arXiv subjects

Ping Zhang

Publications and source records attributed to Ping Zhang.

At least 577 records · Page 32Linked to original sources

arXiv2011

Thermophysical properties for shock compressed polystyrene

We have performed quantum molecular dynamic simulations for warm dense polystyrene at high pressures. The principal Hugoniot up to 790 GPa is derived from wide range equation of states, where contributions from atomic ionizations are semiclassically determined. The optical conductivity is calculated via the Kubo-Greenwood formula, from which the dc electrical conductivity and optical reflectivity are determined. The nonmetal-to-metal transition is identified by gradual decomposition of the polymer. Our results show good agreement with recent high precision laser-driven experiments.

cond-mat.mtrl-sci↗

arXiv2011

Thermodynamic phase transition of uranium trihydride: Role of electronic strong correlation

The electronic structure and thermodynamical properties of uranium trihydrides ($α$-UH$_{3}$ and $β$-UH$_{3}$) have been studied using first-principles density functional theory. We find that inclusion of strong electronic correlation is crucial in successfully depicting the electronic structure and thermodynamic phase stability of uranium hydrides. After turning on the Hubbard parameter, the uranium 5f states are divided into well-resolved multiplets and their metallicity is weakened by downward shift in energy, which prominently changes the hydrogen bond and its vibration frequencies in the system. Without Coulomb repulsion, the experimentally observed $α\mathtt{\rightarrow}β$ phase transition cannot be reproduced, whereas, by inclusion of the on-site correlation, we successfully predict a transition temperature value of about 332 K, which is close to the experimental result.

cond-mat.str-el↗

arXiv2011

Work Function of Single-wall Silicon Carbide Nanotube

Using first-principles calculations, we study the work function of single wall silicon carbide nanotube (SiCNT). The work function is found to be highly dependent on the tube chirality and diameter. It increases with decreasing the tube diameter. The work function of zigzag SiCNT is always larger than that of armchair SiCNT. We reveal that the difference between the work function of zigzag and armchair SiCNT comes from their different intrinsic electronic structures, for which the singly degenerate energy band above the Fermi level of zigzag SiCNT is specifically responsible. Our finding offers potential usages of SiCNT in field-emission devices.

cond-mat.mes-hall↗

arXiv2010

First-principles study of the incorporation and diffusion of helium in cubic zirconia

The incorporation and diffusion of helium (He) with and without intrinsic vacancy defects in cubic ZrO$_{2}$ are investigated through first-principles total-energy calculations, in which the projector-augmented-wave (PAW) method with the generalized gradient approximation (GGA) is used. The calculated formation energies of intrinsic point defects indicate that cubic ZrO$_{2}$ has a tolerant resistance to radiation damage. The incorporation energy of He impurity shows that it is preferable to occupy the Zr vacancy at first, whereas the solution energy suggests that He would be accommodated in the interstitial site at thermodynamic equilibrium concentration. By calculating the He migration energies corresponding to both interstitial and vacancy assisted mechanisms, we suggest that it is most likely for He to diffuse by hopping through a single vacancy. Remarkably, our calculated vacancy-assisted diffusion energy of He is consistent well with the experimental measurement.

cond-mat.mtrl-sci↗

arXiv2010

First-principles calculations of shocked fluid helium in partially ionized region

Quantum molecular dynamic simulations have been employed to study the equation of state (EOS) of fluid helium under shock compressions. The principal Hugoniot is determined from EOS, where corrections from atomic ionization are added onto the calculated data. Our simulation results indicate that principal Hugoniot shows good agreement with gas gun and laser driven experiments, and maximum compression ratio of 5.16 is reached at 106 GPa.

