior of the compound, which in turn bears technologically significant relevance for its applications in optoelectronic devices, acousto-optic tunable filters, and in fiber-optic communication systems. [ABSTRACT FROM AUTHOR]

The paper is aimed to understand the key phonon modes that are responsible for the temperature dependent structural phase transition and negative thermal expansion of Hg2Cl2 compound for the first time with the aid of density functional theory and Born-Oppenheimer on the fly molecular dynamics calculations. The phonon dispersion spectra, phonon density of states and Grüneisen parameters for the body-centered tetragonal and base-centered orthorhombic phases of the compound have been explored in detail. The order parameter associated with the phase transition and its nature has also been reported herewith. We believe that the present study will not only help for futuristic designs of improved functionalized systems with Hg2Cl2 compound but also can augment their applications in thermoelectric conversion systems, fibre-optic communications, thermal expansion compensators and in fuel cells. [ABSTRACT FROM AUTHOR]

This work is motivated by the recent fabrication of a new four-atom-thick hexagonal polymorph from group IV monochalcogenide, so-called γ -GeSe (Lee et al 2021 Nano Lett. 21 4305). In this paper, we propose and examine the structural characteristics, electronic properties, and carrier mobility of monolayers Janus γ -Ge2 XY ( X / Y = S, Se, or Te) based on comprehensive first-principles calculations. Monolayers γ -Ge2 XY are confirmed to be structurally stable. Our calculations reveal that γ -Ge2 XY monolayers are indirect semiconductors with Mexican-hat-like dispersions in the top valence band. While the effect of the electric field on the energy band dispersions of γ -Ge2 XY monolayers is weak, the energy band dispersions are changed drastically in the presence of strain, especially compressive strain. Interestingly, a structural phase transition from semiconductor to metal is observed in γ -Ge2 XY under compressive strain. γ -Ge2STe and γ -Ge2SeTe possess high electron mobility with values of 3.22 × 10 3 and 8.33 × 10 3 cm2 V−1 s−1, respectively. Our findings not only explore the fundamental physical properties of γ -Ge2 XY but also open up new opportunities in the design of high-performance electronic nanodevices based on layered nanomaterials with Mexican-hat-like dispersions. [ABSTRACT FROM AUTHOR]

The recent development of high‐energy LiCoO2 (LCO) and progress in the material recycling technology have brought Co‐based materials under the limelight, although their capacity still suffers from structural instability at highly delithiated states. Thus, in this study, a secondary doping ion substitution method is proposed to improve the electrochemical reversibility of LCO materials for Li‐ion batteries. To overcome the instability of LCO at highly delithiated states, Na ions are utilized as functional dopants to exert the pillar effect at the Li sites. In addition, Fe‐ion substitution (secondary dopant) is performed to provide thermodynamically stable surroundings for the Na‐ion doping. Density functional theory calculations reveal that the formation energy for the Na‐doped LCO is significantly reduced in the presence of Fe ions. Na and Fe doping improve the capacity retention as well as the average voltage decay at a cutoff voltage of 4.5 V. Furthermore, structural analysis indicates that the improved cycling stability results from the suppressed irreversible phase transition in the Na‐ and Fe‐doped LCO. This paper highlights the fabrication of high‐energy Co‐rich materials for high voltage operations, via a novel ion substitution method, indicating a new avenue for the manufacturing of layered cathode materials with a long cycle life. [ABSTRACT FROM AUTHOR]

