Akm[k_,m_]:=Piecewise[{{(Ea2u + 2*Eeu)/3, k == 0 && m == 0}, {(((5*I)/3)*(Ea2u - Eeu))/Sqrt[6], k == 2 && m == -2}, {((5/3 + (5*I)/3)*(Ea2u - Eeu))/Sqrt[6], k == 2 && m == -1}, {((-5/3 + (5*I)/3)*(Ea2u - Eeu))/Sqrt[6], k == 2 && m == 1}, {(((-5*I)/3)*(Ea2u - Eeu))/Sqrt[6], k == 2 && m == 2}}, 0]