Heavy atoms in the strong magnetic field of a neutron star

The ground-state energy of an atom of nuclear charge Ze and in a magnetic field B is evaluated exactly in the asymptotic regime Z{→}{∞}. We show rigorously that there are five regions as Z{→}{∞}: B{}Z4/3, B{}Z4/3, Z4/3{}B{}Z³, B{}Z³, B{}Z³. Different regions have different physics and different asymptotic therories. Regions 1,2,3,5 are described exactly by a simple density-functional theory, but only in regions 1,2,3 is it of the semiclassical Thomas-Fermi form. Region 4 cannot be described exactly by any simple density-functonal theory; surprisingly, it can be described by a simple density matrix functonal theory.