In this paper, a new version of the Stillinger–Weber (SW) potential for wurtzite GaN is presented, by which we systematically explore the structural and thermodynamical properties of native point defects and their complexes. In parallel, the semi-empirical Modified Embedded-Atom Method (MEAM) potential is selected for comparison. The SW and MEAM potentials are assessed by the reproduction of the fundamental properties of wurtzite GaN and by the ability to describe the inversion domain boundaries and the wurtzite–rocksalt phase transition. Then the structural search of native point defects and their complexes in GaN is implemented using both SW and MEAM potentials with the benchmark of Density Functional Theory (DFT) calculations. Besides vacancies and antisites, four N and five Ga interstitials are confirmed by refining the DFT calculations, among which two N split interstitials N + − N ⟨ 2 1 ̄ 1 ̄ 0 ⟩ and N + − Ga ⟨ 01 1 ̄ 0 ⟩ , and two Ga split interstitials, Ga + − Ga ⟨ 01 1 ̄ 0 ⟩ − g and Ga + − N ⟨ 01 1 ̄ 0 ⟩ , are observed for the first time. The SW potential correctly predicts the octahedral occupation GaOct to be the most stable Ga interstitial, while the MEAM potential predicts the ground state of the N + − N ⟨ 01 1 ̄ 0 ⟩ split interstitial ( N + − N ⟨ 01 1 ̄ 0 ⟩ − g) as the most stable N interstitial. However, neither of the two potentials could simultaneously generate the most stable configurations of N and Ga interstitials. The investigations of point defect complexes reveal that N octahedral Frenkel [FrenkelOct(N)] and paired antisite (NGaGaN) defects are unstable and get converted into V N ⊕ N + − N ⟨ 01 1 ̄ 0 ⟩ − g configurations with different separations between VN and N + − N ⟨ 01 1 ̄ 0 ⟩ − g point defects based on the DFT calculations. The formation energies calculated by the DFT and SW potential demonstrate that Schottky, Ga octahedral Frenkel [FrenkelOct(Ga)], and V N ⊕ N + − N ⟨ 01 1 ̄ 0 ⟩ − g point defect complexes are energetically feasible and that they should not dissociate into two isolated point defects. In contrast, the MEAM potential predicts the dissociation to be exothermic for Schottky and V N ⊕ N + − N ⟨ 01 1 ̄ 0 ⟩ − g. Overall, the structural features concerned with N–N or Ga–Ga bonds relaxed by the SW potential are more consistent with DFT calculations than the MEAM counterpart. [ABSTRACT FROM AUTHOR]

Iron phosphate materials have attracted a lot of attention due to their potential as cathode materials for lithium-ion rechargeable batteries. It has been shown that lithium insertion or extraction depends on the Fe mixed valence and reduction or oxidation of the Fe ions' valences. In this paper, we report a new synthesis method for the Fe3(PO3OH)4(H2O)4 mixed valence iron phosphate. In addition, we perform temperature-dependent measurements of structural and physical properties in order to obtain an understanding of electronic–structural interplay in this compound. Scanning electron microscope images show needle-like single crystals of 50 μm to 200 μm length which are stable up to approximately 200 °C, as revealed by thermogravimetric analysis. The crystal structure of Fe3(PO3OH)4(H2O)4 single crystals has been determined in the temperature range of 90 K to 470 K. A monoclinic isostructural phase transition was found at ~213 K, with unit cell volume doubling in the low temperature phase. While the local environment of the Fe2+ ions does not change significantly across the structural phase transition, small antiphase rotations occur for the Fe3+ octahedra, implying some kind of electronic order. These results are corroborated by first principle calculations within density functional theory, which also point to ordering of the electronic degrees of freedom across the transition. The structural phase transition is confirmed by specific heat measurements. Moreover, hints of 3D antiferromagnetic ordering appear below ~11 K in the magnetic susceptibility measurements. Room temperature visible light absorption is consistent with the Fe2+/Fe3+ mixed valence. [ABSTRACT FROM AUTHOR]

In this paper, the first‐principles calculations based on the Density Functional Theory (DFT) have been used to study the effect of strain on the structural, electronic, optical and thermoelectric properties of the puckered Si2SeS monolayer. Our calculations show that the puckered Si2SeS monolayer has an indirect band gap of 1.30 eV at the equilibrium state, which can be tuned by biaxial strain and the semiconductor–metal phase transition occurs at −10%. Interestingly, a high absorption coefficient exceeds 107 cm−1 in the visible light region under compression biaxial strain was predicted. The electronic Figure of merit (ZTe) of puckered Si2SeS monolayer reaches 2.55 under the tensile biaxial strain of +6%. The presented results show the promising potential of puckered Si2SeS monolayer for optoelectronic and energy conversion applications. [ABSTRACT FROM AUTHOR]

