Fractional molecular field theory(FMFT)is a phenomenological theory that describes phase transitions in crystals with randomly distributed components,such as the relaxor-ferroelectrics and spin glasses.In order to ver...Fractional molecular field theory(FMFT)is a phenomenological theory that describes phase transitions in crystals with randomly distributed components,such as the relaxor-ferroelectrics and spin glasses.In order to verify the feasibility of this theory,this paper fits it to the Monte Carlo simulations of specific heat and susceptibility versus temperature of two-dimensional(2D)random-site Ising model(2D-RSIM).The results indicate that the FMFT deviates from the 2D-RSIM significantly.The main reason for the deviation is that the 2D-RSIM is a typical system of component random distribution,where the real order parameter is spatially heterogeneous and has no symmetry of space translation,but the basic assumption of FMFT means that the parameter is spatially uniform and has symmetry of space translation.展开更多
The phase transition of gallium phosphide (GAP) from zinc-blende (ZB) to a rocksalt (RS) structure is investigated by the plane-wave pseudopotential density functional theory (DFT). Lattice constant a0, elasti...The phase transition of gallium phosphide (GAP) from zinc-blende (ZB) to a rocksalt (RS) structure is investigated by the plane-wave pseudopotential density functional theory (DFT). Lattice constant a0, elastic constants cij, bulk modulus B0 and the pressure derivative of bulk modulus B0 are calculated. The results are in good agreement with numerous experimental and theoretical data. From the usual condition of equal enthalpies, the phase transition from the ZB to the RS structure occurs at 21.9 GPa, which is close to the experimental value of 22.0 GPa. The elastic properties of GaP with the ZB structure in a pressure range from 0 GPa to 21.9 GPa and those of the RS structure in a pressure range of pressures from 21.9 GPa to 40 GPa are obtained. According to the quasi-harmonic Debye model, in which the phononic effects are considered, the normalized volume V/Vo, the Debye temperature 8, the heat capacity Cv and the thermal expansion coefficient a are also discussed in a pressure range from 0 CPa to 40 GPa and a temperature range from 0 K to 1500 K.展开更多
In this contribution results from different disciplines of science were compared to show their intimate interweaving with each other having in common the golden ratio <i><span style="font-family:Verdana;...In this contribution results from different disciplines of science were compared to show their intimate interweaving with each other having in common the golden ratio <i><span style="font-family:Verdana;">φ</span></i><span style="font-family:Verdana;"> respectively its fifth power </span><i><span style="font-family:Verdana;">φ</span></i><sup><span style="font-family:Verdana;">5</span></sup><span style="font-family:Verdana;">. The research fields cover model calculations of statistical physics associated with phase transitions, the quantum probability of two particles, new physics of everything suggested by the information relativity theory (</span><i><span style="font-family:Verdana;">IRT</span></i><span style="font-family:Verdana;">) including explanations of cosmological relevance, the </span><i><span style="font-family:Verdana;">ε</span></i><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">infinity theory, superconductivity, and the </span><i><span style="font-family:Verdana;">Tammes</span></i><span style="font-family:Verdana;"> problem of the largest diameter of </span><i><span style="font-family:Verdana;">N</span></i><span style="font-family:Verdana;"> non-overlapping circles on the surface of a sphere with its connection to viral morphology and crystallography. Finally, </span><i><span style="font-family:Verdana;">Fibo</span><span style="font-family:Verdana;">nacci</span></i><span style="font-family:Verdana;"> anyons proposed for topological quantum</span><span style="font-family:Verdana;"> computation (</span><i><span style="font-family:Verdana;">TQC</span></i><span style="font-family:Verdana;">) were briefly described in comparison to the recently formulated reverse </span><i><span style="font-family:Verdana;">Fibonacci</span></i><span style="font-family:Verdana;"> approach using the </span><span style="font-family:Verdana;"><em>Jani</em></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="white-space:nowrap;"><em>č</em></span><em>ko</em></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> number sequence. An architecture applicable for a quantum computer is proposed consisting of 13-step twisted microtubules similar to tubulin microtubules of living matter. Most topics point to the omnipresence of the golden mean as the numerical dominator of our world.</span></span></span>展开更多
The kinetics of nucleation of phase transition is a phenomenal theory.Some new technologies of preparation of nanomaterials,for example,by shock wave and by electropulsing,are pulse interactions.Based on the known non...The kinetics of nucleation of phase transition is a phenomenal theory.Some new technologies of preparation of nanomaterials,for example,by shock wave and by electropulsing,are pulse interactions.Based on the known nonlinear theories of phase transition,the nonlinear kinetics of phase transition is discussed,and a soliton-like model is proposed. This mathematical method can not only explain the basic characteristics of pulse interactions and suddenness of phase transition, and possesses a consistency of mechanism for nucleation and growth.展开更多
