\textit{Ab initio} calculations of the electron momentum distribution function for ordered and disordered warm dense matter (WDM)*

We report new calculations of the electron momentum distribution $n(p)$ for ordered and disordered materials of interest for warm dense matter research. The central role of the electron-ion interaction and the need to orthogonalize the valence-electron and core-electron wave functions has often been ignored in the interpretation of x-ray Thomson scattering studies of WDM.\footnote{Mattern, B.~A. et al. arXiv:\textbf{1308.2990} (2013)} This has led to substantial uncertainty in the inferred temperatures and ionization states in laser-shock generated dense plasmas. Real space Green's function calculations as a function of density and disorder are used to evaluate the possibility of a broadly applicable universal rescaling of the free-electron $n(p)$ by an effective volume and effective temperature to approximate the effects of valence-core orthogonalization.