Ground state of the carbon atom in strong magnetic fields

The ground and a few excited states of the carbon atom in external uniform magnetic fields are calculated by means of our two-dimensional mesh Hartree-Fock method for field strengths ranging from zero up to 2.35×10⁹ T. With increasing field strength the ground state undergoes six transitions involving seven different electronic configurations which belong to three groups with different spin projections Sz=-1,-2,-3. For weak fields the ground-state configuration arises from the field-free 1s²2s²2p₀2p_-1, Sz=-1 configuration. With increasing field strength the ground state involves the four Sz=-2 configurations 1s²2s2p₀2p_-12p₊₁, 1s²2s2p₀2p_-13d_-2, 1s²2p₀2p_-13d_-24f_-3, and 1s²2p_-13d_-24f_-35g_-4, followed by the two fully spin-polarized Sz=-3 configurations 1s2p₀2p_-13d_-24f_-35g_-4 and 1s2p_-13d_-24f_-35g_-46h_-5. The last configuration forms the ground state of the carbon atom in the high-field regime γ>18.664. The above series of ground-state configurations is extracted from the results of numerical calculations for more than 20 electronic configurations selected due to some general energetic arguments.