With first-principles virtual-crystal approximation calculations, we systematically investigate the geometric and elec- tronic structures as well as the phase transition of lead zirconate titanate (PbZr 1-xTixO3 or ...With first-principles virtual-crystal approximation calculations, we systematically investigate the geometric and elec- tronic structures as well as the phase transition of lead zirconate titanate (PbZr 1-xTixO3 or PZT) as a function of Ti content for the whole range of 0 〈 XTi 〈 1. It can be found that, with the increase of the Ti content, the PbZr1-xTixO3 solid solutions undergo a rhombohedral-to-tetragonal phase transition, which is consistent with the experimental results. In addition, we also show the evolution in geometric and electronic structures of rhombohedral and tetragonal PbZr1-xTixO3 with the increasing content of Ti.展开更多
Simple Landau free energy function is presented to describe the Liquid-RII-RI phase sequence of alkanes and transitions between them. The order parameters necessary to describe these rotator phase transitions are iden...Simple Landau free energy function is presented to describe the Liquid-RII-RI phase sequence of alkanes and transitions between them. The order parameters necessary to describe these rotator phase transitions are identified. We present a mean-field description of the Liquid-RII and Liquid-RI transitions. General arguments are presented for the topology of the phase diagram in the vicinity of the Liquid-RII-RI triple point. Within this model the Liquid-RII and Liquid-RI transitions are found to be always strongly first order. Calculations based on this model agree qualitatively with experiments.展开更多
With the developing of the computer, the network is more and more liked by the users. It has become an indispensable part of the living and production. However, with the expanding of network scale, there have been som...With the developing of the computer, the network is more and more liked by the users. It has become an indispensable part of the living and production. However, with the expanding of network scale, there have been some problems in the operation of the network system. Most of people lack of understanding on these issues, so they couldn' t handle them well. Some people use the theory of phase transitions to explain the power law phenomena in computer network. But it only start from the theory, but ignores the correlation of network nodes. The lack of holistic thinking mode, make the development of computer network get into a stray area. This paper started from the phase transition theory, elaborated the connotations of phase transformation and the overall correlation, and described the problems about them.展开更多
In this paper the first-principles calculations within local spin density approximation (LSDA)+U show that BiFeO3 experiences a mixed phase state with P4mm structure being the intermediate phase before the pressure...In this paper the first-principles calculations within local spin density approximation (LSDA)+U show that BiFeO3 experiences a mixed phase state with P4mm structure being the intermediate phase before the pressure of phase transition is reached. The critical pressure for the insulator-metal transition (IMT) is found to be about 50 GPa. A pressure induced crossover of high-spin states and low-spin states is observed close to the IMT pressure in R3c structure. The LSDA+U calculations account well for the mechanism of the IMT and crossover of spin states predicted in recent experiment (Ref.[1]).展开更多
We investigate the effect of interaction, temperature, and anisotropic parameter on the quantum phase transitions in an anisotropic square-octagon lattice with fermions under the framework of the single band Hubbard m...We investigate the effect of interaction, temperature, and anisotropic parameter on the quantum phase transitions in an anisotropic square-octagon lattice with fermions under the framework of the single band Hubbard model through using the combination of cellular dynamical mean field theory and a continuous time Monte Carlo algorithm. The competition between interaction and temperature shows that with the increase of the anisotropic parameter, the critical on-site repulsive interaction for the metal-insulator transition increases for fixed temperature. The interaction-anisotropic parameter phase diagram reveals that with the decrease of temperature, the critical anisotropic parameter for the Mott transition will increase for fixed interaction cases.展开更多
The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory(DFT). Varying from 3D to 2D four VSe2 structures, bulk 2H-...The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory(DFT). Varying from 3D to 2D four VSe2 structures, bulk 2H-VSe2 and 1T-VSe2, monolayer H-VSe2 and T-VSe2 are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe2 is semimetallic whereas T-VSe2 is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe2 transforms to T-VSe2, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe2, which suggests potential applications as high-performance functional nanomaterial.展开更多
The martensitic-type phase transformation paths from the rutile to theα-PbO2 phase of TiO2 are studied with linear interpolation and NEB/G-SSNEB methods based on first-principles calculations.Its potential energy sur...The martensitic-type phase transformation paths from the rutile to theα-PbO2 phase of TiO2 are studied with linear interpolation and NEB/G-SSNEB methods based on first-principles calculations.Its potential energy surface and the lowest energy path are revealed.Our results indicate that the titanium atoms of the rutile phase shuffle along the[0-11]rut crystal direction to form theα-PbO2 phase.During the phase transition,the oxygen atoms are dragged by the heavier titanium atoms and then reach their new equilibrium positions.The barrier of phase transition from nudged elastic band theory is about 231 meV,which is qualitatively consistent with previous theoretical calculations from the monoclinic phase to the tetragonal phase for ZrO2 and HfO2.Debye model can also be successfully used to predict the pressure and temperature of the phase transformation.展开更多
