The Mg K-edge and Zn K- and L3-edge X-ray absorption near edge spectra of Mg and Zn porphyrins in the ground state and low-lying optically excited states are calculated. Also computed are X-ray absorption near edge spectra of Fe(II) spin crossover compound in its ground and low-lying optically excited states, motivated by a recent experiment (J. Phys. Chem. A 2006, 110, 38). The calculated absorption spectra of optically excited states can be used to simulate ultrafast optical pump/X-ray probe experiments.

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The x-ray absorption near-edge spectra (XANES) and fluorescence spectra of molecules in the ground state and optically excited states are computed using time-dependent density functional theory and time-dependent Hartree-Fock theory. The calculated XANES spectra of optically excited methanol, benzonitrile, hydrogen sulphide, and titanium tetrachloride and the fluorescence spectra of optically excited methanol can be used to simulate ultrafast optical pump/x-ray probe experiments.

We carry out detailed studies of charged (D+) and neutral (D0) impurity states of helium-like donors in spherical semiconductor quantum dots using both the density functional-effective mass and tight-binding formalisms. We find the two sets of results to be consistent with each other down to very small size quantum dots. We vary the shape of the confining potential, taking it to be square, harmonic and triangular. Independent of the confining potential, we observe a shallow to deep transition of the donor level as the dot size is reduced. However, on further reduction of the size the donor level tends to become shallow again. This suggests that carrier ‘freeze out’ is a distinct possibility for both D+ and D0. Further, optical gaps also show similar behaviour with the size of the dot.