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处理闭壳层体系的Hartree-Fock能带方法(RHFCO),由于没考虑电子相关效应而不适合于磁性晶体的电子结构计算,这就需要采取超出RHF近似并部分地考虑相关效应的方法,为此,人们提出了“不同自旋采用不同轨道”(DODS)法,实现这个想法的第一步就是去掉轨道双占据近似,并保留单Slater行列式的形式,这样即得到了自旋非限制的Hartree-Fock(UHF)方法,但是单Slater行列式的UHF波函数并不是总自旋S~2算子的本征态(体系哈密顿不显含自旋,故体系能量的本征态也应是自旋S~2的本征态),为了克服这一困难,
The Hartree-Fock banding method (RHFCO), which deals with the closed-shell system, is not suitable for calculating the electronic structure of magnetic crystals without considering the electron-related effects, which requires taking a method that takes into account the RHF approximation and partially considers the correlation effect Therefore, the “different spin using different orbits” (DODS) method has been proposed. The first step to realize this idea is to remove the double occupancy approximation of the orbit and keep the form of a single Slater determinant, thus obtaining a spin-unrestricted Hartree-Fock (UHF) method, but the single Slater determinant UHF wave function is not the eigenstate of the total spin S 2 operator (system Hamiltonian does not contain spin, so the energy eigenstates of the system should also Is the eigenstate of spin S ~ 2). In order to overcome this difficulty,