Density functional theory (DFT) using semi-local functional approximations can describe many chemical properties to high accuracy, but in some cases large and even qualitative errors emerge. Some of these errors are ascribed to an unphysical interaction of each electron with itself, which is present as a result of the approximations made in the exchange-correlation functional. The Perdew-Zunger...

The pseudorotation of tetrahydrofuran (THF) (C(4)H(8)O) has been studied using density functional theory, with respect to the valence orbital responses to the ionization potentials and to orbital electron and momentum distributions. Three conformations of THF, the global minimum structure C(s), local minimum structure C(2), and a transition state structure C(1), which are characteristic configu...

INTRODUCTION The idea of Möbius aromaticity was first proposed by Heilbronner in 1964. He postulated that a molecule could gain Möbius aromatic stabilization if the nuclear framework were twisted so the porbitals composing the π-system would contain an odd number of nodes. To introduce a node in the orbitals, Heilbronner theorized that a series of p-orbitals could itself be twisted by contortin...

We present a modification of the self-consistent field SCF method of calculating energies of excited states in order to make it applicable to resonance calculations of molecules adsorbed on metal surfaces, where the molecular orbitals are highly hybridized. The SCF approximation is a density-functional method closely resembling standard density-functional theory DFT , the only difference being ...

We introduce an excited state theory for the optimized orbital coupled cluster doubles ~OO-CCD! and valence optimized orbital coupled cluster doubles ~VOO-CCD! models. The equations for transition energies are derived using a similarity transformed Hamiltonian. The effects of orbital relaxation are discussed. We present results for several single-reference molecules (H2O, CH2O, C2H4O, C2H4, BeO...

Figure S1 shows the energetic order of the different terms of Ni2O2 according to the MRCI calculations (without Davidson correction) that use the orbitals from the CASSCF calculations with the smaller active space (8 or 10 orbitals) at the Davidson corrected MRCI minimum structure of the Ag ground term. The other two terms that form the lowest-lying spin ladder together with the ground term are...