Bulk iridium ditelluride(IrTe2)is a layered material and is known for its interesting electronic and structural properties,such as large spin-orbit coupling,charge ordering,and superconductivity.However,so far there i...Bulk iridium ditelluride(IrTe2)is a layered material and is known for its interesting electronic and structural properties,such as large spin-orbit coupling,charge ordering,and superconductivity.However,so far there is no experimental study about the fabrication of monolayer IrTe2.Here we report the formation of IrTe2 monolayer on Ir(111)substrate by direct tellurization method.Scanning tunneling microscope(STM)images show the coexistence of 1/5 phase and 1/6 phase structures of IrTe2 at room temperature.We also obtained STM images showing distorted stripe feature under low temperatures.This stripe feature is possibly induced by the strain between the IrTe2 monolayer and the metal substrate.Density functional theory(DFT)calculations show that the IrTe2 monolayer has strong interaction with the underlying Ir(111)substrate.展开更多
Monolayer transition metal dichalcogenides can normally exist in several structural polymorphs with distinct electrical,optical,and catalytic properties.Effective control of the relative stability and transformation o...Monolayer transition metal dichalcogenides can normally exist in several structural polymorphs with distinct electrical,optical,and catalytic properties.Effective control of the relative stability and transformation of different phases in these materials is thus of critical importance for applications.Using density functional theory calculations,we investigate the effects of low-work-function metal substrates including Ti,Zr,and Hf on the structural,electronic,and catalytic properties of monolayer MoS_(2) and WS_(2).The results indicate that such substrates not only convert the energetically stable structure from the 1H phase to the 1T'/1T phase,but also significantly reduce the kinetic barriers of the phase transformation.Furthermore,our calculations also indicate that the 1T' phase of MoS_(2) with Zr or Hf substrate is a potential catalyst for the hydrogen evolution reaction.展开更多
Based on the critical unstable of both crystal and magnetic structure of Gd-intermetallic compound near the competition of two strongly independent subsystem ("local 4f7" and "conduction electron concentration")...Based on the critical unstable of both crystal and magnetic structure of Gd-intermetallic compound near the competition of two strongly independent subsystem ("local 4f7" and "conduction electron concentration"), a new QPT (quantum point transition) is predicted by calculation of: (1) The band structure and density of state by density functional theory where a strong narrowing fluidity of fermions around EF with shifted to negative value "-0.8 eV "is observable in the Gd-intermetalliccompound system while in the Y-case, it is not dominated. An antiferromagnetic state on the fluidity of conduction band can be investigated; (2) The internal magnetic field due to short range exchange interaction Jij between the nearest neighbor of local magnetic moment of stable s-state of Gd (L = 0) through the mean field approximation and of Eigenvalue-Eigenfunction ~.(k) are calculated. While a strong negative value of Jy is predicted, the eigenvalue L(k) of the system shows a strong antiferromagnetic phase in the reciprocal lattice direction 〈010〉, 〈001〉 in the correlation length 3.38 ~A. Although the antiferromagnetic state at Rc 〈_ 3.38 °A is a puzzle but it is completely dominated at Rc = 9 °A after passing through the competition between ).λmin(O) and λmin(π) in the ranger of 3.2 °A 〈 Rc 〈 9 °A. Since both of the antiferromagnetic subsystems are sensitive to the predicted KF, the effect of decreasing of conduction electron is proposed to investigate, the change of the antiferromagnetic ordering state to the competition of ferromagnetic state (in direction 〈010〉) and antiferromagnetic state (in direction 〈001 〉 and 〈 100〉) resulted to paramagnetic state in the long range Rc = 9 °A.展开更多
Bacterial flagellar filament can undergo a stress-induced polymorphic phase transition in both vitro and vivo environments.The filament has 12 different helical forms(phases) characterized by different pitch lengths a...Bacterial flagellar filament can undergo a stress-induced polymorphic phase transition in both vitro and vivo environments.The filament has 12 different helical forms(phases) characterized by different pitch lengths and helix radii.When subjected to the frictional force of flowing fluid,the filament changes between a left-handed normal phase and a right-handed semi-coiled phase via phase nucleation and growth.This paper develops non-local finite element method(FEM) to simulate the phase transition under a displacement-controlled loading condition(controlled helix-twist).The FEM formulation is based on the Ginzburg-Landau theory using a one-dimensional non-convex and non-local continuum model.To describe the processes of the phase nucleation and growth,viscosity-type kinetics is also used.The non-local FEM simulation captures the main features of the phase transition:two-phase coexistence with an interface of finite thickness,phase nucleation and phase growth with interface propagation.The non-local FEM model provides a tool to study the effects of the interfacial energy/thickness and loading conditions on the phase transition.展开更多
