Akm[k_,m_]:=Piecewise[{{(2*Eeg + 3*Et2g)/5, k == 0 && m == 0}, {Sqrt[14/5]*(Eeg - Et2g), k == 4 && m == -3}, {(7*(-Eeg + Et2g))/5, k == 4 && m == 0}, {Sqrt[14/5]*(-Eeg + Et2g), k == 4 && m == 3}}, 0]