CHOICE OF MUFFIN-TIN PSEUDOPOTENTIAL

This paper shows that the pseudopotentials of Ziman and Johnson, and Slater's augmented plane-wave potential, are members of a much larger class of pseudopotentials, and proceeds to provide criteria for choosing the pseudopotential most suitable in a given situation. In particular, once the phase shifts have been calculated for the real potential, the radius R in these pseudopotentials is a disposable parameter. A set of rules is proposed for the best choice of R, a matter which is especially important at energies above 1-2 ryd such as are used in low-energy electron diffraction (LEED). One member of this enlarged class of pseudopotentials combines the good convergence properties of the Slater form with the advantage of an angular momentum summation extending over only those values for which the phase shift is non-zero. The convergence, behaviour and misbehaviour, anticipated on theoretical grounds, are demonstrated by numerical calculations.