Akm[k_,m_]:=Piecewise[{{(Ea1g + 2*(Eeu1 + Eeu2))/5, k == 0 && m == 0}, {Ea1g + Eeu1 - 2*Eeu2, k == 2 && m == 0}, {-3*Sqrt[7/5]*Meu, k == 4 && m == -3}, {(3*(3*Ea1g - 4*Eeu1 + Eeu2))/5, k == 4 && m == 0}, {3*Sqrt[7/5]*Meu, k == 4 && m == 3}}, 0]