Second-order multiconfigurational Dirac–Fock self-consistent field and multireference configuration interaction calculations on beryllium and beryllium-like Ne6+

A quadratically convergent Newton–Raphson algorithm for relativistic multiconfigurational Dirac–Fock self-consistent field calculations is developed and implemented with analytic basis sets of Gaussian spinors. A procedure to perform second-order energy optimization for a general class of multiconfigurational wavefunctions constructed from one-particle Dirac spinors is described. We report the results of relativistic multiconfigurational Dirac–Fock self-consistent field calculations on beryllium and beryllium-like neon, followed by multireference configuration interaction with single and double excitations out of the multiconfigurational Dirac–Fock wavefunctions.