Setting various two-component Hamiltonians

From Diracwiki

There are several two-component Hamiltonians in DIRAC arising from the decoupling transformation of the one-electron DIRAC Hamiltonian. Likewise spin-orbit interaction terms can be left out and calculations can be preformed in the spin-free mode (ie in boson symmetry).

Besides having spin-orbit effects from the decoupling transformation, there is the external AMFI spin-orbit operator which can contribute either with the one-electron spin-orbit operator (accurate to the first order in V, very poor) or with the more valuable mean-field contribution, u_so(1) (also in the first order), which is reasonable approximation of the 'Gaunt' term from the four-component level.

The best two-component Hamiltonian is BSS+MFSSO, or IOTC+MFSSO, where one-electron scalar and spin-orbit effects are up to infinite order, and AMFI MFSSO contribution (mean-field spin-same orbit) provides 'screening' of one-electron spin-orbit terms.