Search results for "Density Functional Theory."
showing 10 items of 935 documents
Regioisomerism in cationic sulfonyl-substituted [Ir(C^N)2(N^N)]+ complexes: its influence on photophysical properties and LEC performance
2016
A series of regioisomeric cationic iridium complexes of the type [Ir(C^N)2(bpy)][PF6] (bpy = 2,2'-bipyridine) is reported. The complexes contain 2-phenylpyridine-based cyclometallating ligands with a methylsulfonyl group in either the 3-, 4- or 5-position of the phenyl ring. All the complexes have been fully characterized, including their crystal structures. In acetonitrile solution, all the compounds are green emitters with emission maxima between 493 and 517 nm. Whereas substitution meta to the Ir-C bond leads to vibrationally structured emission profiles and photoluminescence quantum yields of 74 and 77%, placing a sulfone substituent in a para position results in a broad, featureless em…
Evidence for eight node mixed-symmetry superconductivity in a correlated organic metal
2015
We report a combined theoretical and experimental investigation of the superconducting state in the quasi-two-dimensional organic superconductor $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br. Applying spin-fluctuation theory to a low-energy material-specific Hamiltonian derived from ab initio density functional theory we calculate the quasiparticle density of states in the superconducting state. We find a distinct three-peak structure that results from a strongly anisotropic mixed-symmetry superconducting gap with eight nodes and twofold rotational symmetry. This theoretical prediction is supported by low-temperature scanning tunneling spectroscopy on in situ cleaved single crystals of $\kappa$-(ET)$_2$…
Injection of atoms and molecules in a superfluid helium fountain: Cu and Cu2He(n) (n = 1, ..., ∞).
2011
We introduce an experimental platform designed around a thermomechanical helium fountain, which is aimed at investigating spectroscopy and dynamics of atoms and molecules in the superfluid and at its vapor interface. Laser ablation of copper, efficient cooling and transport of Cu and Cu(2) through helium vapor (1.5 K < T < 20 K), formation of linear and T-shaped Cu(2)-He complexes, and their continuous evolution into large Cu(2)-He(n) clusters and droplets are among the processes that are illustrated. Reflection is the dominant quantum scattering channel of translationally cold copper atoms (T = 1.7 K) at the fountain interface. Cu(2) dimers mainly travel through the fountain unimpeded. How…
Time-domain analysis of electronic spectra in superfluid 4He
2004
Abstract Electronic absorption spectra of impurities in superfluid helium is developed in time domain, using time-dependent density functional theory to describe liquid 4 He and time-dependent perturbation theory to describe the electronic degrees of freedom of the impurity. Angularly isotropic potentials are used to describe the molecule–helium interactions in the ground and excited electronic states. The calculations rationalize experimentally observed phonon side-bands in 4 He droplets and in bulk helium, and allow assignments of spectral features to specific motions of the liquid.
Water interaction with perfect and fluorine-doped Co3O4 (100) surface
2015
Abstract We report the results of theoretical investigations of water adsorption on undoped and fluorine-doped Co3O4 (100) surface by means of the plane-wave periodic density functional theory (DFT) calculations combined with the Hubbard-U approach and statistical thermodynamics. We discuss the effect of fluorine-doping of the Co3O4 (100) surface and calculated oxygen evolution reaction overpotential based on the Gibbs free-energy diagram of undoped and F-doped surfaces.
Ab initiomodeling of surface structure forSrTiO3perovskite crystals
2001
We present and discuss the results of calculations of ${\mathrm{SrTiO}}_{3}$ (100) surface relaxation and rumpling with two different terminations (SrO and ${\mathrm{TiO}}_{2}).$ These are based on ab initio Hartree-Fock method with electron correlation corrections and density functional theory calculations with different exchange-correlation functionals, including hybrid exchange techniques. Both approaches use the localized Gaussian-type basis set. All methods agree well on surface energies and on atomic displacements, as well as on considerable increase of covalency effects nearby the surface. More detailed experiments on surface rumpling and relaxation are necessary for further testing …
Space partitioning of exchange-correlation functionals with the projector augmented-wave method
2018
We implement a Becke fuzzy cells type space partitioning scheme for the purposes of exchange-correlation within the GPAW projector augmented-wave method based density functional theory code. Space partitioning is needed in the situation where one needs to treat different parts of a combined system with different exchange-correlation functionals. For example, bulk and surface regions of a system could be treated with functionals that are specifically designed to capture the distinct physics of those regions. Here, we use the space partitioning scheme to implement the quasi-nonuniform exchange-correlation scheme, which is a useful practical approach for calculating metallic alloys on the gene…
Ab Initio Calculations of Hydroxyl Impurities in CaF2
2012
OH– in CaF2 crystal and the (111) surface have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely, DFT-B3PW. Three bulk and 20 surface OH– configurations ...
Calculations of Surface Structure for SrTiO3 Perovskite
2001
ABSTRACTWe present and discuss results of the calculations for SrTiO3 (100) surface relaxation with different terminations (SrO and TiO2) using a semi-empirical shell model (SM) as well as abinitio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) formalisms. Using the SM, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized. This permits us determination of surface rumpling and surfaceinduced dipole moments (polarization) for different terminations. We also compare results of the ab initio calculations based on both HF with the DFT-type electroncorrelation corrections, several DFT with different exchange-correlation functional…
Calculations of atomic and electronic structure for (100) surfaces of SrTiO3 perovskite
2002
AbstractWe present and discuss main results of the calculations for the surface relaxation and rumpling of SrTiO3 surfaces with TiO2 and SrO terminations using a wide variety of methods of modern computational physics and chemistry, including the shell model (SM) and ab initio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT). The HF and DFT formalisms with different exchange-correlation functionals are implemented into Crystal-98 computer code using a Gaussian-type basis set. We demonstrate that a hybrid B3PW formalism gives the best results for the bulk SrTiO3 properties. Results are compared with previous ab initio plane-wave LDA calculations and LEED experiments. Ou…