Core expansion functions

This part has the form

CORE ns, np, nd, nf
  1s 7.68
  ...
  (etc.)
  ...
end

It looks very much like the basis functions: a list of Slater type function descriptions, closed by end. The header record however (core...) contains in addition four integers ns, np, nd, nf. They are the numbers respectively of s-, p-, d-, and f- frozen core shells in the atom. If you create for instance a Ruthenium atom with a frozen core up to the 4p shell, these numbers would be 4 3 1 0 : four frozen s-shells (1s,2s,3s,4s), three frozen p-shells (2p,3p,4p), one frozen d-shell (3d), and no frozen f-shells.

The core expansion sets defined in this section are used to describe the frozen core orbitals; they are not included in the valence basis set. In the list of core expansion sets all s-type functions must come first, then the p-type functions, then the d-functions, and then the f-functions (as far as applicable).