Wikipedia - Lavoro di estrazione (it) electron work function, $$\mathit{\Phi}$$

https://doi.org/10.1351/goldbook.E02015
The minimum work needed to extract electrons from the @F02341@ of a metal M across a surface carrying no net charge. It is equal to the sum of the potential energy and the kinetic @F02340@ taken with the reverse sign: $\mathit{\Phi} ^{M} = -(V_{\text{e}}+ɛ_{\text{e}}^{F})$ where $$V_{\text{e}}$$ is the potential energy for electrons in metals and $$\varepsilon_{\text{e}}^{\text{F}}$$ is the @K03402@ of electrons at the @F02341@.
Source:
PAC, 1986, 58, 437. (Interphases in systems of conducting phases (Recommendations 1985)) on page 441 [Terms] [Paper]