Ground states of model core-softened colloids

We numerically study the condensed phases of repelling core-softened spheres confined to a planar cell at the crossover from two to three dimensions. In the related experiment presented in Osterman et al (2007 Phys. Rev. Lett.99 248301) the dipolar interaction between superparamagnetic spheres trapped in a thin cell was induced by a transverse magnetic field and tuned by adjusting the cell thickness. Depending on the cell thickness, the interaction can be purely repulsive (2D dipole‐dipole), softened repulsive, or attractive at small distances. Clustering of colloids without any attractive force has been observed. Here we analyze the observed mesophases numerically by means of Monte Carlo simulations and by genetic algorithms based energy optimization. We observe the same phases seen in the experiment including expanded hexagonal, square, chain-like, stripe/labyrinthine, and honeycomb structures.