Lingcang Cai

First-principles investigations of elastic stability and electronic structure of cubic platinum carbide under pressure

[Sun, Xiao-Wei; Chen, Qi-Feng; Cai, Ling-Cang; Jing, Fu-Qian] China Acad Engn Phys, Natl Key Lab Shock Wave & Detonat Phys, Inst Fluid Phys, Mianyang 621900, Peoples R China. [Sun, Xiao-Wei; Chen, Xiang-Rong; Jing, Fu-Qian] Sichuan Univ, Inst Atom & Mol Phys, Sch Phys Sci & Technol, Chengdu 610065, Peoples R China. [Sun, Xiao-Wei] Lanzhou Jiaotong Univ, Sch Math & Phys, Lanzhou 730070, Peoples R China. [Chen, Xiang-Rong] Chinese Acad Sci, Int Ctr Mat Phys, Shenyang 110016, Peoples R China.;Sun, XW (reprint author), China Acad Engn Phys, Natl Key Lab Shock Wave & Detonat Phys, Inst Fluid Phys, Mianyang 621900, Peoples R China;sunxw_lzjtu@126.com chen_qifeng@iapcm.ac.cn xrchen@126.com

Self-consistent variational calculation of the dense fluid helium in the region of partial ionization

Developments in shock-wave experimental techniques have allowed Megabar pressure range in dense fluid to be probed. It has been shown that the dissociation of the molecule and ionization of the atom become operative under such ultrahigh pressures. The dense fluid helium will be ionized in high pressures and temperatures. The ionization energy of helium will be lowered due to the interactions among all particles of He, He+, He2+, and e. The ionization degree is obtained from nonideal ionization equilibrium, taking into account the correlation contributions to the chemical potential which is determined self-consistently by the free energy function. The composition of dense helium can be calculated with given densities and temperatures. The equations of state of dense helium plasma are predicted in the density and temperature range of 0

Multishock comparison of dense gaseous H2+He mixtures up to 30 GPa

Time-resolved spectral radiation histories of the gaseous H(2) + He mixtures under shock loadings were measured by using a six-wavelength channel pyrometer. The initial gaseous mixtures had a mole component of H(2):He = 1:1.21, which were shocked from room temperature and initial pressure of 20 MPa to a pressure range of 1-30 GPa and temperature range of 3000-7000 K by means of a two-stage light-gas gun. Multishock reverberations between the base-plate and sapphire window can be observed up to the fifth-shock compressions. The experimental data are in good agreement with self-consistent fluid variational theory calculations in which the dissociation process of hydrogen molecules and various interactions among atomic and molecular species are taken into account.

The dissociation and equation of state of dense fluid oxygen at high pressures and high temperatures

The dissociation, pressure, and internal energy of dense fluid oxygen at high temperatures and densities have been calculated from the free-energy functions using the self-consistent fluid variational theory. In this paper, we focused on a mixture of oxygen atoms and molecules, and investigated the phenomenon of pressure dissociation at finite temperature. The single-shock Hugoniot derived from this equation of state agrees well with gas-gun experiments for pressure versus density. The equation of state and dissociation degree are predicted in the ranges of temperature of 5000-16,000 K and density of 0.1-4.5 g/cm(3). These data are formulated in the analytical forms of dissociation degree-density-temperature and pressure-density-temperature equation of state.

Thermophysical properties of multi-shock compressed dense argon.

In contrast to the single shock compression state that can be obtained directly via experimental measurements, the multi-shock compression states, however, have to be calculated with the aid of theoretical models. In order to determine experimentally the multiple shock states, a diagnostic approach with the Doppler pins system (DPS) and the pyrometer was used to probe multiple shocks in dense argon plasmas. Plasma was generated by a shock reverberation technique. The shock was produced using the flyer plate impact accelerated up to ∼6.1 km/s by a two-stage light gas gun and introduced into the plenum argon gas sample, which was pre-compressed from the environmental pressure to about 20 MPa. The time-resolved optical radiation histories were determined using a multi-wavelength channel optical transience radiance pyrometer. Simultaneously, the particle velocity profiles of the LiF window was measured with multi-DPS. The states of multi-shock compression argon plasma were determined from the measured shock velocities combining the particle velocity profiles. We performed the experiments on dense argon plasmas to determine the principal Hugonoit up to 21 GPa, the re-shock pressure up to 73 GPa, and the maximum measure pressure of the fourth shock up to 158 GPa. The results are used to validate the existing self-consistent variational theory model in the partial ionization region and create new theoretical models.

