Interpretation of the atomic formulae for stress and stiffness coefficients

Structural and elastic properties of a confined two-dimensional colloidal solid: a molecular dynamics study

We implement molecular dynamics simulations in canonical ensemble to study the effect of confinement on a two-dimensional crystal of point particles interacting with an inverse power law potential proportional to r^{-12} in a narrow channel. This system can describe colloidal particles at the air-water interface. It is shown that the system characteristics depend sensitively on the boundary conditions at the two walls providing the confinement. The walls exert perpendicular forces on their adjacent particles. The potential between walls and particles varies as the inverse power of ten. Structural quantities such as density profile, structure factor, and orientational order parameter are computed. It is shown that orientational order persists near the walls even at temperatures where the system in the bulk is in fluid state. The dependence of elastic constants, stress tensor elements, shear, and bulk moduli on density as well as the channel width is discussed. Moreover, the effect of channel incommensurability with the triangular lattice structure is discussed. It is shown that incommensurability notably affects the system properties. We compare our findings to those obtained by Monte Carlo simulations in Rici et al. [Phys. Rev. E 75, 011405 (2007)] and to the case with the periodic boundary condition along the channel width.