Rod buckling

Hi, colleagues

I'm a new user of comsol and I need to solve a easy task at first: buckling of a rod under pressure.
What kind of solver should I use to get both amplitude and wavelength of undulation? And I would like to compare an deformation energy with different wavelength.
I can make an eigenfrequency analysis and find possible wavelength, but I don't know how to find an amplitude of deformation.