Analysis of phase transitions in two-dimensional Coulomb clusters by the dynamic entropy method

The dynamics of two-dimensional clusters consisting of 7 and 18 particles whose interaction is described by a screened Coulomb potential has been numerically simulated by the Langevin molecular dynamics method. With the use of the data obtained for the displacements and velocities of particles, the functions of the “mean first-passage time” dynamic entropy have been obtained for clusters having different kinetic temperatures close to the conditions of laboratory experiments with macroparticles in a gas-discharge plasma. Three phase states of the small systems under consideration—crystal, liquid, and transient—have been observed. A mechanism of phase transitions under consideration has been described. The method proposed to analyze the dynamics of systems can be used for extremely small structures.