G. E. Norman

Standards for molecular dynamics modelling and simulation of relaxation

An attempt is made to formulate a set of requirements for simulation and modelling of relaxation in dense media. Each requirement is illustrated by examples of numerical simulation of particles with different types of interaction given by soft-sphere, Lennard–Jones, embedded atom method or Coulomb potential. The approaches developed are expected to be universal for some classes of relaxation processes in liquids, fluids, crystals and plasmas.

Laser ablation of gold: Experiment and atomistic simulation

The interaction of radiation of a picosecond X-ray laser (wavelength λ = 13.9 nm) with targets made of a thick gold film has been studied theoretically and experimentally. It has been shown experimentally that the action of individual X-ray laser pulses with a fluence of F ≈ 21 mJ/cm2 initiates the nanostructuring of the gold surface. Explicitly taking into account the electron subsystem, we have proposed an atomistic model of ablation that makes it possible to adequately describe the experimental results. The atomistic simulation involves the ion-ion potential depending on the electron temperature Te. The use of such a potential makes it possible to take into account an increase in the pressure in the system with increasing Te and to reveal two laser ablation mechanisms.

Stochastic and dynamic properties of molecular dynamics systems: Simple liquids, plasma and electrolytes, polymers

Abstract The concept of dynamical memory time t m is discussed. The relation between t m , fluctuation of energy ΔE and K -entropy (Lyapunov exponent) is treated. The meaning of t m for real systems is related to the thermal and Langevin noise and quantum uncertainty. Relaxation of kinetic energy to equilibrium state was studied by MDM for non-equilibrium strongly coupled plasmas. Violation of the microscopic reversibility principle in some enzymatic reactions is discussed.

Superheating of solid metal prior to electric explosion of wires at fast energy deposition

We develop the concept which distinguishes the initial stages of the fast (nanosecond) electric explosion of wires: the superheating of the solid conductor, its spontaneous (spinodal) decay and the successive formation of the non-ideal plasma column. We use the molecular dynamics simulation approach to simulate homogeneous nucleation from a stationary state and at a constant heating rate. We study the parameters of the spinodal, the dependence of the melting temperature on the heating rate and the character of the decay. We consider the subsequent evolution of the fluid column and the axial plasma uniformity. We compare the results with the experimental data on nanosecond wire explosions.

Nonideal plasmas as non-equilibrium media

Various aspects of the collective behaviour of non-equilibrium nonideal plasmas are studied. The relaxation of kinetic energy to the equilibrium state is simulated by the molecular dynamics (MD) method for two-component non-degenerate strongly non-equilibrium plasmas. The initial non-exponential stage, its duration and the subsequent exponential stage of the relaxation process are studied for a wide range of ion charge, nonideality parameter and ion mass. A simulation model of the nonideal plasma excited by an electron beam is proposed. An approach is developed to calculate the dynamic structure factor in non-stationary conditions. Instability increment is obtained from MD simulations.

Nonequilibrium nonideal nanoplasma generated by a fast single ion in condensed matter

A plasma model of relaxation of a medium in heavy ion tracks in condensed matter is proposed. The model is based on three assumptions: the Maxwell distribution of plasma electrons, localization of plasma inside the track nanochannel and constant values of the plasma electron density and temperature during the x-ray irradiation. It is demonstrated that the plasma relaxation model adequately describes the x-ray spectra observed upon interaction of a fast ion with condensed target. Assumptions of plasma relaxation model are validated by the molecular dynamics modeling and simulation.

Nonequilibrium Nonideal Nanoplasma Generated by a Fast Single Ion in Condensed Matter

A plasma model of relaxation of a medium in heavy ion tracks in condensed matter is proposed. The model is based on three assumptions: the Maxwell distribution of plasma electrons, localization of plasma inside the track nanochannel and constant values of the plasma electron density and temperature during the X‐ray irradiation. It is demonstrated that the plasma relaxation model adequately describes the X‐ray spectra observed upon interaction of a fast ion with condensed target. Preassumptions of plasma relaxation model are validated by the molecular dynamics modeling and simulation.

Dynamic and Stochastic Properties of Molecular Systems: From Simple Liquids to Enzymes

Molecular dynamics method (MDM) supplies to the solution of fundamental contradiction between macroscopic irreversibility and microscopic reversibility with data which help to reveal the origin of stochastization in many-particle systems. The relation between dynamic memory time tm, fluctuation of energy dE and K-entropy (Lyapunov exponent) is treated. MDM is a method which retains Newtonian dynamics only at the times less than tm and carries out a statistical averaging over initial conditions along the trajectory run. Meaning of tm for real systems is related to the quantum uncertainty, which is always finite for any classical system and influence upon particle trajectories in a coarse-graining manner. Relaxation of kinetic energy to equilibrium state was studied by MDM for non-equilibrium strongly coupled plasmas. Two stages of relaxation were observed: initial fast non-Boltzmann oscillatory stage and further relatively slow Boltzmann relaxation. Violation of the microscopic reversibility principle in some enzymatic reactions is discussed.

The Second Law and Karl R. Popper

Popper’s ideas are briefly presented on philosophy of Science hierarchy of particular sciences and his emergence principle. Main points of Popper’s cognition theory are emphasized. Popper’s thoughts are given in connection with struggle of scientific ideas in the XX century. The projection on the Second Law is done.