Self-consistent fluid variational theory for the dissociation of dense nitrogen.

The self-consistent fluid variational theory is used to calculate the pressure dissociation of dense nitrogen at high temperatures. The accurate high-pressure and high-temperature effective pair potentials are adopted to describe the intermolecular interactions, which are made to consider molecular dissociation. This paper focuses on a mixture of nitrogen atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperature. The equation of state and dissociation degree are calculated from the free-energy functions in the range of temperature of 2000-15 000 K and density of 0.2-3.0 gcm(3), which can be compared with other approaches and experiments.

The equation of state, shock-induced molecule dissociation, and transparency loss for multi-compressed dense gaseous H2 + D2 mixtures

The experimental equation of state and temperature data of the dense gaseous H2 + D2 mixtures under multi-shock compression were presented in a pressure range of 2–36 GPa and a temperature range of 2300–5300 K. The strong shock wave was produced using the flyer plate impact by accelerated up to 5.1–6.2 km/s with a two-stage light-gas gun and introduced into the plenum gas sample, which was pre-compressed from environmental pressure to 30–40 MPa. Time-resolved spectral radiation histories were acquired with two sets of multi-wavelength channel pyrometers, which were used to determine the shock velocity and shock temperature in the sample. Shock pressure and particle velocity were obtained by the impedance matching method. The experimental data prove the validity of self-consistent fluid variational theory (SFVT) model in the partial dissociation region. The time-resolved spectral radiation histories along with the SFVT calculation show that the shocked gas samples lose their transparency in visible light wavelength ranges of 400–800 nm at about 12.99 GPa and 4413 K or higher.

Equation of state of partially ionized argon plasma

The ionization degree, Hugoniots, and equation of state of partially ionized argon plasma were calculated by using self-consistent fluid variational theory for temperature of 6–50 kK and density of 0.05–4.0 g/cm3. The corrections of lowering of ionization energy of fluid argon caused by the interactions among all particles of Ar, Ar+, Ar2+, and e have been taken into consideration in terms of the correlation contributions to the chemical potential which is determined self-consistently by the free energy function. The initial density effects of gas argon under shock compression have been discussed. Comparison is performed with available shock-wave experiments and other theoretical calculations.

Self-consistent fluid variational theory for the equation of state and dissociation of dense hydrogen and nitrogen

The self-consistent fluid variational theory (SFVT) is used to calculate the pressure dissociation of dense hydrogen and nitrogen at high temperatures. The accurate high-pressure and high-temperature effective pair potentials are adopted to describe the intermolecular interactions, which are made to consider molecular dissociation. This paper focuses on a mixture of atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperature. The equation of state and dissociation degree are calculated from the free energy functions in the temperature range 4000-15 000 K and density range 0.1-3.2 g cm -3 for dense nitrogen and in the temperature range 2000- 10 000 K and density range 0.02-1.0 g cm -3 for dense hydrogen, which can be compared with other approaches and experiments. The pressure dissociation is found to occur in the higher density range, while temperature dissociation is a more gradual effect.

Theoretical calculation of the shock compression properties of liquid H2 + D2 mixtures

Based on liquid variational perturbation theory with quantum mechanics correction, the effective exp-6 potential is adopted to compute the shock Hugoniot of liquid H2 + D2 mixtures at different molar rations. An examination of the confidence of the above computation is performed by comparing experiments and calculations, in which similar calculation procedure used for H2 + D2 is adopted for H2 and D2 each, since no experimental data are available to conduct this kind of comparison. Good agreement in both comparisons is found. This fact may look as if an indirect positive verification of calculation procedure was used here at least in the pressure and temperature domain covered by the experimental data of H2 and D2 used for comparison, numerically nearly up to 20 GPa and 104 K.