Introduce the complex potential V = −(U +iW) in the Schrodinger’s equation
∇2ψ + 2m2(E + U + iW)ψ = 0 ...(1)

where v is the particle velocity and the mean free path λ = 1/K. When steady state has reached the first term on the LHS of (7) vanishes. Provided W > 0, the imaginary part of the complex potential has the effect of absorbing flux from the incident channel.