Energetics of highly kinked steps edges

We have determined the step edge free energy, the step edge stiffness and dimensionless inverse step edge stiffness of the highly kinked < 010> oriented step on a (001) surface of a simple square lattice within the framework of a solid-on-solid model. We have found an exact expression for the step edge free energy in the case that only nearest neighbour interactions are taken into account. At low temperatures the dimensionless inverse step edge stiffness reduces to the universal value 122. However, with increasing temperature the dimensionless inverse step edge stiffness increases. Incorporation of an attractive next-nearest neighbour interaction leads to a suppression of the dimensionless inverse step edge stiffness. For a non-zero next-nearest neighbour interaction the dimensionless inverse step edge stiffness even vanishes at zero temperature.