  The Breit interaction is implemented in the no-pair variational Dirac-Coulomb
(DC) framework using an explicitly correlated Gaussian basis reported in the
previous paper [Paper I: P. Jeszenszki, D. Ferenc, and E. M\'atyus (2022)].
Both a perturbative and a fully variational inclusion of the Breit term is
considered. The no-pair DC plus perturbative Breit as well as the no-pair
Dirac-Coulomb-Breit energies are compared with perturbation theory results
including the Breit-Pauli Hamiltonian and leading-order non-radiative quantum
electrodynamics corrections for low $Z$ values. Possible reasons for the
observed deviations are discussed.
