  We describe in detail a recently proposed lattice-Boltzmann model for
simulating flows with multiple phases and components. In particular, the focus
is on the modeling of one-component fluid systems which obey non-ideal gas
equations of state and can undergo a liquid-gas type phase transition. The
model is shown to be momentum-conserving. From the microscopic mechanical
stability condition, the densities in bulk liquid and gas phases are obtained
as functions of a temperature-like parameter. Comparisons with the
thermodynamic theory of phase transition show that the LBE model can be made to
correspond exactly to an isothermal process. The density profile in the
liquid-gas interface is also obtained as function of the temperature-like
parameter and is shown to be isotropic. The surface tension, which can be
changed independently, is calculated. The analytical conclusions are verified
by numerical simulations. (To appear in Phys. Rev. E)
