  Broadly speaking, the calculation of core spectra such as electron energy
loss spectra (EELS) at the level of density functional theory (DFT) usually
relies one of two approaches: conceptually more complex but computationally
efficient projector augmented wave based approaches, or more straightforward
but computationally more intensive all election (AE) based approaches. In this
work we present an alternative method, which aims to find a middle ground
between the two. Specifically, we have implemented an approach in the
multi-wavelet MADNESS molecular DFT code which permits a combination of atoms
treated at the AE and pseudopotential (PSP) level. Atoms for which one wishes
to calculate the core edges are thus treated at an AE level, while the
remainder can be treated at the PSP level. This is made possible thanks to the
multiresolution approach of MADNESS, which permits accurate and efficient
calculations at both the AE and PSP level. Through examples of a small molecule
and a carbon nanotube we demonstrate the potential applications of our
approach.
