Coupled cluster investigation on the low-lying electronic states of CuCN and CuNC and the ground state barrier to isomerization

Spectroscopy of YO from first principles

We report an ab initio study on the spectroscopy of the open-shell diatomic molecule yttrium oxide, YO. The study considers the six lowest doublet states, X2Σ+, A'2Δ, A2Π, B2Σ+, C2Π, D2Σ+, and a few higher-lying quartet states using high levels of electronic structure theory and accurate nuclear motion calculations. The coupled cluster singles, doubles, and perturbative triples, CCSD(T), and multireference configuration interaction (MRCI) methods are employed in conjunction with a relativistic pseudopotential on the yttrium atom and a series of correlation-consistent basis sets ranging in size from triple-ζ to quintuple-ζ quality. Core-valence correlation effects are taken into account and complete basis set limit extrapolation is performed for CCSD(T). Spin-orbit coupling is included through the use of both MRCI state-interaction with spin-orbit (SI-SO) approach and four-component relativistic equation-of-motion CCSD calculations. Using the ab initio data for bond lengths ranging from 1.0 to 2.5 Å, we compute 6 potential energy, 12 spin-orbit, 8 electronic angular momentum, 6 electric dipole moment and 12 transition dipole moment (4 parallel and 8 perpendicular) curves which provide a complete description of the spectroscopy of the system of six lowest doublet states. The Duo nuclear motion program is used to solve the coupled nuclear motion Schrödinger equation for these six electronic states. The spectra of 89Y16O simulated for different temperatures are compared with several available high resolution experimental studies; good agreement is found once minor adjustments are made to the electronic excitation energies.

Electronic, bonding, and optical properties of 1d [CuCN]n (n = 1-10) chains, 2d [CuCN]n (n = 2-10) nanorings, and 3d [Cun (CN)n ]m (n = 4, m = 2, 3; n = 10, m = 2) tubes studied by DFT/TD-DFT methods

The electronic, bonding, and photophysical properties of one-dimensional [CuCN](n) (n = 1-10) chains, 2-D [CuCN](n) (n = 2-10) nanorings, and 3-D [Cu(n)(CN)(n)](m) (n = 4, m = 2, 3; n = 10, m = 2) tubes are investigated by means of a multitude of computational methodologies using density functional theory (DFT) and time-dependent-density-functional theory (TD-DFT) methods. The calculations revealed that the 2-D [CuCN](n) (n = 2-10) nanorings are more stable than the respective 1-D [CuCN](n) (n = 2-10) linear chains. The 2-D [CuCN](n) (n = 2-10) nanorings are predicted to form 3-D [Cun (CN)(n)](m) (n = 4, m = 2, 3; n = 10, m = 2) tubes supported by weak stacking interactions, which are clearly visualized as broad regions in real space by the 3D plots of the reduced density gradient. The bonding mechanism in the 1-D [CuCN](n) (n = 1-10) chains, 2-D [CuCN](n) (n = 2-10) nanorings, and 3-D [Cu(n)(CN)(n)](m) (n = 4, m = 2, 3; n = 10, m = 2) tubes are easily recognized by a multitude of electronic structure calculation approaches. Particular emphasis was given on the photophysical properties (absorption and emission spectra) of the [CuCN](n) chains, nanorings, and tubes which were simulated by TD-DFT calculations. The absorption and emission bands in the simulated TD-DFT absorption and emission spectra have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made.