(color online) (a) and (c): Three-dimensional views of λ k i in the reciprocal unit cell. Panels (b) and (d): charge densities of electrons that couple most strongly with phonons. Panels (a) and (b) correspond to 0.4 e/cell doping without BTS. Panels (c) and (d) correspond to 0.2 e/cell doping with 8% BTS.