In order to access these options you should select the EXPERT OPTIONS sheet (close to the upper left corner of the main program window).
There are two options to modify the target specification:
USE OSCILLATOR STRENGTHS option
Without selecting this option, the whole spectrum of dipole-oscillator strengths for low electronic energy transfers is replaced by a single (representative) oscillator for each target subshell. The corresponding energy transfer summed over all shells is given by the mean target-ionization potential I_Bethe, similar as in the simple Bethe formula. A proportionality between oscillator energy and binding energy is assumed for the distribution of the oscillator energies over all electronic shells.
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This option is provided for advanced users only.
When selecting this option, a popup-window will ask for the directory and for the name of an ASCII file containing numerical OSCILLATOR STRENGTHS for the target K-shell. The name of this file must be “Osc1.dat”. The names Osc2.dat, Osc3.dat, and so forth are reserved for the other shells (2s, 2p, …). It is recommended to use a separate subdirectory for each target system and to store all the corresponding “Osc*.dat” files in these directories.
Each of the files must contain a list of oscillator strengths (a single line for each transition) in an ascending order of the energy. For each transition, the final-state energy has to be given first (in atomic units, 1 a.u.=27.2 eV) and the corresponding oscillator strength as a second parameter (also in atomic units). For continuum states the oscillator strengths have to be integrated over the energy bin, corresponding to the specific continuum energies. Internally, CasP will just sum over all oscillator strengths (no advanced integration or extrapolation is performed here).
Note that one sample file “Osc1.dat” is included within this package. This file contains numerical oscillator strengths for the hydrogen atom and should be stored in the subdirectory “OscH”. Another set of sample files “Osc1.dat” to “Osc3.dat” for carbon, calculated from Hartree-Fock-Slater wave functions, should be stored in the subdirectory “OscC”. For intermediate and especially for large impact parameters, the use of numerical oscillator strengths improves the results. For many atoms, numerical values or fits to dipole-oscillator strengths may be found in the literature.
GAS TARGET option
Without selecting this check box, the target is assumed to be an amorphous solid or a liquid of similar target density (otherwise a low density gas target). This option will only influence the mean projectile charge state (for pure elements as well as also for the compound targets).