Nonperturbative density-functional theories of classical nonuniform systems

We propose an approximation to the density-functional theory of classical nonuniform systems that reproduces all the formal properties of the free energy and requires only the direct correlation function of the uniform system as input. By introducing additional assumptions into this theory a direct relation can be established with most of the existing nonperturbative theories. When the theory is worked out for the case of the hard-sphere solid, very good agreement is found with the computer simulations. The free energies, pressures, and fluid-solid coexistence data are reproduced to within the error bars of the simulations. The theory also predicts stable bcc and sc phases that could play a role in the final nucleation of the equilibrium fcc phase.