Photoionization density approximation, local

In the frame of the DF Theory, two approaches can be considered for photoionization the conventional Kohn-Sham (KS) method and the time dependent version of the theory (TD-DFT). Since usually the Local Density Approximation (LDA) is employed, they are often referred as the LDA and the TDLDA methods respectively. 

A TIME-DEPENDENT LOCAL DENSITY APPROXIMATION OF ATOMIC PHOTOIONIZATION... 

Concurrent with these developments, the density functional formalism has emerged as an alternative to a Hartree Fock based description of the electronic structure of atoms, molecules and solids. In its most common form as a local density approximation (LDA) the question of atomic photoionization can again be addressed. Here too, one finds that the simplest approach falls to adequately charr-. acterize the experimental results in many cases. However, a recent straightforward generalization of density functional theory to time-dependent phenomena has been applied successfully to the problem of the optical response of atoms. In particular, highly accurate photoionization cross sections can be readily obtained. The purpose of the present article is to review this time-dependent local density approximation (TDLDA), illustrate its scope and limitations and compare it to the more familiar Hartree-Fock based methods. 

The shift in measured by XPS core level binding energies between a rare gas such as xenon in the gas phase and adsorbed on a surface results from a combination of chemical shift, local potential at the site of the adsorbate, and stabilization of the photoionization core hole by polarization of the substrate electron density. As discussed in reference (13), the contribution due to substrate polarization is related to the surface electronic polarizability and can be isolated from the other contributions to a good approximation by measurements of the xenon gas phase and adsorbed phase "Auger parameter", a. a is defined as the difference between the (Jkl) core level Auger electron kinetic energy, K (jkl), and the (j) core level photoelectron kinetic energy, K (J). 

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