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