Structure Of Hydrogen In Metals Research Articles

Stable structure of metallic hydrogen at a pressure of 500 GPa

The structural, electron, phonon, and other characteristics of the metallic normal phase of hydrogen at a pressure of 500 GPa are calculated by an ab initio mathematical simulation. It is shown that metallic hydrogen having a lattice with the I41/amd symmetry is a stable phase at a high hydrostatic compression pressure. The resulting structure has the spectrum of phonons stable with respect to the decay.

Anomalous behavior of atomic hydrogen interacting with gold clusters.

The change in the electronic structure of Au(n)- clusters induced by the exchange of an Au atom by hydrogen is studied using photoelectron spectroscopy. Au anion clusters react with one hydrogen atom but not with molecular hydrogen. The spectra of Au(n)- and Au(n-1)H- clusters show almost identical features for n > 2 suggesting that hydrogen behaves as a protonated species by contributing one electron to the valence pool of the Au(n)- cluster. This behavior is in sharp contrast to that of the commonly understood electronic structure of hydrogen in metals; namely, it attracts an electron from the conduction band of the metal and remains in an "anionic" form or forms covalent bonding. We discuss the influence of the unique electronic structure of H on the unusual catalytic behavior of Au clusters.

A Higher Order Approximation for the Electronic Structure of Hydrogen in Metals

A functional energy difference method based on first principles is used to calculate the electronic contribution to the storage energy of hydrogen impurities in metals. That electronic problem is treated in a higher order approximation which means considering the coupling between one-electron wavefunctions and three-particle amplitudes. A formalism is presented to eliminate all higher order correlations and to reduce the whole system to a one-particle Schrödinger equation with the help of a suitable G reen’s function. The resulting one-electron eigenvalue problem contains some logarithmic singularities due to the fact that there is no gap between occupied and unoccupied electron states in the band structure of a metal. In an electron gas model a convergent theory is reached by an improvement of the Green’s function leading to a screening of the long-range Coulomb potentials. The result is a complicated non-linear algebraic eigenvalue equation which is solved numerically for the special case of a single hydrogen perturbation in a magnesium crystal. The solution shows the influence of higher order electron correlations on the electronic energy eigenvalue of an interstitial hydrogen centre plot as a function of host lattice distortions.

Crystalline structure of metallic hydrogen

The functional-integral approach to the theory of crystals developed earlier is used to compute the type of the crystalline structure of metallic hydrogen. Comparison of the results for a number of crystal lattices shows that in the limit of large pressures and infinitely heavy ions the body-centered structure is preferable.

Positive muon knight shift studies and the electronic structure of hydrogen in metals

An up-to-date review of positive muon Knight shift studies in elemental non-transition and transition metals and in β-Pd hydride is presented. The implications for the local electronic structure of a hydrogen-like impurity are pointed out.

Possibility of a Lifshitz phase transition in Cd observed by a singularity in the muon Knight shift

During the past much effort has been devoted to a systematic study of the muon Knight shiftKμ in metallic environments and its implications on the local electronic structure of hydrogen in metals [1]. These measurements in simple metals were essentially all carried out in polycrystalline samples at room temperature. The present measurements in Cd in polycrystalline and single crystal samples cover a temperature range between 20 K and the melting point of this strongly anisotropic metal (hcp crystal structure,c/a ratio 1.89 — idealc/a ratio 1.63). These measurements add qualitatively new and interesting aspects and insights on the screening of a light hydrogen isotope in a metal as well as on certain properties of the host material itself. The outstanding features of the muon Knight shift in Cd are: (i) a strong intrinsic temperature dependence with an increase ofKμ of more than 100% between 20 K and the melting point (T=593 K), (ii) an anomaly at 110 K in the form of a singularity in the isotropic part ofKμ which is interpreted as a band structure effect, (iii) an anisotropic Knight shift contribution fitting the expressionK(T,θ)=Kiso(T)+Kax(T) * (3 · cos2θ−1)/2, where both, the isotropic and the axial contribution ofKμ, are strongly temperature dependent.

Electronic and elastic structure of hydrogen in metals

The present work consists of an attempt to treat hydrogen in metals on a fundamental level. Starting with the full many-body hamiltonian we derive a one-electron Schrödinger equation. The ground state solution represents the electronic structure of interstitial hydrogen, and the corresponding eigen-value acts as a potential for the proton movement and determines the forces exerted on the neighbouring ions (Kanzaki forces). The self-consistent reaction of the host lattice results in the displacement field and the equilibrium energy. We give as an example the calculation of a single hydrogen atom in magnesium.

Isotope Effect on The Electronic Structure of Hydrogen in Metals

ABSTRACTThe effect of the isotopic mass on the redistribution of electron charge and spin density around a light impurity such as hydrogen in metals has been studied. Considered in this review are: (a) the magnetic hyperfine coupling to the hydrogen nucleus and the effect of isotopic mass, (b) the isotope effect in hydrogen impurity resistivity, (c) the reverse isotope effect in superconducting PdH(D) and (d) the thermally induced detrapping of hydrogen from the vicinity of solute sites in metallic hosts.

Models of electronic structure of hydrogen in metals: Pd-H

Local-density theory is used to study the electron charge-density distribution around hydrogen and host palladium metal atoms. Self-consistent calculations using a finite-size molecular-cluster model based on the discrete variational method are reported. Calculations are also done in a simple "pseudojellium" model to study the electron response to hydrogen within the framework of the density-functional formalism. Results of this simple approach agree very well with the molecular-cluster model. Partial densities of states obtained in the cluster model are compared with band-structure results and conclusions regarding the importance of the local environment on the electronic structure are drawn. Calculated core-level shifts and charge transfer from metal ions to hydrogen are compared with the results of x-ray---photoelectron spectroscopy experiments in metal hydrides and are discussed in terms of conventional anionic, covalent, and protonic models. The effect of zero-point vibration on the electron charge and spin-density distribution is studied by repeating the above calculations for several displaced configurations of hydrogen inside the cluster. The results are used to interpret the isotope effect on the electron distribution around proton and deuteron.

Measurement of the Knight Shift of the Positive-Muon-Spin Rotation Frequency in the Alkali and Alkaline-Earth Series and in Copper

By means of a stroboscopic positive-muon-spin rotation technique, the Knight shift of the local field at positive muons in Na, K, Rb, Cs and Be, Mg, Ca, Sr, Ba and in Cu has been measured to a high precision. The results are discussed in relation to recent theoretical calculations on the local electronic structure of hydrogen in metals.

The influence of the expression for the dielectric function in the calculation of the structure of metallic hydrogen

The influence of the expression for the dielectric function in the calculation of the structure of metallic hydrogen

On the electronic structure of hydrogen in metals

AbstractThe possible electronic structure of hydrogen in ordinary metals and alloys, transitional metals and rare earth metals is discussed, with an emphasis on dilute solutions.