The chemical potential of a component i in solution, µ i , has an ideal and and excess component: where q i is the internal partition function of a single molecule of the solute, U(N i ) is the potential energy of the system with N i particles, Λ is the de Broglie thermal wavelength, and V is the system's volume . 〈〉 ini t ial means that the term was obtained from an ensemble average over the configurations of the initial state (see Eq. 5). The first two terms of the equation above correspond to the ideal component of µ i ; the last one, µ ex i , corresponds to the excess component of µ i , and is associated with all non-ideal interactions of the extra component i with the solution (i.e. physical interactions that differ from those given by the ideal gas law). We obtained excess chemical potentials from solvation free energy calculations; the solute molecule is inserted in the solution by progressively turning on its interactions with the surrounding environment .