The phase-field crystal (PFC) method is known as a relatively new continuum approach for describing the microstructural dynamics of materials during structural and phase transitions. In contrast to molecular dynamics (MD) or density functional theory (DFT) methods, PFC allows description processes on diffusion time scales while maintaining an atomistic spatial resolution which explains its attraction to scientists over the last 20 years. After certain development, PFC serves today as a solution of a wide variety of new and increasingly complex problems. As a result, dozens of various modifications of the original PFC model are already helping to study special features in material science. New possibilities and challenges arise when extended spatio-temporal correlations are introduced in PFC model. The current paper briefly systematizes and characterizes PFC model's applications mainly focused on spatio-temporal correlations, systems with memory and models suitable for the description of non-equilibrium phase transformations. [ABSTRACT FROM AUTHOR]

This paper shows how terahertz light can drive ultrafast topological phase transitions in monolayer transition metal dichalcogenides (TMDs). The phase transition is induced by the light interaction with both electron and phonon subsystems in the material. The mechanism of such a phase transition is formulated by thermodynamics theory: the Gibbs free energy landscape can be effectively modulated under light, and the relative stability between different (meta‐)stable phases can be switched. This mechanism is applied to TMDs and reversible phase transitions between the topologically trivial 2H and nontrivial 1T′ phases are predicted, providing appropriate light frequency, polarization, and intensity are applied. The large energy barrier on the martensitic transformation path can be significantly reduced, yielding a small energy barrier phase transition with fast kinetics. Compared with other phase transition schemes, light illumination has great advantages, such as its non‐contact nature and easy tunability. The reversible topological phase transition can be applicable in high‐resolution fast data storage and in‐memory computing devices. [ABSTRACT FROM AUTHOR]

In this paper, we study the structural, electronic, magnetic, mechanical and thermal properties of Half-Heusler CoMnTe, using the Density Functional Theory (DFT) with the generalized gradient approximation (GGA) and GGA plus the Hubbard correction (GGA+U). The obtained results show that the compound is more stable in γ -phase with the ferromagnetic (FM) configuration than the nonmagnetic (NM) among the three considered structural phases (α , β , γ) and there is no possibility of martensitic transformation under the tetragonal distortion effect. The computed total magnetic moments of CoMnTe by GGA and GGA+U are 4 μ B and 4.13 μ B , respectively, arising mainly from the Mn atom. The obtained density of states and band structures using GGA approach show that the compound exhibits half-metallic behavior with 100% spin polarization. As the Hubbard is added, the electronic properties show an electronic phase transition from half-metallic to metallic behavior with 68% spin polarization. While the thermal and mechanical properties show very small changes, confirming that the studied compound is mechanically and dynamically stable. • CoMnTe compound is more stable in γ -phase with the ferromagnetic configuration. • CoMnTe compound is mechanically and thermodynamically stable. • CoMnTe compound is promising for spintronic applications. [ABSTRACT FROM AUTHOR]

The structural, elastic and electronic properties of XCoSb along with the impact of pressure on the structure of the compounds are discussed in this paper. Calculations have been carried out using the pseudopotential plane wave method within generalized gradient approximation according to the Perdew-Burke-Ernzerhof (GGA-PBE) method. At ambient conditions, XCoSb crystallizes in a C1b-type cubic structure and we observed that at high-pressure VCoSb, CrCoSb and MnCoSb undergo a phase transition from cubic to the LiGaGe-type hexagonal structure. Elastic constants are reported for the first time. The electronic band structure and density of states (DOS) show that ScCoSb and TiCoSb are semiconductors and non-magnetic while VCoSb, CrCoSb and MnCoSb are half-metallic ferromagnetic. In addition, we have also calculated elastic moduli, Zener anisotropic factor, Poisson's ratio and transverse and longitudinal sound velocities from the second-order elastic constant. [ABSTRACT FROM AUTHOR]

In this paper, the non-local density functional theory is used in combination with SAFT-VR, to investigate the pore pressure behaviour of water confined in various nanopores. Due to the efficiency and low computational cost of the method, many configurations and thermodynamic conditions are explored. In particular, capillary condensation and evaporation of water, their impact on the pore pressure, and the effect of surface activation are evaluated. Successive first-order phase transitions of ultra-confined water monolayer are also highlighted. [ABSTRACT FROM AUTHOR]

