COSMOSPACE is an activity coefficient

Activity coefficient

An activity coefficient is a factor used in thermodynamics to account for deviations from ideal behaviour in a mixture of chemical substances. In an ideal mixture, the interactions between each pair of chemical species are the same and, as a result, properties of the mixtures can be expressed...

 model in which the activity coefficient of the components in a
liquid chemical mixture can be related through their molar fraction.

While UNIQUAC

UNIQUAC

UNIQUAC is an activity coefficient model used in description of phase equilibria.The model is a so-called lattice model and has been derived from a first order approximation...

 is a first order approximation

Orders of approximation

In science, engineering, and other quantitative disciplines, orders of approximation refer to formal or informal terms for how precise an approximation is, and to indicate progressively more refined approximations: in increasing order of precision, a zeroth order approximation, a first order...

, COSMOSPACE gives the exact solution of a lattice model in which pairwise molecule surfaces interact. Therefore COSMOSPACE outperforms Uniquac in the description of vapor-liquid and liquid-liquid phase equilibria.