Density-functional-theory calculations of matter in strong magnetic fields. I. Atoms and molecules

We present calculations of the electronic structure of various atoms and molecules in strong magnetic fields ranging from B=1012 G to 2x1015 G, appropriate for radio pulsars and magnetars. For these field strengths, the magnetic forces on the electrons dominate over the Coulomb forces, and to a good approximation the electrons are confined to the ground Landau level. Our calculations are based on the density functional theory, and use a local magnetic exchange-correlation function which is tested to be reliable in the strong field regime. Numerical results of the ground-state energies are given for HN (up to N=10), HeN (up to N=8), CN (up to N=5), and FeN (up to N=3), as well as for various ionized atoms. Fitting formulae for the B dependence of the energies are also given. In general, as N increases, the binding energy per atom in a molecule, vertical bar EN|/N, increases and approaches a constant value. For all the field strengths considered in this paper, hydrogen, helium, and carbon molecules are found to be bound relative to individual atoms (although for B less than a few x1012 G, carbon molecules are very weakly bound relative to individual atoms). Iron molecules are not bound at B < or approx. 1013 G, but become energetically more favorable than individual atoms at larger field strengths