Calculations of binary diffusion coefficients and thermal diffusion factors of gaseous neon-argon and helium-krypton mixtures from state-of-the-art ab initio pair potentials

E. Bich1, R. Hellmann1, B. Jäger1 and E. Vogel1

1Institute of Chemistry, University of Rostock, Rostock, Germany

Keywords: ab initio calculations
property: binary diffusion coefficients, thermal diffusion factors
material: noble gas mixtures

The binary mixtures neon-argon and helium-krypton represent model systems which can be used for the calibration of measuring instruments for binary and thermal diffusion. For that purpose highly accurate values of the transport properties can be calculated from the kinetic theory of gases. Prerequisite for that are accurate potential energy curves for all pairwise interactions between the atoms in the mixture.

Interaction energies for all pair potentials involved have been computed for a large number of interatomic distances at the CCSD(T) level of theory with the best available basis sets. Counterpoise correction, frozen-core approximation and extrapolation of the correlation energy to the complete basis set limit have been applied. Furthermore, corrections for core-core and core-valence correlation, for relativistic effects and for the impact of higher coupled-cluster terms (CCSDT,CCSDT(Q)) have been included. Analytical potential functions of the HFD-ID type have been fitted to the resulting interaction energies of each pair of atoms.

The binary diffusion coefficients and the thermal diffusion factors of the considered mixtures have been determined and compared with experimental data. All results show close agreement with the best experimental data in restricted temperature ranges. The theoretical values are generally more reliable than the experiments at all temperatures relevant for practical purposes.

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