cond-mat.mtrl-sci↗

arXiv2010

Quantum molecular dynamics simulations of lithium melting using Z-method

We performed first-principles molecular dynamics calculations for lithium using the projector augmented waves method and the generalized gradient approximation as exchange-correlation energy. The melting curve of lithium was computed using the \textit{Z}-method technique for pressures up to 30 GPa, which agrees well with the experimental and two-phase simulated results. The change of the melting line slope from positive to negative was predicted by the characteristic shape inversion of the \textit{Z} curve at about 8.2 GPa. Through analyzing the static properties, we conclude that no liquid-liquid phase transition accompanies the occurrence of the melting line maximum, which is caused by the higher compressibility of the liquid phase compared to the solid phase. In addition, we systematically studied the dynamic and optical properties of lithium near melting curve at critical superheating and melting temperatures. It was suggested that spectra difference at critical superheating and melting temperature may be able to diagnose the homogeneous melting.

cond-mat.mtrl-sci↗

arXiv2010

Ideal strengths and bonding properties of PuO2 under tension

We perform a first-principles computational tensile test on PuO$_{2}$ based on density-functional theory within local density approximation (LDA)+\emph{U} formalism to investigate its structural, mechanical, magnetic, and intrinsic bonding properties in the four representative directions: [001], [100], [110], and [111]. The stress-strain relations show that the ideal tensile strengths in the four directions are 81.2, 80.5, 28.3, and 16.8 GPa at strains of 0.36, 0.36, 0.22, and 0.18, respectively. The [001] and [100] directions are prominently stronger than other two directions since that more Pu$-$O bonds participate in the pulling process. Through charge and density of states analysis along the [001] direction, we find that the strong mixed ionic/covalent character of Pu$-$O bond is weakened by tensile strain and PuO$_{2}$ will exhibit an insulator-to-metal transition after tensile stress exceeds about 79 GPa.

cond-mat.mtrl-sci↗

arXiv2010

Sums of large global solutions to the incompressible Navier-Stokes equations

Let G be the (open) set of~$\dot H^{\frac 1 2}$ divergence free vector fields generating a global smooth solution to the three dimensional incompressible Navier-Stokes equations. We prove that any element of G can be perturbed by an arbitrarily large, smooth divergence free vector field which varies slowly in one direction, and the resulting vector field (which remains arbitrarily large) is an element of G if the variation is slow enough. This result implies that through any point in G passes an uncountable number of arbitrarily long segments included in G.

math.AP↗

arXiv2010

Electronic structure, mechanical and thermodynamic properties of ThN from first-principles calculations

Lattice parameter, electronic structure, mechanical and thermodynamic properties of ThN are systematically studied using the projector-augmented-wave method and the generalized gradient approximation based on the density functional theory. The calculated electronic structure indicates the important contributions of Th 6\emph{d}and 5\emph{f} states to the Fermi-level electron occupation. Through Bader analysis it is found that the effective valencies in ThN can be represented as Th$^{+1.82}$ N$^{-1.82}$. Elastic constant calculations shows that ThN is mechanically stable and elastically anisotropic. Furthermore, the melting curve of ThN is presented up to 120 GPa. Based on the phonon dispersion data, our calculated specific heat capacities including both lattice and conduction-electron contributions agree well with experimental results in a wide range of temperature.

cond-mat.mtrl-sci↗

arXiv2010

Chiral topological excitonic insulator in semiconductor quantum wells

We present a scheme to realize the chiral topological excitonic insulator in semiconductor heterostructures which can be experimentally fabricated with a coupled quantum well adjacent to twoferromagnetic insulating films. The different mean-field chiral topological orders, which are due to the change in the directions of the magnetization of the ferromagnetic films, can be characterized by the TKNN numbers in the bulk system as well as by the winding numbers of the gapless states in the edged system. Furthermore, we propose an experimental scheme to detect the emergence of the chiral gapless edge state and distinguish different chiral topological orders by measuring the thermal conductance.

