Akm[k_,m_]:=Piecewise[{{A[0, 0], k == 0 && m == 0}, {(-1 + I)*Sqrt[5/7]*A[4, 0], k == 4 && m == -3}, {A[4, 0], k == 4 && m == 0}, {(1 + I)*Sqrt[5/7]*A[4, 0], k == 4 && m == 3}, {(-I/8)*Sqrt[77/3]*A[6, 0], k == 6 && m == -6}, {(1/8 - I/8)*Sqrt[35/3]*A[6, 0], k == 6 && m == -3}, {A[6, 0], k == 6 && m == 0}, {(-1/8 - I/8)*Sqrt[35/3]*A[6, 0], k == 6 && m == 3}, {(I/8)*Sqrt[77/3]*A[6, 0], k == 6 && m == 6}}, 0]