The focus of Dr. Brown’s career has been understanding the physics that lies behind the empirical bond model used to describe the structures of organic molecules. He has developed the bond valence model which provides a similar description for inorganic compounds, and he has shown that the bond valence, i.e., the amount of charge an atom uses to form a bond, is the same as the electrostatic flux that links the negative bonding charge to its positive atomic core. The flux is proportional to the number of Faraday lines of field linking these two charges, and since the flux does not depend on where the charge is located, the theory independent of the charge distribution described by quantum mechanics. This allows classical electrostatic theory to be used to derived a set of simple theorems for modelling chemical structures, answering questions such as: which atoms will bond to each other, how many bonds does each atom form, and what is the length of the resulting bonds? The flux theory describes all localize bonds, both covalent and ionic. It extends the scope of the VSEPR model and explains why hydrogen bonds are asymmetric. It can be used to predict and analyse complex inorganic structures, for example by quantifying the spatial stresses responsible for the unusual electrical properties of perovskites, or tracing the paths of the mobile ions in an ionic conductor. Unlike the Lewis and orbital models, the flux theory gives a correct physical description of the chemical bond, leading, for example, to a simple prediction of solubility, and modelling the structures of aqueous solutions and surfaces.
Developing the bond valence model started with deriving empirical rules from the large numbers of reported inorganic crystal structures, work that required crystallographic databases and a common crystallographic file structure. To meet these needs Dr. Brown pioneered both the Inorganic Crystal Structure Database and the CIF crystallographic file structure. He was an editor of Acta Crystallographica and served on several commissions of the International Union of Crystallography and committees of the American Crystallographic Association.