Layered perovskite-like oxide K 2 La 2 Ti 3 O 10 is a perspective photocatalyst for water decomposition at ultraviolet irradiation. In this paper using a density functional theory approach electronic structures of dehydrated and hydrated phases of K 2 La 2 Ti 3 O 10 have been studied. It has been found that the water induced phase transformation from I 4/ mmm to P 4/ mmm occurs in two steps: at first an increase in the distance between the perovskite layers prevails, and then a shift of the perovskite layers occurs with a moderate changing of the interlayer distance. The band structure calculations have done using the modified Becke-Johnson potential show that K 2 La 2 Ti 3 O 10 exhibits indirect band gap of about 3.1 eV. The valence band maximum potential is located at 2.23 eV (vs. normal hydrogen electrode), while the conduction band minimum potential is at −0.91 eV. This confirms the ability of K 2 La 2 Ti 3 O 10 both for photocatalytic oxidation of water (producing dioxygen and protons) or pollutants, and to reduce H+ to H 2. However, the transfer rate, estimated implicitly from the ratio of the effective masses of the photogenerated holes and electrons in valence and conduction bands, limits photocatalytic performance of K 2 La 2 Ti 3 O 10 due to separation ineffectiveness of charge carriers. • Both LDA and GGA fail to describe correctly band gap in K 2 La 2 Ti 3 O 10. • The mBJ potential gives an indirect band gap of about 3.1 eV in K 2 La 2 Ti 3 O 10. • Photocatalytic properties of K 2 La 2 Ti 3 O 10 for water splitting was studied. • Low transfer rate limits photocatalytic performance of pristine K 2 La 2 Ti 3 O 10. • Water induced phase transition in K 2 La 2 Ti 3 O 10 from I 4/ mmm to P 4/ mmm was modelled. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Samples of different mol% of copper doped titania were studied. • At 650 °C, samples with 0% and 2% Cu were comprised of 100% rutile. • 4% and 8% Cu doping the samples showed 27.3% and 74.3% anatase respectively. • DFT studies of show formation of oxygen vacancies and a 2+ oxidation state for Cu. Abstract This paper shows that incorporation of Cu inhibits the anatase to rutile phase transition at temperatures above 500 °C. The control sample, with 0% Cu contained 34.3% anatase at 600 °C and transitioned to 100% rutile by 650 °C. All copper doped samples maintained 100% anatase up to 600 °C. With 2% Cu doping, anatase fully transformed to rutile at 650 °C, at higher Cu contents of 4% & 8% mixed phased samples, with 27.3% anatase and 74.3% anatase respectively, are present at 650 °C. All samples had fully transformed to rutile by 700 °C. 0%, 4% and 8% Cu were evaluated for photocatalytic degradation of 1, 4 dioxane. Without any catalyst, 15.8% of the 1,4 dioxane degraded upon irradiation with light for 4 h. Cu doped TiO 2 shows poor photocatalytic degradation ability compared to the control samples. Density functional theory (DFT) studies of Cu-doped rutile and anatase show formation of charge compensating oxygen vacancies and a Cu2+ oxidation state. Reduction of Cu2+ to Cu+ and Ti4+ to Ti3+ was detected by XPS after being calcined to 650–700 °C. This reduction was also shown in DFT studies. Cu 3d states are present in the valence to conduction band energy gap upon doping. We suggest that the poor photocatalytic activity of Cu-doped TiO 2 , despite the high anatase content, arises from the charge recombination at defect sites that result from incorporation of copper into TiO 2. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a new interionic potential is derived for silver iodide (AgI) via the Chen-Möbius lattice inversion and ab initio calculation. The accuracy of the proposed potential is checked by comparing the molecular dynamics simulation results on the static properties, structural stability, disordered states, mean-squared displacement and phase transition of AgI with experimental data. The simulation results are consistent with experimental data and density functional theory (DFT) calculations, indicating that the proposed interionic potential is valid over a wide range of interionic separations and applicable for describing the major properties of AgI. Highlights • We derive a new interionic potential for AgI via the Chen-Möbius lattice inversion and DFT calculations. • The accuracy of the proposed potential is checked by comparing the MD simulation results with experimental and DFT data. • The potential developed in this work is more favorable in describing several properties than former potential. [ABSTRACT FROM AUTHOR]

