Setting up a core hole calculation

Calculations with core holes are designed to describe the electronic structure of a system containing highly exited ions with a hole in a core shell. Such calculations can be relevant to the description of such excitations and relaxations of these excited states.

Core holes can be used in any CASTEP calculation, however they are most relevant to the generation of core level spectroscopy results. It is not recommended to carry out geometry optimizations in the presence of core holes.

CASTEP calculations using core holes are only available for atoms using on-the-fly generated pseudopotentials (OTFG).

To set up a core hole calculation

Either import a structure from a pre-existing file or construct a new structure using the sketching and crystal building tools in the Materials Visualizer.
Extend the crystal lattice using the Supercell or Redefine Lattice dialog and convert to the primitive representation.
Convert the symmetry of the crystal to P1, to prevent core holes being placed on symmetrically equivalent atoms.
Select Modify | Electronic Configuration from the menu bar to display the Core Hole tab of the Electronic Configuration dialog.
Set up the core hole(s) in the structure as desired (see Changing Core Hole values for further guidance). Close the Electronic Configuration dialog.
Open the Find Symmetry dialog and select the Options tab. Check the CoreShellWithHole checkbox in the list of properties. On the Find tab click the Find Symmetry button then the Impose Symmetry button.
Choose Modules | CASTEP | Calculation from the menu bar to open the CASTEP Calculation dialog.
On the Electronic tab check the Use Core Hole checkbox.
Select On the fly from the Pseudopotentials dropdown list.
Click the Run button.

To prevent interactions between periodic images of core hole sites sufficiently large supercells might be necessary.

CASTEP calculations with core holes assume by default that an electron is removed from the system, so it is treated as having a charge of 1 (or one more than specified in the Charge field on the Setup tab of the CASTEP Calculation dialog). In some circumstances, for example when studying impurities, it might be more appropriate to consider the system as charge neutral. In order to achieve this you should specify the Charge of -1 on the Setup tab, in this way the CASTEP input file will have a zero charge. It is also possible to edit the seedname.param file to specify a fractional charge. The strength of the core hole can be adjusted by editing the seedname.cell file and modifying the pseudopotential definition string (for example, change {1s1} to {1s0.5} to use a core hole with the charge of 0.5).

Setting up a core hole calculation

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