Akm[k_,m_]:=Piecewise[{{(Ea1g + 2*(Eeg1 + Eeg2))/5, k == 0 && m == 0}, {Ea1g + Eeg1 - 2*Eeg2, k == 2 && m == 0}, {(3*I)*Sqrt[7/5]*Meg, k == 4 && (m == -3 || m == 3)}, {(3*(3*Ea1g - 4*Eeg1 + Eeg2))/5, k == 4 && m == 0}}, 0]