With a workable expression for the electron energy density in hand, we can use it to partition materials into atomic fragments, or basins 𝛺 7 . 1 Atomic basins 𝛺 7 are here defined from threedimensional seams at which ∇𝛸(𝒓) • 𝒏(𝒓) = 0 , where ∇𝛸(𝒓) is the gradient of the electron energy density and where 𝒏(𝒓) is the unit vector normal to the surface at 𝒓. Our procedure technically mirrors that of QTAIM, where the condition for defining a basin is instead ∇𝜌(𝒓) • 𝒏(𝒓) = 0. As we have illustrated in our previous work focused on molecules, and as we shall see, the resulting atomic basins derived from 𝛸(𝒓) and 𝜌(𝒓) are notably different. We will refer to electron energy basins, 𝛺 7 , to distinguish our partitioning approach from QTAIM.