Harmonic approximation and linear response (Green's function) of an arbitrary system

Michael G Cottam, Zahra Haghshenasfard

Yoshio Kuramoto

Taichi Kosugi, Yu‐ichiro Matsushita

Mizuhiko Saeki

Viorica Florescu, Tudor A. Marian

We investigate the linear response of a nonrelativistic hydrogenlike atom to a harmonic uniform electric field, which is switched on adiabatically. For the electron initially in an arbitrary bound \ensuremath{\Vert}nlm〉 state, the first-order correction to the wave function has been written in terms of a vector function ${\mathrm{w}}_{\mathrm{nlm}}$. We report an exact closed-form expression of the vector ${\mathrm{w}}_{\mathrm{nlm}}$ that we have derived using the Coulomb Green's function. Our general analytic results prove to be useful in a systematic study of two-photon processes involving the hydrogen atom.

Dennis Dunn

We consider a one-dimensional fermion model which is similar to the Luttinger model and which also includes an electron-phonon interaction. We show that in this model the electron, phonon, and plasmon Green functions can all be determined exactly.We examine the dielectric properties of the system and also the more general response of the system to arbitrary external fields and we show that the response is strictly linear in these fields.