Modelling a composite wall in ANSYS

Hi,

I am doing a Non-linear Buckling Analysis of a composite wall

I am having hard time modelling the composite wall

The composite wall consists of polystyrene foam as the core element and stucco is applied on either side of the wall.

 There is a thin sheet of mesh embedded in the stucco ( please see the attachment for clear visualization).

Boundary Conditions:Uniform compressive load is applied at the top surface and the bottom surface is fixed

what to calculate: Critical Buckling Load, Critical Buckling Stress 

Can anyone suggest me about the approach to solve this problem?

I have two issues

1. Modelling the composite wall, which element type to choose?

2. The solution is not converging ( convergence issues). what should be done so that the solution converges ?

Any Sugesstions would be highly appreciated.

Regards

Sami