Akm[k_,m_]:=Piecewise[{{0, k == 0 && m == 0}, {I*Sqrt[5/6]*Ma1g, k == 2 && m == -2}, {(1 + I)*Sqrt[5/6]*Ma1g, k == 2 && m == -1}, {(-1 + I)*Sqrt[5/6]*Ma1g, k == 2 && m == 1}, {(-I)*Sqrt[5/6]*Ma1g, k == 2 && m == 2}}, 0]