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.