Ground states of H, He,…, Ne, and their singly positive ions in strong magnetic fields: The high-field regime

The electronic structure of the ground state and some excited states of neutral atoms with the nuclear charge numbers $1<~Z<~10$ and their singly positive ions are investigated by means of our two-dimensional mesh Hartree-Fock method for strong magnetic fields $0.5<~\gamma <~10000.$ For $\gamma =10\mathrm{}000$ the ground-state configurations of all the atoms and ions considered are given by fully spin-polarized configurations of single-electron orbitals with magnetic quantum numbers ranging from $m=0\mathrm{}$ to $m=-N+1,$ where N is the number of the electrons. Focusing on the fully spin-polarized situation, we provide critical values of the magnetic-field strength for which crossovers with respect to the spatial symmetries of the ground state take place. It is found that the neutral atoms and singly charged positive ions with $2<~Z<~5$ have one fully spin-polarized ground-state configuration, whereas for $6<~Z<~10$ one intermediate fully spin-polarized configuration with an orbital of ${2p}_0$ type occurs.