Dynamical Ionic Clusters with Flowing Electron Bubbles from Warm to Hot Dense Iron along the Hugoniot Curve (original) (raw)
Related papers
Physical Review Letters, 2012
The complex structures of warm and hot dense matter are essential to understand the behaviors of materials in high energy density physics processes and provide new features of matter constitutions. Here, along a new unified first-principle determined Hugoniot curve of iron from normal condensed condition up to 1 Gbar, the novel structures characterized by the ionic clusters and separated "electron bubbles" are revolutionarily unraveled using newly developed quantum Langevin molecular dynamics (QLMD). Subsistence of complex clusters, with bonds formed by inner shell electrons of neighbor ions, can persist in the time length of 50 femto-seconds dynamically with quantum flowing bubbles, which are produced by the interplay of Fermi electron degeneracy, the ionic coupling and the dynamical nature. With the inclusion of those complicated features in QLMD, the present data could serve as a first-principle benchmark in a wide range of temperatures and densities.
A new determined principal Hugoniot curve of Fe in the temperature range of 0.1-100 eV from Ab initio is presented, and the structural dynamics along this curve is shown. All experiments are on top or above our Hugoniot data, which are along the lower envelop of the distribution of experiments. The present data are the converged limit for experiments to remove the external effects such as preheating. In particular, the experimental data on the bottom of the distribution below 10 Mbar can be considered nearly free of errors caused by the external effects compared with our data. The dynamics of ionic structures shows the stable existence of complex clusters with persisted time length of hundreds of femto-seconds from cold to hot dense matter.
Stability of helium bubbles in alpha-iron: A molecular dynamics study
Journal of Nuclear Materials, 2009
Molecular dynamics simulations were performed to estimate the dissociation energies of helium interstitials, vacancies and self-interstitial atoms from small helium-vacancy clusters. Several sets of empirical potentials have been tested and compared with available ab initio calculations in order to provide the best combination of potentials to study the stability of small helium bubbles. The behavior of the cluster seems to be better described using Ackland potential for the Fe-Fe interactions and Juslin potential for the Fe-He interactions. From the calculations, it appears that the dissociation energies mainly depend on the helium-to-vacancy ratio rather than the cluster size. The helium/vacancy crossover slightly varies with increasing number of vacancies, but the crossover defining the loop-punching regime decreases strongly with increasing cluster sizes.
Journal of Alloys and Compounds, 2005
Stable structures and energetics of iron clusters, Fen (n up to 36), have been investigated by performing molecular dynamics simulations. A Lennard–Jones type pair-potential energy function recently proposed for iron crystal studies [Mohri et al., J. Alloys Compd. 317 (2001) 13] has been used to describe the particle interactions in the simulations. The growing pattern of iron clusters is analyzed via rearrangement collision. The general trends in this pattern are discussed by comparing with recent quantum calculations. Finally, a preferable growth mechanism for Fen clusters is determined.
Semi-classical description of ionic and electronic dynamics in metal clusters
Annalen der Physik, 2002
We present a selfconsistent semi-classical description of metal clusters with explicit ionic background. We show in particular how the flexibility of the Husimi picture allows a proper, self contained, description of ground state as well as dynamical properties of metal clusters. This leads to a coupled electrons + ions molecular dynamics, which may be followed over long times (typically one picosecond). We consider real time dynamics for electrons at a Vlasov-LDA level and include dynamical correlations by an Ûhling-Uhlenbeck collision term (VUU). We discuss the effect of the Husimi representation on the electronic dynamics and the impact of a constant isotropic differential cross-section in the UU collision term, as compared to a velocity dependent anisotropic differential cross section. Finally, we show that the VUU approach is capable of curing the artificial dissipation of an initial fermionic distribution function towards a classical Boltzmann equilibrium over long times.
Warm dense matter through classical molecular dynamics
High Energy Density Physics, 2014
A classical Molecular Dynamics code has been developed to simulate dense plasmas i.e. neutral systems of interacting ions and electrons. Our goal is to design a tool that relies on a reduced set of microscopic mechanisms in order to obtain solutions of complex time dependent n-body problems and to allow an efficient description of the plasma states between classical high temperature systems to strongly coupled plasmas. Our present objective is an attempt to explore the behavior of such a classical approach for typical conditions of warm dense matter. We calculate the dynamic structure factor in warm dense beryllium by means of our molecular dynamics simulations. The results are then compared with those obtained within the framework of the random phase approximation (RPA).
Thermodynamics of Atomic Clusters Using Variational Quantum Hydrodynamics †
The Journal of Physical Chemistry A, 2007
Small clusters of rare-gas atoms are ideal test cases for studying how quantum delocalization affects both the thermodynamics and the structure of molecular scale systems. In this paper, we use a variational quantum hydrodynamic approach to examine the structure and dynamics of (Ne) n clusters, with n up to 100 atoms, at both T ) 0 K and for temperatures spanning the solid-to-liquid transition in bulk Ne. Finite temperature contributions are introduced to the grand potential in the form of an "entropy" potential. One surprising result is the prediction of a negative heat capacity for very small clusters that we attribute to the nonadditive nature of the total free-energy for very small systems.
Electron bubbles in helium clusters. I. Structure and energetics
Chemical Physics, 2006
In this paper we present a theoretical study of the structure, energetics, potential energy surfaces, and energetic stability of excess electron bubbles in (He4)N (N=6500-106) clusters. The subsystem of the helium atoms was treated by the density functional method. The density profile was specified by a void (i.e., an empty bubble) at the cluster center, a rising profile towards a constant interior value (described by a power exponential), and a decreasing profile near the cluster surface (described in terms of a Gudermannian function). The cluster surface density profile width (˜6Å) weakly depends on the bubble radius Rb, while the interior surface profile widths (˜4-8Å) increase with increasing Rb. The cluster deformation energy Ed accompanying the bubble formation originates from the bubble surface energy, the exterior cluster surface energy change, and the energy increase due to intracluster density changes, with the latter term providing the dominant contribution for N =6500-2×105. The excess electron energy Ee was calculated at a fixed nuclear configuration using a pseudopotential method, with an effective (nonlocal) potential, which incorporates repulsion and polarization effects. Concurrently, the energy V0 of the quasi-free-electron within the deformed cluster was calculated. The total electron bubble energies Et=Ee+Ed, which represent the energetic configurational diagrams of Et vs Rb (at fixed N), provide the equilibrium bubble radii Rbc and the corresponding total equilibrium energies Ete, with Ete(Re) decreasing (increasing) with increasing N (i.e., at N =6500, Re=13.5Å and Ete=0.86eV, while at N =1.8×105, Re=16.6Å and Ete=0.39eV). The cluster size dependence of the energy gap (V0-Ete) allows for the estimate of the minimal (He4)N cluster size of N ≃5200 for which the electron bubble is energetically stable.