title: Adiabatic connection forms in density functional theory: H2 and the He isoelectronic series.
abstract: Full configuration interaction (FCI) data are used to quantify the accuracy of approximate adiabatic connection (AC) forms in describing two challenging problems in density functional theory--the singlet ground state potential energy curve of H(2) in a restricted formalism and the energies of the helium isoelectronic series, H(-) to Ne(8+). For H(2), an exponential-based form yields a potential energy curve that is virtually indistinguishable from the FCI curve, eliminating the unphysical barrier to dissociation observed previously with a [1,1]-Pade-based form and with the random phase approximation. For the helium isoelectronic series, the Pade-based form gives the best overall description, followed by the exponential form, with errors that are orders of magnitude smaller than those from a standard hybrid functional. Particular attention is paid to the limiting behavior of the AC forms with increasing bond distance in H(2) and increasing atomic number in the isoelectronic series; several forms describe both limits correctly. The study illustrates the very high quality results that can be obtained using exchange-correlation functionals based on simple AC forms, when near-exact data are used to determine the parameters in the forms.
authors: Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, United Kingdom.
authors: Michael J G
authors: MJ
authors: Peach
authors: Adam M
authors: AM
authors: Miller
authors: Andrew M
authors: AM
authors: Teale
authors: David J
authors: DJ
authors: Tozer