<!-- Thanks for providing feedback! Please provide the information below. --> ## Sommerfeld model ## If we impose periodic boundary conditions, ψ(x,y,z)=ψ(x+l,y+L,z+L), it follows that the allowed wavenumbers are given by ## If we impose periodic boundary conditions, ψ(x,y,z)=ψ(x+L,y+L,z+L), it follows that the allowed wavenumbers are given by