buckling of a beam clamped at both ends with initial stress applied

Hello,

I'm a newbie using COMSOL v3.4 structural mechanics mode.

I'm simulating a silicon beam (~100 micron long, ~500nm cross-section side) clamped at both ends with initial stress applied (in the MPa range). I drew the model with fixed boundary condition at both sides of the beam, entered the initial normal stress values, and ran the simulation using the structural mechanics mode. I could not get my simulated z-displacement value, which is the beam buckling, at the center of the beam (~0.1nm) to match my experimental data (~500nm) for 20MPa applied.

Has anybody simulated similar structure before? Any suggestions?

Thanks,

Janet