The classical Oseen-Frank theory of liquid crystal elasticity is based on the experimentally verified fact that there are three independent modes of distortion, each with its associated elastic constant. On the other hand, the arguably more first-principles order parameter-based Landau-de Gennes theory only involves two independent elastic modes. The resulting ‘elastic constants problem’ has led to a considerable amount of vexation among theorists. In a series of papers at the turn of the century, Fukuda en Yokoyama suggested that the resolution of this problem could be found in the proper treatment of non-local effects in the ideal part of the free energy. They used an ingenious, but technically complex, technique based on a field-theoretic approach to semi-flexible polymers. Here we revisit their idea but now in the more accessible framework of density functional theory of rigid particles. Our work recovers their main results for rod-like particles, in that generically an ordered assembly of non-interacting rods has three independent elastic constants associated to it that all scale as the square of the length of the particles and obey the inequalities . We also consider the case of disc-like particles, and then find in line with expectations that . [ABSTRACT FROM AUTHOR]

Uranium hydride is a novel hydrogen-rich system which contains 5 f electrons. Uranium hydride can not only be used in the nuclear fuel industry, but also be a candidate of high superconducting-temperature materials. In this paper, we have searched the stable uranium hydride structures by using particle swarm optimization method and first-principles calculations. Besides UH 8 and UH 9 , we find that UH 17 , which contains larger hydrogen content than most hydride materials reported before, is also stable at high pressure. The atomic structures, electronic structures and phase diagram of uranium hydrides are provided, and we find that all of the discovered uranium hydrides are metals with negligible magnetic moments. [ABSTRACT FROM AUTHOR]

Recently following the success of the density functional theory (DFT) in obtaining the structure and thermodynamics of homogeneous and inhomogeneous classical systems such as simple fluids, dipolar fluid and binary hard spheres, this theory was also applied to obtain the density profile of a molecular fluid in between hard planar walls by Kalpaxis and Rickayzen. In the theory of molecular fluids, the direct correlation function (DCF) can be used to calculate the equation of state, free energy, phase transition, elastic constants, etc. It is well known that the hard core molecular models play an important role in understanding complex liquids such as liquid crystals. In this paper, a classical fluid of nonspherical molecules is studied. The required homogeneous (DCF) is obtained by solving Orenstein-Zernike (OZ) integral equation numerically. Some of the molecules in the liquid crystals have a sphere shape and this kind of molecular fluid is considered here. The DCF sphere of the molecular fluid is calculated and it will be shown that the results are in good agreement with the pervious works and the results of computer simulation. Finally the electro-optical properties of ellipsoid liquid crystal using DCF of these molecules are calculated. [ABSTRACT FROM AUTHOR]

The phase transition performance of the CaCl2 · 6H2O-Ca(NO3)2 · 4H2O composite salt system with nucleating and thickening agents was investigated in this paper. The CaCl2 · 6H2O-Ca(NO3)2 · 4H2O composite salt system was prepared by adding Ca(NO3)2 · 4H2O (12 wt%) to CaCl2 · 6H2O. Different nucleating agents including SrCl2 · 6H2O, SrCO3, BaCl2, BaCO3, Na2B4O7 · 10H2O, H3BO3 and NH4Cl were used to address the problems of phase segregation and supercooling phenomena during the phase change process. The results show that the single nucleating agent SrCl2 · 6H2O or the mixture of nucleating agents with 2 wt% SrCl2 · 6H2O, 1 wt% BaCl2 and 0.5 wt% of thickening agent carboxyl methyl cellulose is the most suitable for this system. The latent heat remained constant at about 116 J/g before and after adding the agents. Density functional theory was used to further investigate the microstructure-related reason for the salt-water separation and supercooling phenomena. It can be deduced that the hydrogen bond is the vital factor involved during the phase transition. The aim of adding thickener was to form more hydrogen bonds which encapsulated the hydrated species and made it difficult to lose the hydrated waters. The main purpose of adding nucleating agent was to break the metastable state among microscopic species. The results of this work indicate that the CaCl2 · 6H2O-Ca(NO3)2 · 4H2O salt mixture has potential as a thermal energy storage material. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The 1T phase of transition metal dichalcogenides (TMDs) is predicted to be an excellent anode material of lithium batteries (LIBs) by many previous theoretical investigations, especially in Mo- and W-TMDs, mainly because of its metallic character. However, the Peierls instability will induce a spontaneous transition from 1T to 1T′ phase, which was ignored by previous studies but should play an important role during the cycling process of LIBs. In this paper, the density functional theory calculations were adopted to systematically studied Li diffusion behavior on the different variants of low symmetry 1T′-MoS 2. It was revealed that the diffusion barrier parallel to the Mo-Mo dimerization zigzag chain is almost two times to the perpendicular direction. Besides, the diffusion direction will be turned to ∼120° after Li crosses the domain boundary in a 1T′ multi-domain nanosheet. Similar results could also be observed in Na and K diffusion. Our finding not only revealed the Li (Na or K) diffusion behavior of 1T′-MoS 2 but also propose to control the atom diffusion direction through strain engineering, which may inspire the further development of electronic devices. [Display omitted] • The structural anisotropy of 1T′-MoS 2 will lead to Li diffusion anisotropy. • The diffusion barrier along the Mo-Mo dimerization zig-zag chain is two times than that along the perpendicular direction. • The diffusion direction of Li atoms would be changed in different variants. • Local strain could be applied to control the local variant in a multi-domain nanosheet and then modulate the diffusion direction. [ABSTRACT FROM AUTHOR]

