title: Beyond the random-phase approximation for the electron correlation energy: the importance of single excitations.
abstract: The random-phase approximation (RPA) for the electron correlation energy, combined with the exact-exchange (EX) energy, represents the state-of-the-art exchange-correlation functional within density-functional theory. However, the standard RPA practice--evaluating both the EX and the RPA correlation energies using Kohn-Sham (KS) orbitals from local or semilocal exchange-correlation functionals--leads to a systematic underbinding of molecules and solids. Here we demonstrate that this behavior can be corrected by adding a "single excitation" contribution, so far not included in the standard RPA scheme. A similar improvement can also be achieved by replacing the non-self-consistent EX total energy by the corresponding self-consistent Hartree-Fock total energy, while retaining the RPA correlation energy evaluated using KS orbitals. Both schemes achieve chemical accuracy for a standard benchmark set of noncovalent intermolecular interactions.
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany.
authors.forename: Xinguo
authors.initials: X
authors.lastname: Ren
authors.forename: Alexandre
authors.initials: A
authors.lastname: Tkatchenko
authors.forename: Patrick
authors.initials: P
authors.lastname: Rinke
authors.forename: Matthias
authors.initials: M
authors.lastname: Scheffler