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The continuum (field theoretic) method has become the method of choice for multiscale structure-formation modeling of very different phase transformations in the past decade. One of the challenges in application of the method to transformations in real materials is to obtain the mesoscopic parameters, which characterize the thermodynamic system of interest. Significant progress has been made in the case of pure systems; however, one would like to know what changes need to be made in the case of binary or multicomponent systems. We consider an exactly solvable case of the linear multicomponent system undergoing a phase transformation and derive equations that relate parameters of the continuum method, like barrier height, gradient energy, and relaxation coefficients, to the measurable quantities, like interface energy, interfacial thickness, and kinetic coefficient. We find that the contribution of chemical interactions in the system can be expressed as the renormalization of the barrier-height parameter of the continuum method and replacement of the latent heat with the chemical modulus. Atomic-scale simulations data for a solid/liquid transition in a binary Cu-Ni system were chosen for comparison with the theory and the fitting yields the estimates for the continuum-method parameters. Analysis of the temperature dependence of the interfacial energy allowed us to shed light on the magnitudes of the internal energy and entropy contributions into the solid/liquid interface.