Akm[k_,m_]:=Piecewise[{{(Ea2u + 3*(Et1u + Et2u))/7, k == 0 && m == 0}, {(-1/2 + I/2)*Sqrt[5/7]*(2*Ea2u - 3*Et1u + Et2u), k == 4 && m == -3}, {(2*Ea2u - 3*Et1u + Et2u)/2, k == 4 && m == 0}, {(1/2 + I/2)*Sqrt[5/7]*(2*Ea2u - 3*Et1u + Et2u), k == 4 && m == 3}, {((-13*I)/60)*Sqrt[11/21]*(4*Ea2u + 5*Et1u - 9*Et2u), k == 6 && m == -6}, {((13/12 - (13*I)/12)*(4*Ea2u + 5*Et1u - 9*Et2u))/Sqrt[105], k == 6 && m == -3}, {(26*(4*Ea2u + 5*Et1u - 9*Et2u))/105, k == 6 && m == 0}, {((-13/12 - (13*I)/12)*(4*Ea2u + 5*Et1u - 9*Et2u))/Sqrt[105], k == 6 && m == 3}, {((13*I)/60)*Sqrt[11/21]*(4*Ea2u + 5*Et1u - 9*Et2u), k == 6 && m == 6}}, 0]