Akm[k_,m_]:=Piecewise[{{(Ea1g + 2*(Eeg\[Pi] + Eeg\[Sigma]))/5, k == 0 && m == 0}, {Ea1g - Eeg\[Pi] - 2*Sqrt[2]*Meg, k == 2 && m == 0}, {I*Sqrt[7/5]*(-(Sqrt[2]*Eeg\[Pi]) + Sqrt[2]*Eeg\[Sigma] + Meg), k == 4 && (m == -3 || m == 3)}, {(9*Ea1g - 2*Eeg\[Pi] - 7*Eeg\[Sigma] + 10*Sqrt[2]*Meg)/5, k == 4 && m == 0}}, 0]