  Self-assembling novel ordered structures with nanoparticles has recently
received much attention. Here we use computer simulations to study a
two-dimensional model system characterized by a simple isotropic interaction
that could be realized with building blocks on the nanoscale. We find that the
particles arrange themselves into hexagonal superstructures of twin boundaries
whose superlattice vector can be tuned reversibly by changing the temperature.
Thermodynamic stability is confirmed by calculating the free energy with a
combination of thermodynamic integration and the Frenkel-Ladd method. Different
contributions to the free energy difference are discussed.
