Mechanical results

Dear all,

I did two simulations: one with Forcite (Compass) and one with Discover (Forcite) with the same setting as Forcite . I got mechanical properties for CH (calcium Hydroxide): 50 Gpa from Forcite and 255 Gpa from discover. Anyone can help me the reason of this difference.
My second question is : when we optimize the structure , do we have optimize the cell and does it affect the result of the mechanical properties? Also when we calculate the mechanical properties , there is a check tick for mechanical , I usually leave it on but on the minization tab is OFF . can anyone help me on that please. 

Regards