InN,as an important Ⅲ-nitride,has high electron mobility and low electron effective mass,so it has a wide range of applications in optoelectronic devices,high-frequency high-speed devices,and high-power microwave devices.The Ⅲ-nitrides based dilute magnetic semiconductors (DMSs) can be developed by leveraging the existing fabrication technology for Ⅲ-nitride semiconductor electronic devices,leading to novel semiconductor spintronic devices with a multiplicity of electrical,optical,and magnetic properties.It has been reported that room temperature ferromagnetism exists in InN nanostructures and thin films as well as InN-based DMSs systems.However,the origin mechanism and the formation mechanism of ferromagnetism in these materials have not been fully understood.In Ⅲ-V compound semiconductors,the transition element Mn ions exist mostly in the form of Mn2+ valences while it is also possible for them to emerge in Mn3+ valence states under certain conditions.Although Mn2+ and Mn3+ valance states affect the physical properties of the doped semiconductor differently,there lacks in-depth understanding of such different effects resulting from Mn doping in InN. Under the framework of the density functional theory,in this paper we adopt the generalized gradient approximation (GGA+U) plane wave pseudopotential method to calculate the electronic structure,energy and optical properties of undoped InN and InN doped with three different orderly placeholders of Mn2+ or Mn3+ after geometry optimization.The conducted analysis shows that the system exhibits lower total and formation energies,and improved stability after Mn doping.Manganese doping introduces a spin-polarized impurity band near the Fermi level,and as a result the doped material system has obvious spin polarization.Doping with different valences of Mn ions lead to varying effects on the electronic structure and magnetic property of the material system.The analyses of electronic structure and magnetic property show that both the p-d exchange mechanism and the double exchange mechanism play important roles in the magnetic exchange of the doped system,and Mn3+ doping helps to push the Curie temperature above the room temperature.Comparing with the pure InN,the value of the static dielectric function of the doped system increases significantly.The present analysis concludes that the imaginary part of the dielectric function and the absorption spectrum of the doped system presents strong new peaks in the low-energy region due to the electronic transition associated with the spin-polarized impurity band near the Fermi level. Broadly,this work sheds new light on the microscopic mechanism for the magnetic ordering of Ⅲ-nitride based DMSs,and lays a foundation for developing the novel Ⅲ-nitride based DMSs and devices.