  A new molecular simulation method for the calculation of vapour-liquid
equilibria of mixtures is presented. In this method, the independent
thermodynamic variables are temperature and liquid composition. In the first
step, one isobaric isothermal simulation for the liquid phase is performed, in
which the chemical potentials of all components and their derivatives with
respect to the pressure, i.e., the partial molar volumes, are calculated. From
these results, first order Taylor series expansions for the chemical potentials
as functions of the pressure $\mu_i(p)$ at constant liquid composition are
determined. That information is needed, as the specified pressure in the liquid
will generally not be equal to the equilibrium pressure, which has to be found
in the course of a vapour simulation. In the second step, one pseudo grand
canonical simulation for the vapour phase is performed, where the chemical
potentials are set according to the instantaneous pressure $p^v$ using the
previously determined function $\mu_i(p^v)$. In this way, results for the
vapour pressure and vapour composition are achieved which are consistent to the
given temperature and liquid composition.The new method is applied to the pure
Lennard-Jones fluid, a binary, and a ternary mixture of Lennard-Jones spheres
and shows very good agreement with corresponding data from the literature.
