Warm dense matter conductivity and reflectivity are investigated by means of density functional theory. Both one- and two-temperature cases are considered. One-temperature mode is related to equilibrium state where temperature of electrons and ions are equal. As an example of one-temperature system xenon plasma is studied. The reflectivity of shock-compressed dense xenon plasma is calculated and compared with experimental data. Two-temperature mode is associated with different temperature of electrons and ions. The thermal conductivity of aluminum and gold in such mode is examined. The comparison of obtained results with theoretical model based on Boltzmann equation is conducted.
The method ofWave Packet Molecular Dynamics Method (WPMD) is a promising replacement of the classical molecular dynamics for the simulations of many-electron systems including nonideal plasmas. In this contribution we report on a packet splitting technique where an electron is represented by multiple Gaussians, with mixing coefficients playing the role of additional dynamic variables. It provides larger flexibility and better accuracy than the original WPMD with a single Gaussian per electron. As a test case we consider ionization of hydrogen atom in a short laser pulse, where the split packets provide a basis for quantum branching.
Warm dense hydrogen is studied in the region of fluid–fluid phase transition within the framework of the density functional theory. We report a procedure of obtaining metastable states and calculate the equation of state. Metastable states are diagnosed by pair correlation functions and values of conductivity. We obtain a strong overlapping through the density of metastable and equilibrium branches of pressure isotherms. This indicates the plasma nature of the phase transition
At first, we present a brief review of the problem. Then, we consider plasma phase transition (PPT) as a mechanism of the first order fluid–fluid phase transition in warm dense hydrogen. The pros and cons are analysed. The properties of warm dense hydrogen are investigated by ab initio methods of molecular dynamics using the density functional theory. Strong ionization during the fluid–fluid phase transition in warm dense hydrogen makes this transition close to the prediction of the PPT. Finally, we present differences in the real phase transition from the prediction 1968–1969. Structures are observed with inter‐proton separations that are equal to the distances between protons in the and ions. The transition is not only ionization, but also structural. An analysis of the phase transition counterpart in solid hydrogen under high pressure allows us to reveal partially the character of the new structure. The ionized phase includes complex cluster ions. Van der Waals loops are of abnormal inverted form.
A new idea is developed that the fluid–fluid phase transition in warm dense hydrogen is related to the partial ionization of molecular hydrogen H2 with formation of molecular ions H+2 and H+3 . Conventional ab initio quantum modelling is applied. The proton–proton pair correlation functions (PCFs) obtained are used for the non-conventional diagnostics of the phase transition and elucidation of its nature for temperatures in the range 700–1500 K. Short- and long-range changes of PCFs are studied. Ionization of H2 molecules and the appearance of molecular ions H+2and H+3 are revealed. The validity of the soft sphere model is tested for the long-range order.
Ab initio quantum modeling is applied to check the ideas that motivated studies of both plasma phase transition (PPT) and Brazhkin semiconductor-to-metal phase transition, and to analyze both similarity and difference between them as well as with the Wigner metallization. Electron density of states and the characteristic gap in it are investigated to verify the semiconductor-to-metal nature of the transition. The change of plasma frequency is suggested to be used instead of the “degree of ionization” to characterize the difference between two plasma phases at PPT. Electron density of states, pair distribution function, and conductivity are calculated as well. It is shown that Norman-Starostin ideas about (a) PPT and (b) phase diagram for fluids are not anymore a hypothesis. They are confirmed by the experimental data.
Non-equilibrium two-temperature warm dense metals consist of the ion subsystem that is subjected to structural transitions and involved in the mass transfer, and the electron subsystem that in various pulsed experiments absorbs energy and then evolves together with ions to equilibrium. Definition of pressure in such non-equilibrium systems causes certain controversy. In this work we make an attempt to clarify this definition that is vital for proper description of the whole relaxation process. Using the density functional theory we analyze on examples of Al and Au electronic pressure components in warm dense metals. Appealing to the Fermi gas model we elucidate a way to find a number of free delocalized electrons in warm dense metals.
The influence of boundary conditions for the classical and wave packet molecular dynamics (MD) simulations of nonideal electron-ion plasma is studied. We start with the classical MD and perform a comprehensive study of convergence of the per-particle potential energy and pressure with the number of particles using both the nearest image method (periodic boundaries) and harmonic reflective boundaries. As a result an error caused by finiteness of the simulation box is estimated. Moreover electron oscillations given by the spectra of the current autocorrelation function are analyzed for both types of the boundary conditions. A special attention is paid to the reflecting boundaries since they prevent wave packet spreading in the Wave Packet MD. To speed up classical MD simulations we use the GPU-accelerated code.