Magnetic ground state and spin waves in A(AÂ =Â K, Rb or Cs)Fe1.5Se2

► We have obtained the ground state phase diagram of the J1-J2 Heisenberg model. ► The A-collinear antiferromagnetic phase is stable for AFe1.5Se2. ► Spin wave and dynamic structure factor are investigated with the spin wave theory. ► The obtained dynamic structure factor can offer some guidance for future experiments.