Akm[k_,m_]:=Piecewise[{{(Eapp + Eapx + Eapy)/3, k == 0 && m == 0}, {0, k != 2 || (m != -2 && m != 0 && m != 2)}, {(5*(Eapx - Eapy + (2*I)*Mapxy))/(2*Sqrt[6]), k == 2 && m == -2}, {(5*(2*Eapp - Eapx - Eapy))/6, k == 2 && m == 0}}, (5*(Eapx - Eapy - (2*I)*Mapxy))/(2*Sqrt[6])]