RECURSION METHOD SOLUTION OF COHERENT-POTENTIAL APPROXIMATION EQUATIONS - APPLICATION TO SURFACE ALLOYS

We present a new method of solving the self-consistent field equations in the coherent-potential approximation (CPA). In our approach, the c oherent potential and the Green function of the effective medium are r epresented as continued fractions. If is shown that, contrary to the s tandard CPA method, it is possible to define an energy-independent Ham iltonian, which acts in an augmented space, so that the recursion meth od can be directly used. The continued-fraction expansion of the Green function is taken until the desired accuracy is achieved and the dens ity of states is calculated using the appropriate terminator. The meth od is directly applicable to an alloy surface and no further approxima tions other than the CPA are introduced. In particular, the method avo ids the main difficulty of the standard CPA approach, i.e. the solutio n of coupled CPA equations for each energy point. First applications o f the method to different alloy surfaces are presented.