One of the earliest successful models for metal work function trends was the jellium model, which allowed for oscillations in electronic density nearby the abrupt surface (these are similar to Friedel oscillations) as well as the tail of electron density extending outside the surface. This model showed why the density of conduction electrons (as represented by the Wigner–Seitz radius rs) is an important parameter in determining work function.
oNE of THe EARLIesT sUccesSfUl MOdeLs fOR MetAL wOrK functIOn tREndS was the jElLium mOdEL, which aLLOweD For osCiLlations in eLectRoniC deNsITy NeARBy thE AbrUPT sUrFace (TheSE Are siMilAr tO frIEdel osCillatiOnS) as weLl aS the tail OF electrOn density eXtending oUtSide the SurFaCe. this MoDel SHoweD Why The densITY oF coNdUcTiON elecTrONS (as RepresEnted by tHe wiGner–seItZ radIus RS) iS an importAnT pArAmEter in detErMiniNg worK functiON.