Quadratically convergent multiconfiguration Dirac-Fock and multireference relativistic configuration-interaction calculations for many-electron systems

A quadratically convergent Newton-Raphson algorithm for a relativistic multiconfiguration 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 multiconfiguration wave functions constructed from one-particle Dirac spinors is described. We report the results of relativistic multiconfiguration Dirac-Fock self-consistent-field calculations and relativistic multireference configuration-interaction calculations based on the multiconfiguration Dirac-Fock wave functions for the lowest ³P₀, ³P₁, and ³P₂ states of oxygenlike iron (Fe¹⁸⁺), ground $J=0$ and excited $J=1$ states of beryllium, and ground-state berylliumlike neon (Ne⁶⁺), species that exhibit the near degeneracy characteristic of a manifold of strongly interacting configurations.