Yukawa mixtures with and without gravity

The structures of systems of particles with repulsive Yukawa interactions a re analyzed by molecular dynamics simulations with emphasis on the behavior of Yukawa mixtures. To keep the density of particles with mutual repulsion at finite values, we need some confining mechanism and the latter has stro ng effects on the structure formation. Under the gravity, the confinement i s one-dimensional and we have layered structures. In this case, Yukawa mixt ures are separated by the difference in the charge to mass ratios. In the c ase without gravity, we may have three-dimensional confinement and the beha vior of the system may be analyzed by assuming spherical symmetry. We show that there also occurs a separation of species according to the magnitude o f charges under the condition of no gravity and we have well-organized stru ctures when the temperature is sufficiently low.