First principles investigation of the electronic structure of La2MnNiO6: A room-temperature insulating ferromagnet

Using first principles calculations within DFT based on the full potential APW+lo method, we calculated the electronic and magnetic structures for the ferromagnetic and antiferromagnetic states of La2MnNiO6 and analyzed the site projected density of states and electronic band structures. Our calculations show that the ground state of La2MnNiO6 is ferromagnetic insulating with the magnetization in agreement with Hund's first rule and experimental findings.Comment: 10 pages, 3 figure

Structure and electronic properties of new model dinitride systems: A density-functional study of CN2, SiN2, and GeN2

The dinitrides CN2, SiN2, and GeN2 in assumed pyrite-type structures are studied by means of density functional theory using both ultrasoft pseudopotentials and the augmented spherical wave (ASW) method. The former two materials constitute the large-x limit of the broader class of CNx and SiNx compounds, which are well known for their interesting mechanical and electronic properties. For CN2 a large bulk modulus B_0 of 405 GPa was determined . While SiN2 is found to be a wide band gap compound, the calculated gaps of CN2 and GeN2 are considerably smaller. The trends in structural and electronic properties as e.g. bond lengths, band gaps and covalency are well understood in terms of the interplay of different types of bonding.Comment: 9 pages, 5 figure

Molecular and all solid DFT studies of the magnetic and chemical bonding properties within KM[Cr(CN)6_6] (M = V, Ni) complexes

A study at both the molecular and extended solid level in the framework DFT is carried out for KM[Cr(CN)$_6$] (M = V, Ni). From molecular calculations, the exchange parameters J are obtained, pointing to the expected magnetic ground states, i.e., antiferromagnetic for M = V with J = -296.5 cm$^{-1}$ and ferromagnetic for M = Ni with J = +40.5 cm$^{-1}$. From solid state computations the same ground states and J magnitudes are confirmed from energy differences. Furthermore an analysis of the site projected density of states and of the chemical bonding is developed in which the cyanide ion linkage is analyzed addressing some isomerism aspects.Comment: new results, 5 tables, 7 fig

Joint stereochemical and ab initio overview of SnII electron lone pairs (E) and F−(E) triplets effects on the crystal networks, the bonding and the electronic structures in a family of tin fluorides

The stereochemistry of 5s2 (E) lone pair of divalent Sn (SnII designated by M*) and the lone pair triplet around the fluorine ions are examined complementarily with stereo-chemical approach and ab initio quantum investigations focusing on the electron localization and pertaining electronic structure properties, obtained within Density Functional Theory (DFT) and derived Electron Localization Function (ELF) mapping. The review completes a series of former ones focusing on the stereochemical role played by electron lone pairs LP. We start by examining LP-free SnIVF4 then develop on SnIIF2E in its three crystal varieties (α, β, γ). The investigation then extends to study two mixed-valence fluorides: Sn2IISnIVF6E2 and SnIISnIVF6E. The lone pair presence is readily detected in the crystalline network by its sphere of influence characterized by a radius rE, and M*-E directions; all distances are also detailed and assessed. The observations point to significant modifications of the structure which are also analyzed with the electronic density of states DOS projected over the different atomic constituents. Within the selected fluorides details of SnII various coordination numbers (CN) generally indicate one-sided coordination; specifically: CN = 4 + 1 SnF4E triangular bipyramid, CN = 5 + 1 SnF5E distorted octahedron (square pyramid with E roughly symmetric of its F apex) and CN = 6 octahedron [SnE]F6. In the latter, the rotation speed of E (which increases with Z number due to relativistic effects) and the size of the F polyhedron make it favorable enough to E rotating around Sn2+ with the particularity of its transformation into a large cation [SnE]2+ with a size comparable to Ca2+, Sr2+ or Ba2+

In search of new candidates for ultra-hard materials: the ternary BC₃N₃ stoichiometry

Starting from formerly investigated graphitic like C3N4, selective substitution of nitrogen with boron led to model structures for the experimentally observed BC3N3 stoichiometry. Investigations of the geometry optimisation and of the electronic properties were carried out using pseudo potential and full potential computations in the framework of the local density functional theory for the two and three dimensional structures (2D and 3D). They lead to propose a precursor (2D), a β-structure and a new ultra hard rhombohedral compound with a hardness (B0358 GPa) that reaches the range of formerly studied BC2N structures built from hexagonal and cubic diamond

A model study for the breaking of N2 from CNx within DFT

A hypothetical CN2 structure was investigated as a model to study the release of N2 from the octahedral hole of 3D carbon based ultra hard compounds, which is the most important drawback in the attempts to synthesize ultra hard compounds like C3N4 and C11N4. Full structure relaxations using DFT methods led to a structure at the energy minimum showing a significantly enlarged N---N distance of 1.34 Å compared to the molecular N2 (1.09 Å). While for small volume changes a high hardness for CN2 of 405 GPa is calculated, we found that enlargements of the cell constant lead to the release of N2 that could be followed calculating the ELF and the charge transfer within the AIM theory. The whole procedure simulates an inverted “harpoon mechanism”

Potential new candidates for hard materials within the ternary XC₃N₃ (X = B, Al, Ga) stoichiometry

Starting from formerly investigated graphitic like C3N4, selective substitution of nitrogen with boron led to model structures for the experimentally observed BC3N3 stoichiometry. Similar investigations were extended to the 2nd- and 3rd-period elements Al and Ga. Geometry optimisation and studies of the electronic properties were carried out using the pseudo-potential (VASP) method in the framework of the local density functional theory for the two and three dimensional structures (2D and 3D). They respectively lead to propose a precursor (2D), a β-structure and new ultra hard materials (3D), with hardness (B0 358 GPa) for BC3N3 and (B0 325 GPa) for AlC3N3 for the high-pressure phases

Electronic structure of intercalated metal disulfide (Fe1/4TiS2) studied by XPS and theoretical calculations

International audienceThe specific crystallographic features of Fe1/4TiS2 have led us to carry out an experimental (X-ray photoelectron spectroscopy) and theoretical (augmented spherical wave method) study to shed light on the different chemical environments of atoms in the structure and their host-guest interaction. The chemical shifts or/and broadening of the core-level peaks have been correlated with initial and final states, the former based on the charge transfer between the iron intercalant and the host titanium atoms. The valence band is modified by the intercalant, primarily towards low binding energies. The electronic structure calculations are in good agreement with the observed spectra. © 1997 Elsevier Science B.V

Electronic structure of intercalated metal disulfides (Ag1/3TiS2 and Fe1/3TiS2) studied by XPS and theoretical calculations

International audienceThe effect of metal intercalation (silver and iron) into 1T-CdI2-type TiS2 layered crystals, expressed as MxTiS2, has been studied by X-ray photoelectron spectroscopy (XPS) and self-consistent electronic calculations (augmented sphere wave method). The spectra are found to depend strongly on the guest metals, and we have shown how the XPS valence bands are modified by the 'host-guest' interactions by using calculated densities of states. In the first approximation, the chemical shift of the core peaks are correlated with Mulliken population analysis