Analytic Formulas for the Orientation Dependence of Step Stiffness and   Line Tension: Key Ingredients for Numerical Modeling
  We present explicit analytic, twice-differentiable expressions for the temperature-dependent anisotropic step line tension and step stiffness for the two principal surfaces of face-centered-cubic crystals, the square {001} and the hexagonal {111}. These expressions improve on simple expressions that are valid only for low temperatures and away from singular orientations. They are well suited for implementation into numerical methods such as finite-element simulation of step evolution. 
T. J. Stasevich and T. L. Einstein