Akm[k_,m_]:=Piecewise[{{A[0, 0], k == 0 && m == 0}, {(-I)*B[3, 2], k == 3 && m == -2}, {I*B[3, 2], k == 3 && m == 2}, {Sqrt[5/14]*A[4, 0], k == 4 && (m == -4 || m == 4)}, {A[4, 0], k == 4 && m == 0}, {-(Sqrt[5/11]*A[6, 2]), k == 6 && (m == -6 || m == 6)}, {-(Sqrt[7/2]*A[6, 0]), k == 6 && (m == -4 || m == 4)}, {A[6, 2], k == 6 && (m == -2 || m == 2)}, {A[6, 0], k == 6 && m == 0}}, 0]