After a long research on electric polarization, here's what I understood (please correct if there are any misunderstanding):
In an atom (neutral), electrons are permanently moving around the nucleus (protons and neutrons). Each electron has an orbit. Electron cloud has the same barycenter of the nucleus. When an electric field is applied, electron cloud is deformed and the barycenters are no longer the same (the atom is polarized and similar to a dipole).
Does it mean that the electrons are no longer moving around the nucleus or/and they stop moving? If electrons still moving, what about the new orbits, are they the same or they are deformed and/or they barycenters are shifted ? How the new electrons motion is described ?
What I initially think, that most of the electrons moves in a cloud whose the barycenter is deviated from that of the nucleus, and the other electrons are still moving around it (the nucleus).