E(k)=E0(k)+E(2)(k) 390n2k2-1k-G hk2 ∑ e 2m gnI∴ E(k)＝E(0) (k)+E(2) (k) 2 2 2 2 2 2 0 2 2 h h G G h k m V m  k k G +   − −     ＝ 