Akm[k_,m_]:=Piecewise[{{(Eappxy + Eappxz + Eapx2 + Eapy2z2 + Eapyz)/5, k == 0 && m == 0}, {0, (k != 2 && k != 4) || (k != 4 && m != -2 && m != -1 && m != 0 && m != 1 && m != 2) || (m != -4 && m != -3 && m != -2 && m != -1 && m != 0 && m != 1 && m != 2 && m != 3 && m != 4)}, {(Sqrt[6]*Eappxz + Sqrt[6]*Eapx2 - Sqrt[6]*Eapy2z2 - Sqrt[6]*Eapyz + 2*Sqrt[2]*Mapy2z2x2)/4, k == 2 && (m == -2 || m == 2)}, {(I/2)*(Sqrt[6]*Mappxzxy - 2*Sqrt[2]*Mapx2yz), k == 2 && (m == -1 || m == 1)}, {(-2*Eappxy + Eappxz - Eapx2 + Eapy2z2 + Eapyz + 2*Sqrt[3]*Mapy2z2x2)/2, k == 2 && m == 0}, {(-3*Sqrt[7/10]*(4*Eappxy - 3*Eapx2 - Eapy2z2 + 2*Sqrt[3]*Mapy2z2x2))/8, k == 4 && (m == -4 || m == 4)}, {((3*I)/4)*Sqrt[7/5]*(2*Mappxzxy + Sqrt[3]*Mapx2yz - Mapy2z2yz), k == 4 && (m == -3 || m == 3)}, {(3*(4*Eappxz - 3*Eapx2 + 3*Eapy2z2 - 4*Eapyz - 2*Sqrt[3]*Mapy2z2x2))/(4*Sqrt[10]), k == 4 && (m == -2 || m == 2)}, {(((-3*I)/4)*(2*Mappxzxy + Sqrt[3]*Mapx2yz + 7*Mapy2z2yz))/Sqrt[5], k == 4 && (m == -1 || m == 1)}}, (3*(4*Eappxy - 16*Eappxz + 9*Eapx2 + 19*Eapy2z2 - 16*Eapyz + 10*Sqrt[3]*Mapy2z2x2))/40]