When Bosanquet Approximation (Kn ≅ 1) is chosen from the pull-down menu in the DiffuDict section, clicking the Options’ Edit… button opens the Bosanquet Approximation dialog box.

The Mean Thermal Velocity is the average speed of the thermal motion of particles, which make up a gas, liquid, etc. It can be calculated by

where is the Boltzmann constant, the temperature and the molecular mass.

The Mean Free Path Length is the average distance traveled by a moving particle between successive collisions with other molecules. The default Mean Thermal Velocity value of 464 m/s and Mean Free Path Length value of 68 nm roughly correspond to air/nitrogen at ambient temperature (20° C, 293° K) and pressure (1013 bar, 1 atm).

Bulk (Laplace) Diffusion and Knudsen Diffusion must be previously computed and the path to the corresponding result files must be loaded using the Browse buttons. The loaded result files must correspond to calculations of Bulk (Laplace) Diffusion and Knudsen Diffusion, respectively. Otherwise, a warning appears when clicking OK in the Bosanquet Approximation dialog box. The loaded result files must also correspond to the current structure; otherwise, an error message is displayed after clicking Run.