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A second-order density-functional theory is used to study the isotropic-nematic transition in a system of hard ellipsoids of revolution. The direct pair-correlation functions of the coexisting isotropic liquid that enter in the theory as input information are obtained from solving the Ornstein-Zernike equation using the Percus-Yevick closure relation. The spherical harmonic expansion coe%cients of the correla-

We propose a ''mixed'' integral equation for the pair correlation function of molecular fluids which interpolates between the hypernetted-chain and Percus-Yevick approximations. Thermodynamic consistency between the virial and compressibility equation of state is achieved by varying a single parameter in a suitably chosen mixing function. The integral equation proposed here generalizes the suggestion by Rogers and Young ͓Phys. Rev. A 30, 999 ͑1984͔͒ to an angle-dependent pair potential. When compared to available computer simulation data, the equation is found to yield excellent results for both the thermodynamic properties and the pair-correlation functions. ͓S1063-651X͑96͒02507-X͔ PACS number͑s͒: 61.20.Gy, 61.25.Em

We have used the density-functional theory to locate the freezing transitions and calculate the values of freezing parameters for a system of long elongated molecules which interact via the Gay-Berne pair potential. The pair correlation functions of isotropic phase which enter in the theory as input informations are found from the Percus-Yevick integral equation theory. At low temperatures the fluid freezes directly into the smectic A phase on increasing the density. The nematic phase is found to stabilize in between the isotropic and smectic A phases only at high temperatures and high densities. These features of the phase diagram are in good agreement with the computer simulation results.

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