▎ 摘　　要

The previous works for twisted bilayer graphene (TBG) are rotated as the center of the "atom" or "ring". Here, we firstly find the other highly symmetrical rotation center, i.e., the "bond", and summarize the Moire pattern rule of the TBG at these three different rotation centers with different angles. It is also found that the TBG can be classified into three structures "a", "r" and "b". Further, by adopting the first principles, we investigate the band structures at three different rotation centers with a certain rotation angle 21.8 degrees, under a perpendicular compressive strain. We find that these three structures share the similar band structure without the strain, exhibiting the linear behavior for the conduction and valence bands. However, the strain breaks this linear behavior and splits the conduction and valence bands for all the structures. The band gap appears for the structure "r", while for the other structures "a" and "b" they are always gapless regardless of the strain. We further provide the corresponding DOS to understand these different behaviors of the band structures for these three structures. Our results may provide a further understanding on the classification of the Moire pattern law of the TBG and the electronic properties of the TBG under the strain.