Akm[k_,m_]:=Piecewise[{{(Ea + Ebxyz + Ebzx2y2 + 2*Ee1 + 2*Ee3)/7, k == 0 && m == 0}, {0, (k != 4 && k != 6 && (k != 2 || m != 0)) || (m != -4 && m != 0 && m != 4)}, {(5*(2*Ea + 3*Ee1 - 5*Ee3))/14, k == 2 && m == 0}, {(3*(-(Sqrt[70]*Ebxyz) + Sqrt[70]*Ebzx2y2 + (2*I)*Sqrt[70]*Mb - (4*I)*Sqrt[42]*MeIm + 4*Sqrt[42]*MeRe))/28, k == 4 && m == -4}, {(3*(6*Ea - 7*Ebxyz - 7*Ebzx2y2 + 2*Ee1 + 6*Ee3))/14, k == 4 && m == 0}, {(3*(-(Sqrt[70]*Ebxyz) + Sqrt[70]*Ebzx2y2 - (2*I)*Sqrt[70]*Mb + (4*I)*Sqrt[42]*MeIm + 4*Sqrt[42]*MeRe))/28, k == 4 && m == 4}, {(-13*(3*Ebxyz - 3*Ebzx2y2 - (6*I)*Mb - (2*I)*Sqrt[15]*MeIm + 2*Sqrt[15]*MeRe))/(10*Sqrt[14]), k == 6 && m == -4}, {(13*(10*Ea + 3*Ebxyz + 3*Ebzx2y2 - 15*Ee1 - Ee3))/70, k == 6 && m == 0}}, (-13*(3*Ebxyz - 3*Ebzx2y2 + (6*I)*Mb + (2*I)*Sqrt[15]*MeIm + 2*Sqrt[15]*MeRe))/(10*Sqrt[14])]