cond-mat.mes-hall↗

arXiv2010

First-principles study of ground state properties of zirconium dihydride

Structural, mechanical, electronic, and thermodynamic properties of fluorite and tetragonal phases of ZrH$_{2}$ are systematically studied by employing the density functional theory within generalized gradient approximation. The existence of the bistable structure for ZrH$_{2}$ is mainly due to the tetragonal distortions. And our calculated lattice constants for the stable face-centered tetragonal (fct) phase with \emph{c/a}=0.885 are consistent well with experiments. Through calculating elastic constants, the mechanically unstable characters of face-centered cubic (fcc) phase and fct structure with \emph{c/a}=1.111 are predicted. As for fct0.885 structure, our calculated elastic constants explicitly indicate that it is mechanically stable. Elastic moduli, Poisson's ratio, and Debye temperature are derived from elastic constants. After analyzing total and partial densities of states and valence electron charge distribution, we conclude that the Zr$-$H bonds in ZrH$_{2}$ exhibit weak covalent feature. But the ionic property is evident with about 1.5 electrons transferring from each Zr atom to H. Phonon spectrum results indicate that fct0.885 and fct1.111 structures are dynamically stable, while the fcc structure is unstable.

cond-mat.mtrl-sci↗

arXiv2010

First-principles calculations of phase transition, low elastic modulus, and superconductivity for zirconium

The elasticity, dynamic properties, and superconductivity of $α$, $ω$, and $β$ Zr are investigated by using first-principles methods. Our calculated elastic constants, elastic moduli, and Debye temperatures of $α$ and $ω$ phases are in excellent agreement with experiments. Electron-phonon coupling constant $λ$ and electronic density of states at the Fermi level $N$(\emph{E}$_{\rm{F}}$) are found to increase with pressure for these two hexagonal structures. For cubic $β$ phase, the critical pressure for mechanical stability is predicted to be 3.13 GPa and at \emph{P}=4 GPa the low elastic modulus ($E$=31.97 GPa) can be obtained. Besides, the critical pressure for dynamic stability of $β$ phase is achieved by phonon dispersion calculations to be $\mathtt{\sim}$26 GPa. Over this pressure, $λ$ and $N$(\emph{E}$_{\rm{F}}$) of $β$ phase decrease upon further compression. Our calculations show that the large value of superconducting transition temperature $\emph{T}_{\rm{c}}$ at 30 GPa for $β$ Zr is mainly due to the TA1 soft mode. Under further compression, the soft vibrational mode will gradually fade away.

cond-mat.mtrl-sci↗

arXiv2010

Thermophysical properties of liquid carbon dioxide under shock compressions: Quantum molecular dynamic simulations

Quantum molecular dynamic simulations are introduced to study the dynamical, electrical, and optical properties of carbon dioxide under dynamic compressions. The principal Hugoniot derived from the calculated equation of states is demonstrated to be well accordant with experimental results. Molecular dissociation and recombination are investigated through pair correlation functions, and decomposition of carbon dioxide is found to be between 40 and 50 GPa along the Hugoniot, where nonmetal-metal transition is observed. In addition, the optical properties of shock compressed carbon dioxide are also theoretically predicted along the Hugoniot.

cond-mat.mtrl-sci↗

arXiv2010

Structural, electronic, and thermodynamic properties of UN: Systematic density functional calculations

A systematic first-principle study is performed to calculate the lattice parameters, electronic structure, and thermodynamic properties of UN using the local-density approximation (LDA)+\emph{U} and the generalized gradient approximation (GGA)+\emph{U} formalisms. To properly describe the strong correlation in the U $5f$ electrons, we optimized the \emph{U} parameter in calculating the total energy, lattice parameters, and bulk modulus at the nonmagnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) configurations. Our results show that by choosing the Hubbard \emph{U} around 2 eV within the GGA+\emph{U} approach, it is promising to correctly and consistently describe the above mentioned properties of UN. The localization behavior of 5$f$ electrons is found to be stronger than that of UC and our electronic analysis indicates that the effective charge of UN can be represented as U$^{1.71+}$N$^{1.71-}$. As for the thermodynamic study, the phonon dispersion illustrates the stability of UN and we further predict the lattice vibration energy, thermal expansion, and specific heat by utilizing the quasiharmonic approximation. Our calculated specific heat is well consistent with experiments.

