Core Excitation energies, X-ray absorption

The key MODIFYEXCITATION can be used to reduce the computational costs of core excitation energies, by allowing only selected occupied orbitals and or selected virtual orbitals in the TDDFT calculations. This can also be used in case of spin-orbit coupling. In this scheme the complete one-electron excited state configuration space is reduced to the subspace where only the core electrons are excited, see Stener et al. [169]. In the actual implementation this is done by artificially changing the orbital energies of the uninteresting occupied orbitals to a large negative value (default -1d6 hartree), and by by artificially changing the orbital energies of the uninteresting virtual orbitals to a large positive value (default 1d6).

MODIFYEXCITATION
   UseOccRange elowocc ehighocc
   UseVirtRange elowvirt ehighvirt
   UseOccupied
      irrep orbitalnumbers
      irrep orbitalnumbers
      ...
   SubEnd
   UseVirtuaL
      irrep orbitalnumbers
      irrep orbitalnumbers
      ...
   SubEnd
   SetOccEnergy esetocc
   SetLargeEnergy epsbig
   UseScaledZORA
end

UseOccRange elowocc ehighocc

Use only occupied orbitals which have orbital energies between elowocc and ehighocc.

UseVirtRange elowvirt ehighvirt

Use only virtual orbitals which have orbital energies between elowvirt and ehighvirt.

UseOccupied

Use only the occupied orbitals for which are specified.

UseVirtual

Use only the virtual orbitals for which are specified.

irrep

The name of one of the irreducible representations (not a subspecies) of the point group of the system. See the Appendix for the irrep names as they are used in ADF.

orbitalnumbers

A series of one or more numbers: include all numbers of the orbitals that are to be used. In an unrestricted calculation the same numbers are used for the spin-α orbitals and the spin-β orbitals.

SetOccEnergy esetocc

All occupied orbitals that have to be used will change their orbital energy to esetocc. In practice only useful if one has selected one occupied orbital energy, and one want to change this to another value. Default: the orbital energies of the occupied orbitals that are used are not changed.

SetLargeEnergy epsbig

The orbital energies of the uninteresting occupied orbitals are changed to -epsbig hartree, and the orbital energies of the uninteresting virtual orbitals are changed to epsbig hartree (Default: epsbig = -1d6 hartree).

UseScaledZORA

Use everywhere the scaled ZORA orbital energies instead of the ZORA orbital energies in the TDDFT equations. This can improve deep core excitation energies. Only valid if ZORA is used. Default: use the unscaled ZORA orbital energies.