We investigate the structural and thermodynamic properties of OsN2 by a plane-wave pseudopotential density functional theory method. The obtained lattice constant, bulk modulus and cell volume per unit formula are con...We investigate the structural and thermodynamic properties of OsN2 by a plane-wave pseudopotential density functional theory method. The obtained lattice constant, bulk modulus and cell volume per unit formula are consistent with the available theoretical data. Moreover, the pressure-induced phase transition of OsN2 from pyrite structure to fluorite structure has been obtained. It is found that the transition pressure of OsN2 at zero temperature is 67.2 GPa. The bulk modulus B as well as other thermodynamic quantities of fluorite OsN2 (including the Griineisen constant γ and thermal expansion α) on temperatures and pressures have also been obtained.展开更多
The symmetric and the asymmetric double-chain Bose-Hubbard Models( BHMs) are studied by the mean-field theory. By using Landau's quantum phase transition theory,phase diagrams for systems with different hopping en...The symmetric and the asymmetric double-chain Bose-Hubbard Models( BHMs) are studied by the mean-field theory. By using Landau's quantum phase transition theory,phase diagrams for systems with different hopping energies and repulsive interactions are obtained. Thereby,Mott-insulator-superfluid( MISF)phase transition boundaries are determined. Our results show that tunneling effects between two chains provide additional channels for particles hopping between corresponding optical lattice sites of different chains,which makes easier for systems to transit from MI to SF phase. The two-site parity function is also utilized to investigate the properties of the system near the quantum phase transit point.We found that the increase of inter-chain hopping will reinforce the tunneling effects between two chains,and reduce the intrachain tunneling effects within the same chain.展开更多
As an analytical method, the effective-field theory (EFT) is used to study the dynamical response of the kinetic Ising model in the presence of a sinusoidal oscillating field. The effective-field equations of motion...As an analytical method, the effective-field theory (EFT) is used to study the dynamical response of the kinetic Ising model in the presence of a sinusoidal oscillating field. The effective-field equations of motion of the average magnetization are given for the honeycomb lattice (Z = 3). The Liapunov exponent A is calculated for discussing the stability of the magnetization and it is used to determine the phase boundary. In the field amplitude ho / ZJ-temperature T/ZJ plane, the phase boundary separating the dynamic ordered and the disordered phase has been drawn. In contrast to previous analytical results that predicted a tricritical point separating a dynamic phase boundary line of continuous and discontinuous transitions, we find that the transition is always continuous. There is inconsistency between our results and previous analytical results, because they do not introduce sufficiently strong fluctuations.展开更多
We report a density functional theory study of a phase transition of a VS2 monolayer that can be tuned by the in-plane biaxial strain. This results in both a metal-insulator transition and a low spin-high spin magneti...We report a density functional theory study of a phase transition of a VS2 monolayer that can be tuned by the in-plane biaxial strain. This results in both a metal-insulator transition and a low spin-high spin magnetic transition. At low temperature, the semiconducting H-phase is stable and large strain (〉3%) is required to provoke the transition. On the other hand, at room temperature (300 K), only a small tensile strain of 2% is needed to induce the phase transition from the semiconducting H-phase to the metallic T-phase together with the magnetic transition from high spin to low spin. The phase diagram dependence on both strain and temperature is also discussed in order to provide a better understanding of the phase stability of VS2 monolayers.展开更多
The molecular field theory (MF) of nematic to isotropic (N-I) phase transition in surface-aligned nematic film is proposed by using Lebwohl-Lasher model. The calculated results indicate that the N-I-phase transition w...The molecular field theory (MF) of nematic to isotropic (N-I) phase transition in surface-aligned nematic film is proposed by using Lebwohl-Lasher model. The calculated results indicate that the N-I-phase transition will be strongly affected by the interaction between liquid crystal molecules and substrate. The nematic film can be divided into three regions according to their phase transition behavior: the interface, the bulk and the free surface. The interface phase transition depends strongly on the strength of interaction between liquid crystal and substrate, and its phase transition temperature is higher than that of bulk phase transition. Especially, the order parameter will become a continuous function of temperature when the anchoring energy is strong enough. In the bulkregion, the N-I phase transition is still of the first order while in the free surface, the N-I phase transition belongs to the typical second order transition behaviour. When the temperature is increased, the N-I phase transition starts in the free surface region and then extends to the bulk and interface regions gradually. All these results are confirmed by Monte Carlo (MC) study and agree with the Landau-de Gennes theory.展开更多
基金Project supported by the Open Project of the Key Laboratory of Xinjiang Uygur Autonomous Region,China(Grant No.2021D04015)the Yili Kazakh Autonomous Prefecture Science and Technology Program Project,China(Grant No.YZ2022B021).
