Akm[k_,m_]:=Piecewise[{{(Eax2y2 + Eaxy + Eaz2 + Ebxz + Ebyz)/5, k == 0 && m == 0}, {0, (k != 4 && (k != 2 || (m != -2 && m != 0 && m != 2))) || (m != -4 && m != -2 && m != 0 && m != 2 && m != 4)}, {(Sqrt[3]*Ebxz - Sqrt[3]*Ebyz - 4*Maxy2yz2 - (4*I)*Maz2xy + (2*I)*Sqrt[3]*Mb)/(2*Sqrt[2]), k == 2 && m == -2}, {(-2*Eax2y2 - 2*Eaxy + 2*Eaz2 + Ebxz + Ebyz)/2, k == 2 && m == 0}, {(Sqrt[3]*Ebxz - Sqrt[3]*Ebyz - 4*Maxy2yz2 + (4*I)*Maz2xy - (2*I)*Sqrt[3]*Mb)/(2*Sqrt[2]), k == 2 && m == 2}, {(3*Sqrt[7/10]*(Eax2y2 - Eaxy + (2*I)*Max2y2xy))/2, k == 4 && m == -4}, {(3*(Ebxz - Ebyz + Sqrt[3]*Maxy2yz2 + I*Sqrt[3]*Maz2xy + (2*I)*Mb))/Sqrt[10], k == 4 && m == -2}, {(3*(Eax2y2 + Eaxy + 6*Eaz2 - 4*Ebxz - 4*Ebyz))/10, k == 4 && m == 0}, {(3*(Ebxz - Ebyz + Sqrt[3]*Maxy2yz2 - I*Sqrt[3]*Maz2xy - (2*I)*Mb))/Sqrt[10], k == 4 && m == 2}}, (3*Sqrt[7/10]*(Eax2y2 - Eaxy - (2*I)*Max2y2xy))/2]