Search results for "chemical bond"

Eight‐Coordinate Endohedral Rhenium, Osmium and Iridium Atoms in Rare‐Earth Halide Cluster Complexes

2010

Endohedral (interstitial) atoms are essential for almost all of the rare-earth halide cluster complexes. Most of these contain octahedral clusters, some are isolated, but the majority exhibits condensation by common edges to structures of higher dimensionality. Higher coordination numbers of the endohedral atoms are rare. Four examples of extended cluster complexes with eight-coordinate endohedral atoms of sixth-period elements (Re, Os, Ir) are presented. In the quasi-isostructural, non-isotypic halides (ReGd 4 )Br 4 and {OsSc 4 }-Cl 4 , square antiprisms of gadolinium and scandium atoms, respectively, are connected by two common faces to chains, surrounded and loosely connected by halogeni…

Synthesis and Structure of Trimethylplatinum(IV) Iodide Complex of 4'-(4-Methoxyphenyl)-2,2':6',2''-terpyridine Ligand and its Halogen Bonding Proper…

2020

Raman spectroscopic study of some lead phosphate glasses with tungsten ions

2006

Abstract The structure of x WO 3  · (100 −  x )[2P 2 O 5  · PbO] glass system with 0 ⩽  x  ⩽ 50 mol% was investigated by Raman spectroscopy. The characteristic bands of these glasses due to the stretching and bending vibrations were identified and analyzed by the increasing of WO 3 content. This fact allowed us to identify the specific structural units which appear in these glasses and thus to point out the network modifier role of tungsten oxide for low concentrations and its former role at high concentrations.

Enantiospecific Response in Cross-Polarization Solid-State Nuclear Magnetic Resonance of Optically Active Metal Organic Frameworks.

2020

We report herein on a NMR-based enantiospecific response for a family of optically active metal-organic frameworks. Cross-polarization of the 1H-13C couple was performed, and the intensities of the 13C nuclei NMR signals were measured to be different for the two enantiomers. In a direct-pulse experiment, which prevents cross-polarization, the intensity difference of the 13C NMR signals of the two nanostructured enantiomers vanished. This result is due to changes of the nuclear spin relaxation times due to the electron spin spatial asymmetry induced by chemical bond polarization involving a chiral center. These experiments put forward on firm ground that the chiral-induced spin selectivity e…

Au Adsorption on Regular and Defected Thin MgO(100) Films Supported by Mo

2007

Using density functional theory we studied systematically a Au atom adsorption on a Mo-supported regular and defected ultrathin MgO film with 1 to 5 ML thickness. On Mo(100) grown regular MgO Au prefers to adsorb at a hollow site instead of an O site found for single-crystal MgO. The metal support also enhances Au adsorption energy in agreement with the earlier theoretical results. Adsorption energy decreases with increasing film thickness being, however, even in the case of 5 ML thick MgO much higher than that on single-crystal MgO. The Bader analysis was performed to estimate the spatial distribution of charge in different cases. The results show charge transfer (0.7−0.8 e) to the Au atom…

Ab initio hybrid DFT calculations of BaTiO3 bulk and BaO-terminated (001) surface F-centers

2017

Using a supercell model and a hybrid B3PW exchange-correlation functional, we have performed first principles calculations for the F-center in the BaTiO3 bulk and on the BaO-terminated (001) surface. We find that two Ti atoms nearest to the bulk F-center are repulsed, while nearest eight oxygen and four barium atoms relax toward the oxygen vacancy (by 1.06, 0.71 and 0.08% of the lattice constant [Formula: see text], respectively). The magnitudes of atomic displacements around the F-center located on the BaO-terminated (001) surface in most cases (except for Ti) are larger than those around the bulk F-center (0.1, 1.4 and 1.0% of [Formula: see text], respectively). Our calculated BaTiO3 bul…

Understanding the optical and bonding properties of hybrid metal-halide (C5H16NP) PbX4 (X = Cl, Br, I) perovskite: A density-functional theory study

2021

Abstract Hybrid perovskites have demonstrated high stability and a promising optoelectronic performance for solar-cells. The quest over their functionalities beyond photo-voltaic applications is currently an important challenge. In this work, we have used density-functional theory to study hybrid perovskites. In particular, we have explored how atomic substitution could be used to design their optoelectronic properties. Under this approach, we have investigated the effect of changing the halogen atom (X  = Cl, Br, I) on the structural, electronic, and optical properties of (C5H16NP) PbX4 hybrid perovskites. The electronic properties have been computed using hybrid functionals including the …

Small radius electron and hole polarons in PbX2 (X = F, Cl, Br) crystals: a computational study

2021

First-principles hybrid density functional theory (DFT) calculations were performed for small radius polarons – self-trapped electrons (STELs) and holes (STHs) in PbX2 (X = F, Cl, Br) crystals, widely used as parent materials for inorganic halide perovskites (CsPbX3) and scintillators. The atomic and electronic structures, spin and charge distributions and formation energies for both types of polarons were predicted for orthorhombic PbF2 and STELs for cubic PbF2. The STH structure was identified in a controversial case of PbCl2. We also confirmed and analyzed in detail experimentally suggested configurations for other cases. It is shown how, due to a delicate balance of ionic and covalent c…

Ab initio calculations of MgF2 (001) and (011) surface structure

2010

We present the results of calculations of surface relaxations, rumplings, and charge distribution for the MgF2 (0 0 1) and (0 1 1) surfaces using ab initio code Crystal-2003 and the hybrid exchange-correlation B3PW functional. These two neutral and polar surfaces show very small relaxation and negligible increase of covalent contribution to the chemical bonding thus remaining considerably ionic. The calculated bulk optical band gap is in a good agreement with the experimental value, whereas optical band gap for the polar (0 1 1) surface is reduced by 0.6 eV compared with the calculated bulk value, in contrast to the (0 0 1) surface gap which remains very close to the bulk.

Ab initio hybrid DFT calculations of BaTiO3, PbTiO3, SrZrO3 and PbZrO3 (111) surfaces

2015

Abstract The results of ab initio calculations for polar BaTiO 3 , PbTiO 3 , SrZrO 3 and PbZrO 3 (111) surfaces using the CRYSTAL code are presented. By means of the hybrid B3LYP approach, the surface relaxation has been calculated for two possible B (B = Ti or Zr) or AO 3 (A = Ba, Pb or Sr) BaTiO 3 , PbTiO 3 , SrZrO 3 and PbZrO 3 (111) surface terminations. According to performed B3LYP calculations, all atoms of the first surface layer, for both terminations, relax inwards. The only exception is a small outward relaxation of the PbO 3 -terminated PbTiO 3 (111) surface upper layer Pb atom. B3LYP calculated surface energies for BaO 3 , PbO 3 , SrO 3 and PbO 3 -terminated BaTiO 3 , PbTiO 3 , …