Domain-averaged Fermi-hole analysis for solids Baranov, Alexey I; Ponec, Robert; Kohout, Miroslav
The Journal of chemical physics,
2012-Dec-07, Letnik:
137, Številka:
21
Journal Article
Recenzirano
The domain-averaged Fermi hole (DAFH) orbitals provide highly visual representation of bonding in terms of orbital-like functions with attributed occupation numbers. It was successfully applied on ...many molecular systems including those with non-trivial bonding patterns. This article reports for the first time the extension of the DAFH analysis to the realm of extended periodic systems. Simple analytical model of DAFH orbital for single-band solids is introduced which allows to rationalize typical features that DAFH orbitals for extended systems may possess. In particular, a connection between Wannier and DAFH orbitals has been analyzed. The analysis of DAFH orbitals on the basis of DFT calculations is applied to hydrogen lattices of different dimensions as well as to the solids diamond, graphite, Na, Cu and NaCl. In case of hydrogen lattices, remarkable similarity is found between the DAFH orbitals evaluated with both the analytical approach and DFT. In case of the selected ionic and covalent solids the DAFH orbitals deliver bonding descriptions, which are compatible with classical orbital interpretation. For metals the DAFH analysis shows essential multicenter nature of bonding.
We report the high-pressure high-temperature synthesis (P = 15 GPa, T = 1300 K) of BaGe3(tI32) adopting a CaGe3-type crystal structure. Bonding analysis reveals layers of covalently bonded germanium ...dumbbells being involved in multicenter Ba–Ge interactions. Physical measurements evidence metal-type electrical conductivity and a transition to a superconducting state at 6.5 K. Chemical bonding and physical properties of the new modification are discussed in comparison to the earlier described hexagonal form BaGe3(hP8) with a columnar arrangement of Ge3 triangles.
We investigate the evolution of stress fields during the supercontinent cycle using the 2D Cartesian geometry model of thermochemical convection with the non-Newtonian rheology in the presence of ...floating deformable continents. In the course of the simulation, the supercontinent cycle is implemented several times. The number of continents considered in our model as a function of time oscillates around 3. The lifetime of a supercontinent depends on its dimension. Our results suggest that immediately before a supercontinent breakup, the over-lithostatic horizontal stresses in it (referring to the mean value by the computational area) are tensile and can reach −250 MPa. At the same time, a vast area beneath a supercontinent with an upward flow exhibits clearly the over-lithostatic compressive horizontal stresses of 50–100 МРа. The reason for the difference in stresses in the supercontinent and the underlying mantle is a sharp difference in their viscosity. In large parts of the mantle, the over-lithostatic horizontal stresses are in the range of ±25 MPa, while the horizontal stresses along subduction zones and continental margins are significantly larger. During the process of continent-to-continent collisions, the compressive stresses can approximately reach 130 MPa, while within the subcontinental mantle, the tensile over-lithostatic stresses are about −50 MPa. The dynamic topography reflects the main features of the supercontinent cycle and correlates with real ones. Before the breakup and immediately after the disintegration of the supercontinent, continents experience maximum uplift. During the supercontinent cycle, topographic heights of continents typically vary within the interval of about ±1.5 km, relatively to a mean value. Topographic maxima of orogenic formations to about 2–4 km are detected along continent-to-continent collisions as well as when adjacent subduction zones interact with continental margins.
Bi2Pt(hP9) or γ‐Bi2Pt is a high‐temperature modification, which is metastable below 420 °C. We obtained Bi2Pt(hP9) by reducing the layered bismuth subiodide Bi13Pt3I7 with a high excess of ...n‐butyllithium at 70 °C. The crystals endure the heterogeneous reaction and the enormous mass loss. X‐ray diffraction on a small single‐crystal revealed that Bi2Pt(hP9) crystallizes in the acentric trigonal space group P31m (no. 157) with a = 657.30(7) pm and c = 616.65(7) pm. Although structure and stacking of the layers of edge‐sharing PtBi6/3 octahedra resemble the 1H‐polytype of CdI2, Pt–Pt bonding interactions cause distortions that introduce polarity to the structure. Quantum chemical calculations followed by real‐space bonding analysis reveal polar covalent bonding between bismuth and platinum atoms that is not limited to nearest neighbor atoms but is essentially delocalized. The Pt–Pt bond strength in Bi2Pt(hP9) is not much weaker than in the element.
