Multi-electron systems in strong magnetic fields I: The 2D Landau-Hartree-Fock-Roothaan method

We present a 2-dimensional Hartree-Fock-Roothaan code to calculate wave functions and energies of light to heavy atoms in strong external magnetic fields, as they occur in the vicinity of neutron stars. The code enhances the previously presented HFFER II method, resulting in a very high precision for the energies with typical deviations less than 1% compared to the extremely precise fixed-phase diffusion quantum Monte Carlo method presented in the accompanying paper []. Despite this high precision the code is highly optimised regarding speed and reliability, which allows calculating large amounts of states in short time, even with small-scale computing clusters.