Exchange and correlation energies of ground states of atoms and molecules in strong magnetic fields

Using a Hartree-Fock mesh method and a configuration-interaction approach b ased on a generalized Gaussian basis set, we investigate the behavior of th e exchange and correlation energies of small atoms and molecules, namely, t he helium and lithium atoms as well as the hydrogen molecule, in the presen ce of a magnetic field covering the regime B = 0-100 a.u. In general, the i mportance of the exchange energy to the binding properties of atoms or mole cules increases strongly with increasing field strength. This is due to the spin-flip transitions, and in particular due to thr contributions of the r ightly bound hydrogenic states which are involved in the corresponding grou nd states of different symmetries. In contrast to the exchange energy the c orrelation energy becomes less relevant with increasing field strength. Thi s holds for the individual configurations constituting the ground state and for the crossovers of the global ground state. [S1050-2947(99)06105-7].