A partial differential equation which describes an interatomic surface

In this work we present a first‐order partial differential equation which defines the topology of single ‘atomic entities’ in multiatomic systems. Such an equation, obtained by R. F. W. Bader, is here analysed and discussed from a general mathematical point of view; a method is then proposed for defining the initial or boundary condition. With this contribution we would like to promote and stimulate a more detailed analysis which goes beyond practical purposes and basic mathematical analysis in order to have a deeper understanding of the theory behind the equation and its consequences for practical applications.