External stress in Souza-Martins Barostat

Dear All,

I wanted apply external stress using Souza-Martin Barostat in forcite simulation as in the literature below ex. pressure of 1 GPa to x and y axis which is equivalent to tensile stress of 0.67 GPa. May I know how to get tensile stress 0.67 in z axis with applied stress of 1 Gpa in x and y axis?

How can i add 1 GP stress in x and y direction, 0.67 in z direction in the below Souza-Martin Barostat box?

Thank you

Hakkim