Dear Tsherk :
    Thank you so much for your reply on my pymol question. Your suggestions are helpful to solve the question that has been confused me for so long.
    I still have another related question. After I created the dimmer structure, do you know how to save the new structure as a pdb file? This created pdb file can be opened by the Microsoft word and have roughly twice the amount atom coordinates than the monomer pdb file.
    Once again thank you for your kindly help!