To obtain the true thermodynamic equilibrium of systems of anisotropic molecules is difficult because of the complicated potential lanscape. There is a high probability that simulated system may be caught in one of the many local minima. Especially, simulated systems of anisotropic molecules often yield anisotropic pressure under periodic boundary conditions. The situation is especially critical for high density phases such as crystal and smectic. We discuss how to simulate the thermodynamic equilibrium under hydrostatic pressure, and investigate the properties of crystal-smectic transition.