Solution (source code)

= Solution

Write the full equation as $L\psi_s=-U\psi_s$. Apply the outgoing inverse of $L$ and add the incident <homogeneous solution> with unit left-incident <amplitude>. This gives
$$
\boxed{\psi_s(x)=e^{ikx}-\frac{im}{k\hbar^2}\int e^{ik|x-x'|}U(x')\psi_s(x')dx'.}
$$
For sufficiently short-range potentials this is the outgoing <Lippmann-Schwinger equation>. The minus sign follows from the definition $L=H_0-E$, rather than $E-H_0$.