and M * is the adjoint of M. Due to the role of Ψ in eq. 9, we will refer to it also as "adjoint RHS". For the three models, the RHS F is written as the product of a term which is specific to the solute and a term which is merely geometric. This allows the factorization (due to the product rule) of its derivative in a term that does not depend on the nature of the solute and a term that has different expressions depending on the nature of ρ. Hence the derivative is written as F λ = F λ solvent + F λ solute , and we can further write E λ s as