Adiabatic connection forms in density functional theory: H(2) and the He isoelectronic series

Peach, Michael J. G. and Miller, Adam M. and Teale, Andrew M. and Tozer, David J. (2008) Adiabatic connection forms in density functional theory: H(2) and the He isoelectronic series. Journal of Chemical Physics, 129 (6). ISSN 0021-9606

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. (C) 2008 American Institute of Physics.