Jellium

Jellium is the theory of interacting electrons in which a uniform background of positive charge exists. In this theory at zero temperature the system properties are dependent only on the density of electrons. This allows for the simplistic calculation of the electron-electron coupling energy being a ratio between the free-electron kinetic energy and the Coulomb potential energy.

The theory works with the atoms as if they were actually blobs of jelly, hence the name. The jellium theory is used is nuclear physics. It has been used to try to explain the properties of superatoms.