An atomic layer deposition apparatus, including: a chamber with an internal volume; a fixture assembly to hold a substrate within the internal volume of the chamber; a plurality of gas injection ports to facilitate the introduction of gas; at least one precursor gas arrangement to introduce precursor gas into the internal volume; and at least one inactive gas dispersion arrangement to introduce inactive gas into the internal volume. The inactive gas dispersion arrangement is in the form of a primary dispersion member configured to concentrically focus the precursor gas towards a surface of the substrate. A modeling system for an atomic layer deposition apparatus is also disclosed.