Direct, atomic orbital, static exchange calculations of photoabsorption spectra of large molecules and clusters

We outline a method for static exchange calculations of the photoabsorption spectra of large molecules and clusters, with particular attention to near-edge X-ray absorption fine structures. The static exchange matrices are determined directly from one- and two-electron integrals computed in the atomic orbital basis. Expensive storing and retrieving of integrals is thereby avoided and applications on large species possible. As a demonstration we calculate the discrete and continuum near-edge X-ray absorption spectra for molecules in the n-alkylnitrile sequence CH₃(CH₂)_nCN.