解答

(1) eA = 2t, eB = 0, eC = 0, eD = -2t 

(2) UAA = UAB = ... = U/4, JAB = JBC = ... = U/4 

(3) 0  

(4) U/2

(5) Y'がU/4だけ低い 

(6) <Y|H|Y'> = U/4, <Y|H|Y"> = 0, <Y'|H|Y"> = 0 

(7) 差がなくなる