Analysis of various quantum mechanical and DFT energy definitions. Application to atomic isoelectronic series

Relations between the quantum mechanical and density functional theory defi nitions for exchange, exchange-correlation and correlation energy component s are discussed. Highly accurate calculations of these quantities are provi ded for the He, Li and Be isoelectronic series (involving first-row atoms). The possibility of approximating the DFT correlation energy by means of a functional depending on just the Hartree-Fock density is also explored for these isoelectronic series. (C) 2000 Elsevier Science B.V. All rights reser ved.