Akm[k_,m_]:=Piecewise[{{(Ea1p + 2*(Eep + Eepp))/5, k == 0 && m == 0}, {Ea1p - 2*Eep + Eepp, k == 2 && m == 0}, {0, k != 4 || m != 0}}, (3*(3*Ea1p + Eep - 4*Eepp))/5]