  Based on self-consistent field (SCF) atomic mean-field (amf) quantities, we
present two simple, yet computationally efficient and numerically accurate
matrix-algebraic approaches to correct both scalar-relativistic \textit{and}
spin-orbit two-electron picture-change effects (PCE) arising within an exact
two-component (X2C) Hamiltonian framework. Both approaches, dubbed amfX2C and
e(xtended)amfX2C, allow us to uniquely tailor PCE corrections to mean-field
models, $viz.$ Hartree-Fock or Kohn-Sham DFT, in the latter case also avoiding
the need of a point-wise calculation of exchange-correlation PCE corrections.
We assess the numerical performance of these PCE correction models on spinor
energies of group-18 (closed-shell) and group-16 (open-shell) diatomic
molecules, achieving a consistent $\approx\!10^{-5}$ Hartree accuracy compared
to reference four-component data. Additional tests include SCF calculations of
molecular properties such as absolute contact density and contact density
shifts in copernicium fluoride compounds (CnF$_{n}$, n=2,4,6), as well as
equation-of-motion coupled cluster calculations of X-ray core ionization
energies of $5d$ and $6d$-containing molecules, where we observe an excellent
agreement with reference data. To conclude, we are confident that our (e)amfX2C
PCE correction models constitute a fundamental milestone towards a universal
and reliable relativistic two-component quantum chemical approach, maintaining
the accuracy of the parent four-component one at a fraction of its
computational cost.
