Introduction - Why calculate the excess amount adsorbed?

The output of a GCMC simulation is the absolute amount adsorbed, that is, the total number of adsorbate molecules present in the pore, whereas experimentally the excess amount adsorbed is measured. The excess number of molecules, n^ex, is related to the absolute number of molecules, n^abs, by

where V^g is the pore volume of the adsorbent and rho^g is the molar density of the bulk gas phase calculated with the Peng-Robinson equation of state. We normally calculate the pore volume with the second virial coefficient as described by AL Myers and PA Monson, Langmuir 2002, 18, 10261.

Here, curly V is the fluid-adsorbent interaction of a single helium atom m is the mass of the adsorbent, and T is the temperature.

The program described here, uses equation (1) to calculate the excess amount adsorbed from the absolute amount adsorbed read from a music post file. This tutorial does not contain a description of how to calculate the pore volume. You have to supply that value in the subroutine adsorbent_properties_UFF.f90 , but it is up to you how to determine it.