Akm[k_,m_]:=Piecewise[{{Ea/7 + (3*Et1)/7 + (3*Et2)/7, k == 0 && m == 0}, {0, (k == 3 && m == -2) || (k == 3 && m == 2)}, {(-3*Sqrt[5/14]*(2*Ea - 3*Et1 + Et2))/4, k == 4 && (m == -4 || m == 4)}, {(-3*(2*Ea - 3*Et1 + Et2))/4, k == 4 && m == 0}, {(-39*Sqrt[11/35]*Mt)/8, k == 6 && (m == -6 || m == 6)}, {(-39*(4*Ea + 5*Et1 - 9*Et2))/(40*Sqrt[14]), k == 6 && (m == -4 || m == 4)}, {(429*Mt)/(40*Sqrt[7]), k == 6 && (m == -2 || m == 2)}, {(39*(4*Ea + 5*Et1 - 9*Et2))/280, k == 6 && m == 0}}, 0]