Trigger mechanisms are proposed for gas hydrate decomposition, methane emissions, and glacier collapse in polar regions. These mechanisms are due to tectonic deformation waves in the ...lithosphere–asthenosphere system, caused by large earthquakes in subduction zones, located near the polar regions: the Aleutian arc, closest to the Arctic, and the Antarctica–Chilean and Tonga–Kermadec–Macquarie subduction zones. Disturbances of the lithosphere are transmitted over long distances (of the order of 2000–3000 km and more) at a speed of about 100 km/year. Additional stresses associated with them come to the Arctic and Antarctica several decades after the occurrence of seismic events. On the Arctic shelf, additional stresses destroy the microstructure of metastable gas hydrates located in frozen rocks at shallow depths, releasing the methane trapped in them and leading to filtration and emissions. In West Antarctica, these wave stresses lead to decreases in the adhesions of the covered glaciers with underlying bedrock, sharp accelerations of their sliding into the sea, and fault occurrences, reducing pressure on the underlying rocks containing gas hydrates, which leads to their decomposition and methane emissions.
One-particle reduced density matrix functional theory (1RDMFT) has been applied for the investigation of the real-space picture of the Mott transitions in archetypal hydrogen lattices. The evolution ...of the degree of electron localization during the transition has been evaluated using electron sharing indices for QTAIM atoms, and the connection between the strength of electronic correlation expressed by the 1RDMFT correlation energy and the degree of electron localization has been analyzed at various stages of transition. The spatial decay of the electron sharing indices in the course of transition has also been evaluated and compared with the results obtained for the Hubbard model and finite cluster calculations.
Highly uniform and well-crystallized nanoparticles of the intermetallic compound BiRh were obtained by low-temperature synthesis at 240 °C using the microwave-assisted polyol process. In this time- ...and energy-efficient reaction the polyol acts as solvent, reducing agent, and surfactant, while the microwave radiation leads to fast and homogeneous nucleation and crystal growth. Electron microscopy studies confirmed the presence of pseudohexagonal nanoplates with a primary particle diameter of 60 nm and high crystallinity. As indicated by high-resolution transmission electron microscopy, the plate normal is generally not parallel to 001 but coincides with 421. Powder X-ray diffraction and energy dispersive X-ray spectroscopy revealed the single-phase nature and the equimolar composition. The specific surface area (0.54 m2 g–1) and the particle size distribution were measured by fractional sedimentation. According to the analysis of the chemical bonding by means of quantum chemical calculations, 0.62 electrons are transferred from Bi to Rh. Covalent homoatomic Rh–Rh as well as heteroatomic three-center Rh–Bi–Rh bonds define a three-dimensional bonding network. Unsupported BiRh nanoparticles exhibit an extraordinary high selectivity of 88 to 93% in the semihydrogenation of acetylene, which makes them an interesting model compound as well as a promising candidate for the application as an industrial catalyst.
The article presents the results of an experimental study of the external magnetic field orientation and magnitude influence on the rubidium atomic clock, simulating the influence of the geomagnetic ...field on the onboard rubidium atomic clock of navigation satellites. The tensor component value of the atomic clock frequency light shift on the rubidium cell was obtained, and this value was ~2 Hz. The comparability of the relative light shift (~10−9) and the regular gravitational correction (4×10−10) to the frequency of the rubidium atomic clock was shown. The experimental results to determine the orientational shift influence on the rubidium atomic clock frequency were presented. A significant effect on the relative frequency instability of a rubidium atomic clock at a level of 10−12(10−13) for rotating external magnetic field amplitudes of 1.5 A/m and 3 A/m was demonstrated. This magnitude corresponds to the geomagnetic field in the orbit of navigation satellites. The necessity of taking into account various factors (satellite orbit parameters and atomic clock characteristics) is substantiated for correct comparison of corrections to the rubidium onboard atomic clock frequency associated with the Earth’s gravitational field action and the satellite orientation in the geomagnetic field.
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