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Core, semi-core and valence states

In many cases it is desirable to distinguish three types of electronic states, namely core, semi-core and valence states. For example titanium has core (1s, 2s, 2p), semi-core (3s, 3p) and valence (3d, 4s, 4p) states. Core states are those whose charge is entirely confined inside the corresponding atomic sphere. They are deep in energy, e.g., more than 7-10 Ry below the Fermi energy. Semi-core states lie high enough in energy (between about 1 and 7 Ry below the Fermi energy), so that their charge is no longer completely inside the sphere, but a few percent are outside the sphere. Valence states are energetically the highest (occupied) states and always have a significant amount of charge outside the spheres.

If a system has atoms with semi-core states, then the best way to treat them is with ``local orbitals``, an extension of the usual LAPW basis. In addition LOs can also be used for valence states (e.g. d states) to improve the quality of the basis set, i.e. to go beyond the simple linearization.


next up previous contents
Next: Spin-polarized calculation Up: Flow of programs Previous: Flow of programs

2000-04-11