Perturbation theory Z expansion for many-electron autoionising states of atomic systems

A theory for calculating energies and wavelengths using the Z-expansion technique is presented: it is suitable for degenerate autoionisation states of many-electron ions (configurations 1s2ssup(n1)2psup(n2)). The Hartree-Fock energy, correlation energy and relativistic corrections have been taken into account. To calculate the relativistic part the first non-zero term of the expansion in powers of Zα was considered, which, in fact, is described by the Breit Hamiltonian. Four-electron systems are considered as an example. (author)