Title: Primitive model electrolytes. A comparison of the HNC approximation for the activity coefficient with Monte Carlo data
Author(s):

	E. Gutiérrez-Valladares (Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, A.P. 1-1010, 76000 Querétaro, México, University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškerčeva c. 5, SI-1000 Ljubljana, Slovenia ),
	M. Lukšič (University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškerčeva c. 5, SI-1000 Ljubljana, Slovenia),
	B. Millán-Malo (Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, A.P. 1-1010, 76000 Querétaro, México),
	B. Hribar-Lee (University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškerčeva c. 5, SI-1000 Ljubljana, Slovenia),
	V. Vlachy (University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškerčeva c. 5, SI-1000 Ljubljana, Slovenia)

Accuracy of the mean activity coefficient expression (Hansen-Vieillefosse-Belloni equation), valid within the hypernetted chain (HNC) approximation, was tested in a wide concentration range against new Monte Carlo (MC) data for +1:-1 and +2:-2 primitive model electrolytes. The expression has an advantage that the excess chemical potential can be obtained directly, without invoking the time consuming Gibbs-Duhem calculation. We found the HNC results for the mean activity coefficient to be in good agreement with the machine calculations performed for the same model. In addition, the thermodynamic consistency of the HNC approximation was tested. The mean activity coefficients, calculated via the Gibbs-Duhem equation, seem to follow the MC data slightly better than the Hansen-Vieillefosse-Belloni expression. For completeness of the calculation, the HNC excess internal energies and osmotic coefficients are also presented. These results are compared with the calculations based on other theories commonly used to describe electrolyte solutions, such as the mean spherical approximation, Pitzer's extension of the Debye-Hückel theory, and the Debye-Hückel limiting law.

Key words: primitive model electrolyte, mean activity coefficient, hypernetted-chain approximation, mean spherical approximation, Monte Carlo simulation, Pitzer's approach, Debye-Hückel theory
PACS: 02.30.Rz, 05.10.Ln, 05.20.Jj, 05.70.Ce, 82.45.Gj, 82.60.Lf

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