Charge Correlations in a Harmonic Trap
  A system of N classical Coulomb charges trapped in a harmonic potential displays shell structure and orientational ordering. The local density profile is well understood from theory, simulation, and experiment. Here, pair correlations are considered for this highly inhomogeneous system for both the fluid and ordered states. In the former, it is noted that there is a close relationship to pair correlations in the uniform OCP. For the ordered state, it is shown that the disordered "tiling" is closely related to the ground state Thomson sites for a single sphere. 
Jeffrey Wrighton, Hanno K\"ahlert, Torben Ott, Patrick Ludwig, Hauke   Thomsen, James Dufty, Michael Bonitz
cond-mat.stat-mech