Symmetry can indeed give some criteria. For example, as the teacher upstairs said, parity can usually be used to give. If the inversion center is set between atoms, even parity usually represents a bonded state, and odd parity usually represents an anti-bonded state. This has nothing to do with the specific orbit (spdf), because odd parity means that the probability amplitude of the midpoint is zero, and it must be an anti-bond. This judgment is not absolute, because parity itself depends on norm, not absolute physical quantity. To put it bluntly, for example, an atomic chain, you can set the inversion center on the atom or between atoms, and you just said the latter. In ordered magnetic materials, due to the exchange effect, atomic spins (magnetic moments) are arranged in sequence. If the spins between adjacent atoms are antiparallel due to negative exchange effect, the magnetic moment is in an ordered state (called sequential magnetism), but the total net magnetic moment is still zero when it is not affected by external field. This state of magnetic order is called antiferromagnetism. Note: when a magnetic field is applied to this material, its magnetic moment tends to be arranged along the direction of the magnetic field, that is, the material shows a small positive magnetic susceptibility. However, the magnetic susceptibility is related to temperature and has the maximum value at Nair point. ② Materials made of antiferromagnetic substances with antiferromagnetism as the main magnetic phenomenon are called antiferromagnetic materials. Editing this section of antiferromagnetism in a serious hybrid system, it is meaningless to say bond and anti-bond, because the orbital composition at this time is very complicated. But symmetry (such as parity) is still well defined. The magnetic moment of matter is the sum of the spin of electrons in each atom, the magnetic moment produced by orbital motion and the interaction between atoms. The distribution direction and order of atomic magnetic moments in matter can be determined by using the diffraction phenomenon caused by the action of material magnetic moments on neutron magnetic moments. MnF measured by neutron diffraction? Magnetic moment structure of two antiferromagnetic materials NiO and NiO. In MnF? In antiferromagnetic materials, the magnetic moments of 3d orbital unsaturated electrons of Mn ions magnetized by magnetic field are distributed in the face-centered cubic lattice (1230∶Fcc), because the magnetic moments of the ions are in the same direction at every angle. And the ion magnetic moments in its vertical direction are all in the same opposite direction. The sum of its vectors is equal to zero, so the magnetic susceptibility x of this substance is equal to zero. The orientation effect of a substance in a magnetic field is resisted by thermal excitation, so its magnetic susceptibility changes with temperature. When the temperature is equal to a certain temperature-Neil temperature, the magnetic susceptibility of the antiferromagnetic substance will increase slightly, and when the temperature exceeds the Neil temperature TN, the magnetism of the antiferromagnetic substance is close to paramagnetism.