r-factor analysis of the effect of non-structural parameters in LEED, applied to Al(111)

A quantitative, r-factor analysis of new experimental LEED data for Al(111) at 90K is presented. The analysis leads to the conclusion that the first interlayer spacing is expanded by 0.9+or-0.5% with respect to the bulk value. A procedure for determination of the optimum values of both structural and nonstructural variables by minimisation of the r factor is described in detail, and evaluated using both simulated and experimental data. The r factor procedure is used to evaluate the consequences for the determination of the first layer spacing d 1 of the choice of values for the non-structural variables, namely the ion-core potential, the inner potential V 0 , the inelastic damping strength V IM , and the Debye temperature theta D . For Al(11) it is found that two selfconsistent ion-core potentials and a truncated atomic potential lead to indistinguishable results as far as the optimum value of d 1 is concerned.