OCEAN is a versatile package for calculating both optical/UV and core-edge spectroscopy. It is a first-principles code based on both ground-state density-functional theory (DFT) and the Bethe-Salpeter equation (BSE).
On the right is shown the resonant inelastic x-ray scattering spectra of lithium peroxide as measured in experiment and calculated using OCEAN. The circled feature was identified as a fingerprint of oxygen oxidation in this system.
OCEAN is capable of calculating a variety of spectra, including:
Postdoc positions at NIST are available through the National Academies. Specific listings are here and here, and more general information can be found here.