Rotational invariance of <scp>INDO</scp> theories including <i>d</i>‐orbitals into the basis set

Abstract

Abstract It is proved that in general the INDO approximation to the full Roothaan theory does not lead to expressions which are invariant under a rotation of local atomic axes. However, when only s ‐ and p ‐functions are used in the atomic basis set, the equations obtained are invariant due to the special properties of the p ‐functions. When d ‐orbitals are included into the basis set, rotational invariance is lost but can be restored if a supplementary approximation is introduced.