We present the results of large scale computer simulations targeted at investigation the phase stability and the structure of symmetric AB diblock copoymers in thin films. The connectivity of the two different monomer species A and B in the diblock copolymer prevents macrophase separation and the molecules assemble into A-rich and B-rich domains on the scale of the molecule's extension. This large length scale of the ordering phenomena makes these polymeric systems a promising candidate for revealing the universal features of self-assembling in amphiphilic molecules. However, the widely spread length and time scales impart protracted long relaxation times to the systems and pose a challenge for computer simulations. Parallel supercomputers like the CRAY T3E are necessary for equilibrating systems with structure on very different length scales. In order to investigate the stability of different phases we quench several systems with identical parameters from the disordered state to a temperature in the intermediate segregation regime and monitor the morphology. Three film thickness are investigated and we find lamellar phases which are parallel and perpendicular oriented lamellar phases. The results are compared to analytical calculations, and the influence of capillary waves on the profiles in the thin film are discussed.
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