The amount of energy that metal must absorb before it can release a photoelectron from the metal.

The energy required for an electron to escape a solid surface. See Helmholtz function. In ion engines, the work function of the ionizer must be greater than the ionization potential of the neutral atoms in the propellant gas.

(): The amount of energy needed to release an electron from the attraction of positive ions in a metal. It is different for different metals. [H76

The minimum energy required to remove an electron from the Fermi level of a material into field-free space. Work function is normally expressed in electron volts.

The work function is the minimum energy (usually measured in electron volts) needed to remove an electron from a solid to a point immediately outside the solid surface. Here "immediately" means that the final electron position is far from the surface on the atomic scale but still close to the solid on the macroscopic scale. Work function is an important property of metal.