Combining rules

The combining rules (also known as mixing rules) for binary mixtures are variously given by

Berthelot rule

$\epsilon _{ij}={\sqrt {\epsilon _{ii}\epsilon _{jj}}}$

Lorentz rule

$\sigma _{ij}={\frac {\sigma _{ii}+\sigma _{jj}}{2}}$

See also Lennard-Jones model

Admur and Mason

For the second virial coefficient of a mixture (Ref. 1)

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle B_{ij} = \frac{\left(B_{ii}^{1/3}+B_{jj}^{1/3}\right)^3}{8}}

References

1. I. Amdur and E. A. Mason "Properties of Gases at Very High Temperatures", Physics of Fluids 1 pp. 370-383 (1958)