文摘Fractional molecular field theory(FMFT)is a phenomenological theory that describes phase transitions in crystals with randomly distributed components,such as the relaxor-ferroelectrics and spin glasses.In order to verify the feasibility of this theory,this paper fits it to the Monte Carlo simulations of specific heat and susceptibility versus temperature of two-dimensional(2D)random-site Ising model(2D-RSIM).The results indicate that the FMFT deviates from the 2D-RSIM significantly.The main reason for the deviation is that the 2D-RSIM is a typical system of component random distribution,where the real order parameter is spatially heterogeneous and has no symmetry of space translation,but the basic assumption of FMFT means that the parameter is spatially uniform and has symmetry of space translation.
文摘The phase transition of gallium phosphide (GAP) from zinc-blende (ZB) to a rocksalt (RS) structure is investigated by the plane-wave pseudopotential density functional theory (DFT). Lattice constant a0, elastic constants cij, bulk modulus B0 and the pressure derivative of bulk modulus B0 are calculated. The results are in good agreement with numerous experimental and theoretical data. From the usual condition of equal enthalpies, the phase transition from the ZB to the RS structure occurs at 21.9 GPa, which is close to the experimental value of 22.0 GPa. The elastic properties of GaP with the ZB structure in a pressure range from 0 GPa to 21.9 GPa and those of the RS structure in a pressure range of pressures from 21.9 GPa to 40 GPa are obtained. According to the quasi-harmonic Debye model, in which the phononic effects are considered, the normalized volume V/Vo, the Debye temperature 8, the heat capacity Cv and the thermal expansion coefficient a are also discussed in a pressure range from 0 CPa to 40 GPa and a temperature range from 0 K to 1500 K.
文摘In this contribution results from different disciplines of science were compared to show their intimate interweaving with each other having in common the golden ratio <i><span style="font-family:Verdana;">φ</span></i><span style="font-family:Verdana;"> respectively its fifth power </span><i><span style="font-family:Verdana;">φ</span></i><sup><span style="font-family:Verdana;">5</span></sup><span style="font-family:Verdana;">. The research fields cover model calculations of statistical physics associated with phase transitions, the quantum probability of two particles, new physics of everything suggested by the information relativity theory (</span><i><span style="font-family:Verdana;">IRT</span></i><span style="font-family:Verdana;">) including explanations of cosmological relevance, the </span><i><span style="font-family:Verdana;">ε</span></i><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">infinity theory, superconductivity, and the </span><i><span style="font-family:Verdana;">Tammes</span></i><span style="font-family:Verdana;"> problem of the largest diameter of </span><i><span style="font-family:Verdana;">N</span></i><span style="font-family:Verdana;"> non-overlapping circles on the surface of a sphere with its connection to viral morphology and crystallography. Finally, </span><i><span style="font-family:Verdana;">Fibo</span><span style="font-family:Verdana;">nacci</span></i><span style="font-family:Verdana;"> anyons proposed for topological quantum</span><span style="font-family:Verdana;"> computation (</span><i><span style="font-family:Verdana;">TQC</span></i><span style="font-family:Verdana;">) were briefly described in comparison to the recently formulated reverse </span><i><span style="font-family:Verdana;">Fibonacci</span></i><span style="font-family:Verdana;"> approach using the </span><span style="font-family:Verdana;"><em>Jani</em></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="white-space:nowrap;"><em>č</em></span><em>ko</em></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> number sequence. An architecture applicable for a quantum computer is proposed consisting of 13-step twisted microtubules similar to tubulin microtubules of living matter. Most topics point to the omnipresence of the golden mean as the numerical dominator of our world.</span></span></span>
文摘The kinetics of nucleation of phase transition is a phenomenal theory.Some new technologies of preparation of nanomaterials,for example,by shock wave and by electropulsing,are pulse interactions.Based on the known nonlinear theories of phase transition,the nonlinear kinetics of phase transition is discussed,and a soliton-like model is proposed. This mathematical method can not only explain the basic characteristics of pulse interactions and suddenness of phase transition, and possesses a consistency of mechanism for nucleation and growth.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11104203, 11075116, 50972014, 51072024, and 51132002)the Foundation of Introduction of Talent of Tianjin Normal University, China (Grant No. 5RL100)