The contents of issues 3 and 4 of Structural Chemistry from the calendar year 2015 are summarized in the present review. A brief thermochemical commentary and possible guidelines for future research are added to the summary of each paper. [ABSTRACT FROM AUTHOR]

The IrTe transition metal dichalcogenide undergoes a series of structural and electronic phase transitions when doped with Pt. The nature of each phase and the mechanism of the phase transitions have attracted much attention. In this paper, we report scanning tunneling microscopy and spectroscopy studies of Pt-doped IrTe with varied Pt contents. In pure IrTe, we find that the ground state has a 1/6 superstructure, and the electronic structure is inconsistent with Fermi surface nesting-induced charge density wave order. Upon Pt doping, the crystal structure changes to a 1/5 superstructure and then to a quasi-periodic hexagonal phase. First-principles calculations show that the superstructures and electronic structures are determined by the global chemical strain and local impurity states that can be tuned systematically by Pt doping. [ABSTRACT FROM AUTHOR]

The contents of issues 1 and 2 for the calendar year 2014 are summarized in the current review of the journal Structural Chemistry. A brief thermochemical commentary is added to the summary of each paper. [ABSTRACT FROM AUTHOR]

Zn-doped PbTiO3has been developed to derive mechanical properties and phase transition. In this paper, a Zn atom 0–16% wt which occupied PbTiO3structure was investigated by using first principles density functional theory. The generalized gradient approximation was employed to determine the exchange correlation potential. The findings revealed that Zn-doped PbTiO3, calculated through Mulliken population analysis, had atomic (both ionic and covalent) bonding. In addition, the elastic constant satisfied the traditional mechanical stability conditions. Bulk modulus, Young's Modulus and Poisson's Ratio were found to increase with increasing Zn contents. Moreover, the result from the calculated longitudinal sound velocity and transverse sound velocity indicated that Debye temperature for Zn-doped PbTiO3had more than PbTiO3. Although the Zn-doped PbTiO3has no reported data for comparisons, it is predicted that Zn-doped PbTiO3can improve mechanical and dynamics behavior. [ABSTRACT FROM AUTHOR]

At ambient pressure both CaTe and SrTe are known to exist in NaCl type structure (B1 phase) and undergo structural transition at high pressure to CsCl type structure (B2 phase). Most theoretical studies presented regarding the structural transition from B1 to B2 phase are based upon enthalpy comparisons. In this paper, we have computed elastic constants C 11 , C 12 , and C 44 for both phases at various pressures and used Born stability conditions to compare the relative mechanical stability of both phases with pressure. The dynamical stability of these structures has been investigated using phonon dispersion calculations at different pressures. Our study finds that phonon dispersion calculations match well with enthalpy based predictions for the transition from B1 to B2 phase. Moreover, the Born stability conditions are necessary but not sufficient conditions to predict the structural stability of a crystal. Both CaTe and SrTe are 3D Dirac metals in the B2 phase and exhibit linear dispersions of electronic states near the Fermi level. [Display omitted] • Structural transition from B1 to B2 phase in CaTe and SrTe. • The Dirac-like dispersions are found in high pressure B2 phase of both CaTe and SrTe. • Dirac-like dispersions result from the hybridization of Ca/Sr d x 2 - y 2 and d z 2 and Te- p states. [ABSTRACT FROM AUTHOR]

