Although the strain in x,y,z direction is useful and would be quite useful for a triangular or rectangular nanowire they pose a small problem when trying to model strain in a circular nanowire. If we look at H. Cui et al “Origin of self-limiting oxidation of Si nanowires” Nanoletters (2008) Vol 8 No. 9 the strain felt by a circular nanowire under thermal oxidation is compressive in the radial direction and tensile in the theta direction and it is not possible to model this strain only using the x,y,z coordinates