文摘With first-principles virtual-crystal approximation calculations, we systematically investigate the geometric and elec- tronic structures as well as the phase transition of lead zirconate titanate (PbZr 1-xTixO3 or PZT) as a function of Ti content for the whole range of 0 〈 XTi 〈 1. It can be found that, with the increase of the Ti content, the PbZr1-xTixO3 solid solutions undergo a rhombohedral-to-tetragonal phase transition, which is consistent with the experimental results. In addition, we also show the evolution in geometric and electronic structures of rhombohedral and tetragonal PbZr1-xTixO3 with the increasing content of Ti.
文摘Simple Landau free energy function is presented to describe the Liquid-RII-RI phase sequence of alkanes and transitions between them. The order parameters necessary to describe these rotator phase transitions are identified. We present a mean-field description of the Liquid-RII and Liquid-RI transitions. General arguments are presented for the topology of the phase diagram in the vicinity of the Liquid-RII-RI triple point. Within this model the Liquid-RII and Liquid-RI transitions are found to be always strongly first order. Calculations based on this model agree qualitatively with experiments.
文摘With the developing of the computer, the network is more and more liked by the users. It has become an indispensable part of the living and production. However, with the expanding of network scale, there have been some problems in the operation of the network system. Most of people lack of understanding on these issues, so they couldn' t handle them well. Some people use the theory of phase transitions to explain the power law phenomena in computer network. But it only start from the theory, but ignores the correlation of network nodes. The lack of holistic thinking mode, make the development of computer network get into a stray area. This paper started from the phase transition theory, elaborated the connotations of phase transformation and the overall correlation, and described the problems about them.
文摘In this paper the first-principles calculations within local spin density approximation (LSDA)+U show that BiFeO3 experiences a mixed phase state with P4mm structure being the intermediate phase before the pressure of phase transition is reached. The critical pressure for the insulator-metal transition (IMT) is found to be about 50 GPa. A pressure induced crossover of high-spin states and low-spin states is observed close to the IMT pressure in R3c structure. The LSDA+U calculations account well for the mechanism of the IMT and crossover of spin states predicted in recent experiment (Ref.[1]).
基金supported by the National Natural Science Foundation of China(Grant Nos.11174169,11234007,and 51471093)
文摘We investigate the effect of interaction, temperature, and anisotropic parameter on the quantum phase transitions in an anisotropic square-octagon lattice with fermions under the framework of the single band Hubbard model through using the combination of cellular dynamical mean field theory and a continuous time Monte Carlo algorithm. The competition between interaction and temperature shows that with the increase of the anisotropic parameter, the critical on-site repulsive interaction for the metal-insulator transition increases for fixed temperature. The interaction-anisotropic parameter phase diagram reveals that with the decrease of temperature, the critical anisotropic parameter for the Mott transition will increase for fixed interaction cases.
基金Funded by the National Natural Science Foundation of China(No.11547115)the Science Research Foundation for Ph D of Liaoning Province(No.201501091)
文摘The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory(DFT). Varying from 3D to 2D four VSe2 structures, bulk 2H-VSe2 and 1T-VSe2, monolayer H-VSe2 and T-VSe2 are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe2 is semimetallic whereas T-VSe2 is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe2 transforms to T-VSe2, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe2, which suggests potential applications as high-performance functional nanomaterial.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51872227,51572219,and 11447030).