In this paper, the phase transition mechanism and device conversion performance of the Sb/GeTe superlattice-like films were studied and showed improved amorphous thermal stability and resistance drift compared to the pure Sb films. Transmission electron microscopy showed that the Sb layer plays a leading role in the crystallization process, forming a large number of Sb grains. The metallic behavior of the Sb/GeTe thin films was confirmed by density functional theory calculations. The thermal conductivity of the crystalline film was found to be higher than that of the amorphous film, and the thermal conductivity of the Sb/GeTe film was lower than that of the other monolayer films. In the Sb/GeTe film, the Sb–Sb and Ge–Te bonds were the main bond structures, and some Sb–Te bonds were formed at the layer interfaces, enhancing the stability of the film. Laser picosecond measurements showed that Sb/GeTe film had a higher crystallization rate than the GeTe film. The phase change memory devices based on the Sb/GeTe thin films were found to have lower operational power consumption and higher transition speed. These results showed that the Sb/GeTe thin film explored in this study was a promising phase change storage thin film with excellent performance. ● The coupling effect of multiple interfaces in Sb/GeTe superlattice films were investigated in detail. ● The redistribution of the atoms after crystallization was observed. ● The energy band structure of the Sb/GeTe superlattice films was obtained by density functional theory calculations. ● The interface coupling improved the phase transition behavior and the phase transition performance. [ABSTRACT FROM AUTHOR]

In this paper, spin-polarized periodic density functional theory-based simulations were performed to investigate H 2 S adsorption and dissociation on the defective and strained Fe (110) surfaces which exist in real oil exploitation and transport. It was found that the defective surface facilitates H 2 S adsorption and dissociation with respect to the perfect surface, while the homogeneous external stresses, giving rise to uniform lattice expansion, show negligible effects for the strain estimated from experiment. More interestingly, the simulations predicted a correct order of phase transition at the Fe (110) surface by using the chemical potential based thermodynamic model, that is, from the elementary Fe crystal to the FeS crystal to the FeS 2 crystal to the elementary S crystal with the S coverage on the Fe (110) surface increasing. [Display omitted] [ABSTRACT FROM AUTHOR]

• First principles statistical mechanics method was used to detect phase transition. • Quantify uncertainty of phase transition locations due to cluster expansion fittings. • Chebyshev basis function shifted the transition locations toward the dilute phase. • Perturbed defect configurations lowered the order-disorder transition temperature. • Weighting of low temperature DFT data has minor effect on the transition locations. Predicting phase diagrams from first principle calculations eliminates the need of tedious experimental trials and errors. Fully automating first principle phase diagram calculations without any sort of human intervention has been a long daunting task and troubling scientific communities for decades. This grand problem remains not fully resolved, largely due to the vastly high-dimensional parameter space associated with density functional theory, cluster expansion, lattice Monte Carlo, and the substantial uncertainty propagating through a set of complex simulations. As a first step to tackle this grand problem, we reported a first demonstration of how sensitive phase boundary locations can be to various cluster expansion fittings and input DFT training data. To the best knowledge of the authors, this study reported the first ever attempt to quantify uncertainty in first principles statistical mechanics framework. In addition, a semi-automated phase transition detection algorithm has been devised in this paper to deal with the associated statistical errors and uncertainties from Monte Carlo method and its predecessor DFT calculations and cluster expansions. This algorithm has been applied in a classical cluster expansion Mg-Cd binary alloy system to detect phase transitions at various locations of phase diagram using different cluster expansions to demonstrate its predictive power and quantify uncertainties. The results suggested that using Chebyshev basis function shifted the transition locations toward the dilute solid solution phase and expanded the phase stability of concentrated ordered phases to wider composition range. The addition of perturbed defect configurations into training data set lowered the order-disorder transition temperature to be away from true transition temperature, suggesting the transition nature is indeed configurational disorder dominated rather than defect assisted. We found that the weighting has negligible effect on the transition locations, except for the case of using Chebyshev basis function to fit all non-weighted configurations that can be susceptible to Monte Carlo sampling hysteresis. [ABSTRACT FROM AUTHOR]

