  Replacement of hydrogen by deuterium in palladium hydride results in higher
superconducting temperatures and an anomalous isotope effect that has not been
yet fully explained. In this work, we try a new approach to the explanation of
the inverse isotope effect in PdH(D). Our approach introduces two new aspects.
First, we took into account the experimental evidence that at temperatures
below 50 K, the crystal structure of PdH and of PdD is zincblende. Second, we
take into account not only the influence of the electron-phonon interaction but
also the electron-electron interaction contribution to the isotope coeffiecient
due tothe replacement of deuterium in the place of hydrogen. We used the
Migdal-Eliashberg theory to perform our ab initio calculations. We found in
this picture that the electron-electron interaction is considerably reduced by
the isotope substitution and is the most important factor to explain the
inverse isotope effect. We found $\Delta T_c^{total}=2.224\:K$ and $\alpha=
-0.3134$ in excellent agreement with the values found experimentally.
