Hello all, I am attemtping to model crystal twinning using DFT methods. In particular I wish to look at the twin energy as a function of twin angle in a hcp system. I am running into difficulty however in attempting to create my repeat unit prior to my calculations. I was wondering if anybody had some suggestions on how to do this. For example, say I wished to have a twin angle [tex]\theta[/tex] = 30o. How could I go about defining this given a defect free (perfect) bulk crystal. Thanks in advance!!