Method for calculating surface electronic structure of noble and transition metals

We present a new method for the calculation of the electronic structure of noble and transition-metal surfaces that is based upon the linear combination of muffin-tin orbitals (LCMTO) technique. We adopt the by now common technique of using film calculations to accurately simulate the electronic structure at the surface of bulk $d$-band metals. A central feature of our method is the introduction of a new basis consisting of (a) muffin-tin orbitals plus (b) additional functions we call "plane-wave orbitals," which are constructed from the exact solutions of Schrödinger's equation in the regions exterior to the film. This method has the virtue of being able to treat non-muffin-tin potentials, yet reproduces, in the limit of a muffin-tin potential, exactly the same results as the more conventional film Green's-function method of Kar and Soven and of Kohn. This parallels the relationship of the bulk LCMTO method to the Korringa-Kohn-Rostoker method, and we conclude, therefore, that our method is the proper generalization (for films) of the bulk LCMTO technique. We also outline a linearization scheme, based on one successfully used in recent bulk LCMTO calculations, to achieve the computational speed necessary for self-consistent film calculations.