文摘The martensitic-type phase transformation paths from the rutile to theα-PbO2 phase of TiO2 are studied with linear interpolation and NEB/G-SSNEB methods based on first-principles calculations.Its potential energy surface and the lowest energy path are revealed.Our results indicate that the titanium atoms of the rutile phase shuffle along the[0-11]rut crystal direction to form theα-PbO2 phase.During the phase transition,the oxygen atoms are dragged by the heavier titanium atoms and then reach their new equilibrium positions.The barrier of phase transition from nudged elastic band theory is about 231 meV,which is qualitatively consistent with previous theoretical calculations from the monoclinic phase to the tetragonal phase for ZrO2 and HfO2.Debye model can also be successfully used to predict the pressure and temperature of the phase transformation.
基金Project supported by the National Key Research&Development Project of China(Grant Nos.2019YFA0308500,2018YFA0305800,and 2016YFA0202300)the National Natural Science Foundation of China(Grant Nos.51991340,61888102,and 11888101)the Chinese Academy of Sciences(Grant Nos.XDB28000000 and XDB30000000).
文摘Bulk iridium ditelluride(IrTe2)is a layered material and is known for its interesting electronic and structural properties,such as large spin-orbit coupling,charge ordering,and superconductivity.However,so far there is no experimental study about the fabrication of monolayer IrTe2.Here we report the formation of IrTe2 monolayer on Ir(111)substrate by direct tellurization method.Scanning tunneling microscope(STM)images show the coexistence of 1/5 phase and 1/6 phase structures of IrTe2 at room temperature.We also obtained STM images showing distorted stripe feature under low temperatures.This stripe feature is possibly induced by the strain between the IrTe2 monolayer and the metal substrate.Density functional theory(DFT)calculations show that the IrTe2 monolayer has strong interaction with the underlying Ir(111)substrate.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0204904 and 2019YFA0210004)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB30000000)the Fundamental Research Funds for the Central Universities,China(Grant No.WK3510000013).
文摘Monolayer transition metal dichalcogenides can normally exist in several structural polymorphs with distinct electrical,optical,and catalytic properties.Effective control of the relative stability and transformation of different phases in these materials is thus of critical importance for applications.Using density functional theory calculations,we investigate the effects of low-work-function metal substrates including Ti,Zr,and Hf on the structural,electronic,and catalytic properties of monolayer MoS_(2) and WS_(2).The results indicate that such substrates not only convert the energetically stable structure from the 1H phase to the 1T'/1T phase,but also significantly reduce the kinetic barriers of the phase transformation.Furthermore,our calculations also indicate that the 1T' phase of MoS_(2) with Zr or Hf substrate is a potential catalyst for the hydrogen evolution reaction.
文摘Based on the critical unstable of both crystal and magnetic structure of Gd-intermetallic compound near the competition of two strongly independent subsystem ("local 4f7" and "conduction electron concentration"), a new QPT (quantum point transition) is predicted by calculation of: (1) The band structure and density of state by density functional theory where a strong narrowing fluidity of fermions around EF with shifted to negative value "-0.8 eV "is observable in the Gd-intermetalliccompound system while in the Y-case, it is not dominated. An antiferromagnetic state on the fluidity of conduction band can be investigated; (2) The internal magnetic field due to short range exchange interaction Jij between the nearest neighbor of local magnetic moment of stable s-state of Gd (L = 0) through the mean field approximation and of Eigenvalue-Eigenfunction ~.(k) are calculated. While a strong negative value of Jy is predicted, the eigenvalue L(k) of the system shows a strong antiferromagnetic phase in the reciprocal lattice direction 〈010〉, 〈001〉 in the correlation length 3.38 ~A. Although the antiferromagnetic state at Rc 〈_ 3.38 °A is a puzzle but it is completely dominated at Rc = 9 °A after passing through the competition between ).λmin(O) and λmin(π) in the ranger of 3.2 °A 〈 Rc 〈 9 °A. Since both of the antiferromagnetic subsystems are sensitive to the predicted KF, the effect of decreasing of conduction electron is proposed to investigate, the change of the antiferromagnetic ordering state to the competition of ferromagnetic state (in direction 〈010〉) and antiferromagnetic state (in direction 〈001 〉 and 〈 100〉) resulted to paramagnetic state in the long range Rc = 9 °A.
