Akm[k_,m_]:=Piecewise[{{(Ea1p + 2*(Ee1pp + Ee2p))/5, k == 0 && m == 0}, {Ea1p + Ee1pp - 2*Ee2p, k == 2 && m == 0}, {(3*(3*Ea1p - 4*Ee1pp + Ee2p))/5, k == 4 && m == 0}}, 0]