We introduce here the Fourier correlation (FC) method for obtaining bulk diffusion coefficients in simulations of condensed, nonideal mixtures. The method in particular allows a Fickian mutual diffusion coefficient to be calculated directly in a molecular dynamics simulation and provides for a correction of errors due to finite system sizes. It is an equilibrium method that may be performed at the same time as standard thermodynamic computations. The method is tested by simulating a binary system of LJ particles meant to approximate a nonideal liquid mixture of methane and carbon tetrafluoride. Results are validated by comparison to Green-Kubo and nonequilibrium methods and simulation at multiple system sizes.