Nusc said:
Does NaCl have a wavefunction?
Yes.
Nusc said:
The electrons in a multielectron system like an atom, molecule, or crystal are (almost?) always entangled, but not really in any way that's useful for us. A more interesting question might be if you can decompose the wavefunction into "Na electrons" and "Cl electrons:"
$$|\Psi\rangle_{NaCl} = |\psi \rangle_{Na^+}\otimes |\psi\rangle_{Cl^-}$$
That is, are the "Na electrons" entangled with the "Cl electrons." I don't know. Probably not very, given that the simple electrostatic description that
@BvU gave is a very good approximation.
Nusc said:
An F-center is a defect in a lattice. In NaCl, it would arise as a Cl
- vacancy which is filled by an electron. It would probably be easier to control the entanglement of two F-centers than anything else in the NaCl lattice, but a quick google search didn't bring anything up for me. (I'm imagining entangling the spins of the F-centers like you would the spins of NV centers in diamonds.) There may be a reason why this isn't feasible in practice.