基金supported by the Hong Kong University of Science and Technology and the National Natural Science Foundation of China (10902013)
文摘Bacterial flagellar filament can undergo a stress-induced polymorphic phase transition in both vitro and vivo environments.The filament has 12 different helical forms(phases) characterized by different pitch lengths and helix radii.When subjected to the frictional force of flowing fluid,the filament changes between a left-handed normal phase and a right-handed semi-coiled phase via phase nucleation and growth.This paper develops non-local finite element method(FEM) to simulate the phase transition under a displacement-controlled loading condition(controlled helix-twist).The FEM formulation is based on the Ginzburg-Landau theory using a one-dimensional non-convex and non-local continuum model.To describe the processes of the phase nucleation and growth,viscosity-type kinetics is also used.The non-local FEM simulation captures the main features of the phase transition:two-phase coexistence with an interface of finite thickness,phase nucleation and phase growth with interface propagation.The non-local FEM model provides a tool to study the effects of the interfacial energy/thickness and loading conditions on the phase transition.
基金supported by the National Natural Science Foundation of China (Grant No. 10776022)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090181110080)
文摘We investigate the structural and thermodynamic properties of OsN2 by a plane-wave pseudopotential density functional theory method. The obtained lattice constant, bulk modulus and cell volume per unit formula are consistent with the available theoretical data. Moreover, the pressure-induced phase transition of OsN2 from pyrite structure to fluorite structure has been obtained. It is found that the transition pressure of OsN2 at zero temperature is 67.2 GPa. The bulk modulus B as well as other thermodynamic quantities of fluorite OsN2 (including the Griineisen constant γ and thermal expansion α) on temperatures and pressures have also been obtained.
基金Sponsored by the National Natural Science Foundation China(Grant No.11504106)the Special Foundation for Theoretical Physics Research Program of China(Grant No.11447167)
文摘The symmetric and the asymmetric double-chain Bose-Hubbard Models( BHMs) are studied by the mean-field theory. By using Landau's quantum phase transition theory,phase diagrams for systems with different hopping energies and repulsive interactions are obtained. Thereby,Mott-insulator-superfluid( MISF)phase transition boundaries are determined. Our results show that tunneling effects between two chains provide additional channels for particles hopping between corresponding optical lattice sites of different chains,which makes easier for systems to transit from MI to SF phase. The two-site parity function is also utilized to investigate the properties of the system near the quantum phase transit point.We found that the increase of inter-chain hopping will reinforce the tunneling effects between two chains,and reduce the intrachain tunneling effects within the same chain.
文摘As an analytical method, the effective-field theory (EFT) is used to study the dynamical response of the kinetic Ising model in the presence of a sinusoidal oscillating field. The effective-field equations of motion of the average magnetization are given for the honeycomb lattice (Z = 3). The Liapunov exponent A is calculated for discussing the stability of the magnetization and it is used to determine the phase boundary. In the field amplitude ho / ZJ-temperature T/ZJ plane, the phase boundary separating the dynamic ordered and the disordered phase has been drawn. In contrast to previous analytical results that predicted a tricritical point separating a dynamic phase boundary line of continuous and discontinuous transitions, we find that the transition is always continuous. There is inconsistency between our results and previous analytical results, because they do not introduce sufficiently strong fluctuations.
文摘We report a density functional theory study of a phase transition of a VS2 monolayer that can be tuned by the in-plane biaxial strain. This results in both a metal-insulator transition and a low spin-high spin magnetic transition. At low temperature, the semiconducting H-phase is stable and large strain (〉3%) is required to provoke the transition. On the other hand, at room temperature (300 K), only a small tensile strain of 2% is needed to induce the phase transition from the semiconducting H-phase to the metallic T-phase together with the magnetic transition from high spin to low spin. The phase diagram dependence on both strain and temperature is also discussed in order to provide a better understanding of the phase stability of VS2 monolayers.
基金Project supported by the National Natural Science Foundation of China, Fok Ying Tung Education Foundation and the State Education Commission of China.
文摘The molecular field theory (MF) of nematic to isotropic (N-I) phase transition in surface-aligned nematic film is proposed by using Lebwohl-Lasher model. The calculated results indicate that the N-I-phase transition will be strongly affected by the interaction between liquid crystal molecules and substrate. The nematic film can be divided into three regions according to their phase transition behavior: the interface, the bulk and the free surface. The interface phase transition depends strongly on the strength of interaction between liquid crystal and substrate, and its phase transition temperature is higher than that of bulk phase transition. Especially, the order parameter will become a continuous function of temperature when the anchoring energy is strong enough. In the bulkregion, the N-I phase transition is still of the first order while in the free surface, the N-I phase transition belongs to the typical second order transition behaviour. When the temperature is increased, the N-I phase transition starts in the free surface region and then extends to the bulk and interface regions gradually. All these results are confirmed by Monte Carlo (MC) study and agree with the Landau-de Gennes theory.