17 RELATIVISTIC CORRECTIONS

There are three ways in MOLPROto take into account scalar relativistic effects:

1. Use the Douglas-Kroll relativistic one-electron integrals.
2. Compute a perturbational correction using the Cowan-Griffin operator (see section 4.13).
3. Use relativistic effective core potentials (see section 11).

For all-electron calculations, the prefered way is to use the Douglas-Kroll Hamiltonian. It is simply activated by setting

DKROLL=1

somewhere in the input before the first energy calculation.