cond-mat.mtrl-sci↗

arXiv2010

Equation of state for shock compressed xenon in the ionization regime: ab initio study

Quantum molecular dynamic (QMD) simulations have been applied to study the thermophysical properties of liquid xenon under dynamic compressions. The equation of state (EOS) obtained from QMD calculations are corrected according to Saha equation, and contributions from atomic ionization, which are of predominance in determining the EOS at high temperature and pressure, are considered. For the pressures below 160 GPa, the necessity in accounting for the atomic ionization has been demonstrated by the Hugoniot curve, which shows excellent agreement with previous experimental measurements, and three levels of ionization have been proved to be sufficient at this stage.

cond-mat.mtrl-sci↗

arXiv2010

Magnetic coupling properties of rare-earth metals (Gd, Nd) doped ZnO: first-principles calculations

The electronic structure and magnetic coupling properties of rare-earth metals (Gd, Nd) doped ZnO have been investigated using first-principles methods. We show that the magnetic coupling between Gd or Nd ions in the nearest neighbor sites is ferromagnetic. The stability of the ferromagnetic coupling between Gd ions can be enhanced by appropriate electron doping into ZnO:Gd system and the room-temperature ferromagnetism can be achieved. However, for ZnO:Nd system, the ferromagnetism between Nd ions can be enhanced by appropriate holes doping into the sample. The room-temperature ferromagnetism can also be achieved in the \emph{n}-conducting ZnO:Nd sample. Our calculated results are in good agreement with the conclusions of the recent experiments. The effect of native defects (V$_{\rm{Zn}}$, V$_{\rm{O}}$) on the ferromagnetism is also discussed.

cond-mat.mtrl-sci↗

arXiv2010

Shock Wave Response of Porous Materials: From Plasticity to Elasticity

Shock wave reaction results in various characteristic regimes in porous material. The geometrical and topological properties of these regimes are highly concerned in practical applications. Via the morphological analysis to characteristic regimes with high temperature, we investigate the thermodynamics of shocked porous materials whose mechanical properties cover a wide range from hyperplasticity to elasticity. It is found that, under fixed shock strength, the total fractional area $A$ of the high-temperature regimes with $T \geq T_{th}$ and its saturation value first increase, then decrease with the increasing of the initial yield $σ_{Y0}$, where $T_{th}$ is a given threshold value of temperature $T$. In the shock-loading procedure, the fractional area $A(t)$ may show the same behavior if $T_{th}$ and $σ_{Y0}$ are chosen appropriately. Under the same $A(t)$ behavior, $T_{th}$ first increases then decreases with $σ_{Y0}$. At the maximum point $σ_{Y0M}$, the shock wave contributes the maximum plastic work. Around $σ_{Y0M}$, two materials with different mechanical properties may share the same $A(t)$ behavior even for the same $T_{th}$. The characteristic regimes in the material with the larger $σ_{Y0}$ are more dispersed.

cond-mat.mtrl-sci↗

arXiv2010

Exciton condensation and fractional charge in a bilayer two-dimension electron gas adjacent to a superconductor film

We study the exciton condensate (EC) in a bilayer two-dimension-electron-gas (2DEG) adjacent to a type-II superconductor thin film with an array of pinned vortex lattices. By applying continuum low energy theory and carrying numerical simulations of lattice model within mean-field approximation, we find that if the order parameter of EC has a vortex profile, there are exact zero modes and associated \emph{rational} fractional charge for zero pseudospin potential ($μ$) and average chemical potential ($h$): $μ$=0 and $h$=0; while for $μ\mathtt{\neq}0$ and $h$=0, intervalley mixing splits the zero energy levels, and the system exhibits \emph{irrational} fractional \emph{axial} charge.

cond-mat.mes-hall↗