In the process of heating, atomic thermal motion causes an increase in Cu or Zn anti-sites and the degree to which atoms randomly occupy sublattices. The disordered solid solution can be separated into partially disordered and fully disordered solid solutions, and the transition from a fully ordered structure to a fully disordered structure of the solid solution should occur as an evolutionary process of atoms that randomly occupy sublattices to different degrees. In this paper, the concept of "disorder degree" is proposed, and a pseudo-atomic lattice inversion potential method is used to simulate the order to disorder transition of CuZn solid solution. The potential parameters can be obtained using density functional theory (DFT) calculation and Chen's lattice inversion method. The results indicate that the lattice distortion exhibits a quadratic relationship in which the disorder degree weakens the cohesive energy in the order-disorder transition process. The calculated vibrational entropy difference between the fully ordered B 2 and fully disordered A 2 CuZn solid solution is 0.24 k B /atom. Furthermore, a new pseudo-atom γ -(Zn or Cu) system is built to calculate the thermodynamic properties of a non-stoichiometry Cu-Zn alloy system, and the results show that the vibrational entropy, specific heat capacity, and bulk modulus exhibit an approximately linear change with Zn concentration. The vibrational entropy and bulk modulus are sensitive to the phase transition, and the slope mutation facilitates the determination of the phase boundary. The order-disorder transition of the solid solution can be treated as an evolutionary process of atoms that randomly occupy sublattices to different degrees. Image 1 [ABSTRACT FROM AUTHOR]

By means of classical density functional theory and its dynamical extension, we consider a colloidal fluid with spherically symmetric competing interactions, which are well known to exhibit a rich bulk phase behavior. This includes complex three-dimensional periodically ordered cluster phases such as lamellae, two-dimensional hexagonally packed cylinders, gyroid structures, or spherical micelles. While the bulk phase behavior has been studied extensively in earlier work, in this paper we focus on such structures confined between planar repulsive walls under shear flow. For sufficiently high shear rates, we observe that microphase separation can become fully suppressed. For lower shear rates, however, we find that, e.g., the gyroid structure undergoes a kinetic phase transition to a hexagonally packed cylindrical phase, which is found experimentally and theoretically in amphiphilic block copolymer systems. As such, besides the known similarities between the latter and colloidal systems regarding the equilibrium phase behavior, our work reveals further intriguing nonequilibrium relations between copolymer melts and colloidal fluids with competing interactions. [ABSTRACT FROM AUTHOR]

Describing correlated electron systems near phase transitions has been a major challenge in computational condensed-matter physics. In this paper, we apply highly accurate fixed-node quantum Monte Carlo techniques, which directly work with many-body wave functions and simulate electron correlations, to investigate the metal-to-insulator transition of a correlated hydrogen lattice. By calculating spin and charge properties, and analyzing the low-energy Hilbert space, we identify the transition point and identify order parameters that can be used to detect the transition. Our results provide a benchmark for density functional theories seeking to treat correlated electron systems. [ABSTRACT FROM AUTHOR]

To improve the high-temperature capability of 718-type wrought nickel-base superalloys, the -phase () can be stabilized. However, this also reduces the size of the forging window because forging has to be done above the - and below the solvus temperature of the phase that is used to enable fine-grain forging, i.e. the δ-phase of type or the η-phase of -type. Understanding the influence of alloying elements on the formation of these phases is therefore important. In this paper, density functional theory calculations at 0 K are performed to determine the stabilizing effect of aluminium and of the transition group elements on the stability of the δ-phase and η-phase. Most of the transition group elements of 5th and 6th period stabilize the δ-phase, whereas the stabilizing effect on the η-phase is weaker. According to the calculations, Mo, Tc, W, Re, and Os may be expected to stabilize the δ-phase but not the η-phase, whereas Al and Zn strongly stabilize the η-phase. V, Zr, Ru, Rh, Pd, Ag, Cd, Hf, Ta, Ir, Pt, Au, and Hg stabilize both phases. For some elements (Cr, Mn, Fe, Co), magnetic effects in the δ and especially in the η-phase are shown to be significant at the concentrations studied here. [ABSTRACT FROM AUTHOR]