Dirac function linear Hamiltonian

The effect of the Breit interaction on the wave function can be conveniently studied by comparing radial moments (r) of shells calculated with Dirac-Coulomb and Dirac-Coulomb-Breit Hamiltonians. The effect is not very large as can be seen for Li- and Be-like ions in Figure 9.4. From the plot we note that the effect of the Breit interaction on the radial functions is small, but increases linearly with the nuclear charge number Z. Moreover, the four different models to describe the positive nuclear charge distribution (point-like, exponential, Gaussian shaped and Fermi) can hardly be distinguished. 

The response kernel for the Hartree and the exchange energy functionals is /j, +fx = (u = (l/r12)(l — Pn), in agreement with Dirac [13] and with the second-quantized Hamiltonian. The response kernel fc is a linear operator such that... 

---