SCM: ADF COSMO-RS 98

Combinatorial term

In Ref.[2] a thermodynamically inconsistent combinatorial contribution μ_i^comb to the chemical potential was used:

μ_i^comb	=	- λRT ln (q_av/Angstrom²)
q_av	=	∑_i x_i q_i

In this equation q_i is the surface area of the molecular volume of compound i, x_i is the molar fraction of compound i in the solution, and λ is a COSMO-RS parameter.

The importance of using a thermodynamically consistent combinatorial contribution is discussed in Ref. [3]. In the ADF COSMO-RS program it is possible to use a thermodynamically consistent combinatorial contribution of the form (Equation C.4 of Ref.[3], with λ₀=λ₁=λ₂=λ):

μ_i^comb	=	λRT (1 - r_i/r_av + ln(r_i/r_av) + 1 - q_i/q_av - ln (q_av/Angstrom²))
r_av	=	∑_i x_i r_i

In this equation r_i is the molecular volume of compound i. In the ADF COSMO-RS program this combinatorial term is used by default, see also Ref. [4].