Figure 2: Static effective e- vertex in units of the bare e-ph coupling as a function of the transferred momentum (in units of the inverse lattice spacing ) in the direction. The vertex is calculated at leading order in for a HH model with  eV, ,  eV and doping . The dotted line is in the absence of long-range Coulomb forces ( ); the solid line is in the presence of long-range Coulomb forces with  eV (adapted from [54]).