Akm[k_,m_]:=Piecewise[{{(Ea1 + Eb1 + Eb2)/3, k == 0 && m == 0}, {0, k != 2 || (m != -2 && m != 0 && m != 2)}, {(5*(Eb1 - Eb2))/(2*Sqrt[6]), k == 2 && (m == -2 || m == 2)}}, (5*(2*Ea1 - Eb1 - Eb2))/6]