**Scalar Relativistic calculations: Douglas-Kroll-Hess** The Douglas-Kroll transformation gives a two-component formalism with an eﬀective Hamiltonian, containing spin-dependent and spin-independent terms.

Hess worked out a practical formulation in terms of matrix algebra.

Averaging over spin gives a spin-independent scalar Hamiltonian.

Technically, this just amount to changing the interactions by changing the one- and maybe two-electron integrals.

This can be done for eﬀective core potentials by parametrizing to represent the scalar relativistic eﬀects. It can also be done by including in the integral generator the procedure for changing the interactions

__See also:__ Scalar Relativity

http://www.oraxcel.com/cgi-bin/yabb2/YaBB.pl?num=1325284119/0#0 N. Douglas and N. M. Kroll. Ann.Phys., 82:89, 1974

B.A. Hess. Phys.Rev. A, 33:3742, 1986

__Source:__ http://www.molcas.org/wsh/lectures.bojnice/Lec06.pdf