| Despite the tremendous number of theoretical and experimental studies of the electronic properties of the first stage heavy alkali intercalation compounds of graphite: KC(,8), RbC(,8), and CsC(,8), there is still a great deal of uncertainty in the electronic structures of these materials. The electronic structures of these materials--required for the interpretation of experimental results--have been calculated previously by several techniques. Because of the inability of these calculations to satisfactorily resolve the interpretation of experiments, and questions concerning the approximations used in the previous calculations, we attempt to estimate the electronic structure in these materials using a state-of-the-art, self-consistent pseudopotential technique, with a mixed basis of plane waves and localized atomic orbitals. Our goal is to provide a detailed, first principles model of the electronic interactions in these materials that can form the basis for a variety of additional, model calculations that address the experimental issues. In addition, we attempt to elucidate more fully the microscopic basis for differences between the heavy alkali compounds as well as the difference between the heavy alkali compounds as a class and the compounds formed from the light alkali, lithium. As a step toward the first goal, we construct a Fourier expansion model of the electronic structure that includes the states arising primarily from the p(,z) orbitals on carbon as well as the outermost atomic s state on the alkali. From this model we compute densities of states and partial densities of states for the binary compounds. This model is also used to estimate the density of states in a class of ternary compounds of the form: M'(,x)M(,1-x)C(,8), where M' and M are a pair of heavy alkalis. For the binary compounds, we find complete ionization of the alkali atoms and an uneven distribution of the "excess" charge on the carbon planes. Systematic differences in band structures and charge densities are observed and discussed. The model calculation for the ternary compounds leads to additional ideas concerning the experimentally observed anomalies in these systems. |
