Dingle temperatures and Fermi surface changes in Cu(H): an application of the impurity cluster formalism

The impurity cluster formalism has been extended to describe the scattering of Bloch electrons by a cluster centred around an interstitial impurity. An important feature of this extension is that the host wavefunction coefficients and Green function at the interstitial site can be obtained numerically from their values at the next-neighbouring atoms. The theory has been applied to Cu(H). Calculations of Dingle temperatures x* and cross-sectional area changes delta A reveal that x* is mainly determined by the hydrogen potential, whereas delta A is additionally sensitive to the environment of the hydrogen. The experimental x* values can be nicely reproduced simulating screening effects by means of a potential shift. Charge neutrality is achieved satisfactorily using a seven-atom cluster which means that the influence of H is not restricted to its own muffin-tin sphere. Because of the sensitivity of delta A to charge transfer the merits of the potentials available can be judged to their full extent only if this quantity is measured as well. The effect of lattice distortion around H appears to be very small. Comparison of calculated and measured anisotropy of x* confirms that the hydrogen occupies the octahedral and not the tetrahedral interstice in Cu.