Akm[k_,m_]:=Piecewise[{{(Ea2u + 3*(Et1u + Et2u))/7, k == 0 && m == 0}, {-(Sqrt[5/14]*(2*Ea2u - 3*Et1u + Et2u)), k == 4 && m == -3}, {(2*Ea2u - 3*Et1u + Et2u)/2, k == 4 && m == 0}, {Sqrt[5/14]*(2*Ea2u - 3*Et1u + Et2u), k == 4 && m == 3}, {(13*Sqrt[11/21]*(4*Ea2u + 5*Et1u - 9*Et2u))/60, k == 6 && (m == -6 || m == 6)}, {(13*(4*Ea2u + 5*Et1u - 9*Et2u))/(6*Sqrt[210]), k == 6 && m == -3}, {(26*(4*Ea2u + 5*Et1u - 9*Et2u))/105, k == 6 && m == 0}, {(-13*(4*Ea2u + 5*Et1u - 9*Et2u))/(6*Sqrt[210]), k == 6 && m == 3}}, 0]