Two-dimensional Classical Wigner Crystal: Elliptical Confining Potential
  We investigate theoretically the ground-state configurations of two-dimensional charged-particle systems with an elliptical hard-wall boundary and their vibrational eigenmodes. The systems exhibit a series of structural transitions, finally changing from a zigzag structure to a one-dimensional Coulomb chain, as the eccentricity of the elliptical hard-wall boundary is increased. 
Zhen-zhong Zhang, Kai Chang