Es=mec2{Co−f(rph)}
where, f(r)=ln(r)−C.r and
Co=f(rs).
rs is the normal radius of the electron around the proton that the electron return to after the passing of an incident photon; rph is the minimum radius of the orbit as the electron is pushed towards the proton when an incident photon passes through.
When rs=rph, ie that the electron is not pushed further towards the proton.
Es=0
EP=12Eb which is a constant.
We move rph towards rs by decreasing the incident photon frequency.
EP=constant
suggests that there is a minimum frequency of the incident photon that must provide for EP=12Eb, below which there is no emitted photon. EP does not decrease continuously to zero with decreasing incident photon frequency.
EP=12Eb=Φw
From this we deduce that the work function, Φw is half the bond energy.