What is the definition of electron affinity in solids?

[Borek]

I was always under impression that electron affinity is defined (and listed in tables), as energy change when isolated atom in gaseous phase gains an electron.

However, I was lately told that the same term is used for solids in "standard semiconductors references", like in Sze's Physics of semiconductor devices. Obviously that would mean quite different thing and can be confusing at first.

Unfortunately I don't have access to any books to check if that's the case. Anyone can confirm?

 

[cgk]

The "electron affinity" of a neutral species X is defined as the energy of X anion minus X neutral. It works for atoms, molecules, and solids (large molecules in some sense...).

Molecules have the special characteristic of having distinct vertical and adiabatic electron affinities (for the adiabatic EA, the molecular geometry of the anion is relaxed, for the vertical the geometry of the neutral is taken). Solids have the special characteristic that ionization potential and electron affinity are closely related to electronic excitation energies, because the holes and particles of excitations can spatially separate and act like screened local cations/anions without influencing each other.