Energy band 4,(a)-ek4,(O) u,(a-e4,0)=-0 4'(a)-ea4'(0)42'(a-ekau2'(0) 4(a4,(a)-4'(a,(a-4(a,(O)+4O4,(aa +e2au(O)h4,0)-u'0hu,(0)】+u'(a4,(0)+u'(0h4,(ala=0 U-U2 264242-4,4） cos Ka, whereU=u O)uz(a)+u(a)uz(0). U2=4,(04(a+42(a)4(O)Energy band           0     0 where 0 0 , cos , 2 ' 2 1 ' 2 2 1 ' 1 2 ' 1 1 2 ' 2 1 ' 1 2 1 2 U u u a u a u U u u a u a u Ka u u u u U U                        0 ' - ' 0 ' - ' 0 - 0 - 0 1 1 2 2 1 1 2 2  u a e u u a e u u a e u u a e u iKa iKa iKa iKa                    0 0 '0 0  '  0 '0   0 ' 0 0 1 2 1 2 1 2 ' 1 2 2 ' 1 2 ' 1 2 1 2 ' 1 2         i K a iKa iKa e u u u u u a u u u a e u a u a u a u a u a u u u a e