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== Physical factors that determine the work function ==
Due to the complications described in the modelling section below, it is difficult to theoretically predict the work function with accuracy. Various trends have, however, been identified. The work function tends to be smaller for metals with an open lattice,{{what|date=october 2020|reason=open not defined}} and larger for metals in which the atoms are closely packed. It is somewhat higher on dense crystal faces than open crystal faces, also depending on [[surface reconstruction]]s for the given crystal face.▼
▲Due to the complications described in the modelling section below, it is difficult to theoretically predict the work function with accuracy. Various trends have, however, been identified. The work function tends to be smaller for metals with an open lattice, and larger for metals in which the atoms are closely packed. It is somewhat higher on dense crystal faces than open crystal faces, also depending on [[surface reconstruction]]s for the given crystal face.
=== Surface dipole ===
The work function is not simply dependent on the "internal vacuum level" inside the material (i.e., its average electrostatic potential), because of the formation of an atomic-scale [[Double layer (interfacial)|electric double layer]] at the surface.<ref name="venables"/> This surface electric dipole gives a jump in the electrostatic potential between the material and the vacuum.
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=== Doping and electric field effect (semiconductors) ===
[[File:Semiconductor vacuum junction.svg|thumb|[[Band diagram]] of semiconductor-vacuum interface showing [[electron affinity]] ''E''<sub>EA</sub>, defined as the difference between near-surface vacuum energy ''E''<sub>vac</sub>, and near-surface [[conduction band]] edge ''E''<sub>C</sub>. Also shown: [[Fermi level]] ''E''<sub>F</sub>, [[valence band]] edge ''E''<sub>V</sub>, work function ''W''.]]
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=== Theoretical models of metal work functions ===
<!-- resource: http://venables.asu.edu/qmms/PROJ/metal1a.html -->
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