Diamagnetic linear response function

The equivalence between the expressions in Eqs. (6.24) and (6.27) is based on the reformulation of the diamagnetic contribution as a sum-over-states or linear response function. As discussed in Section 5.9 this reformulation is exact, if we are dealing with the exact eigenstates of the unperturbed Hamiltonian. However, in approximate... 

These are again a paramagnetic term, a new diamagnetic-like term and a nuclear contribution, where the first can be expressed as a linear response function according to Eq. (3.114)... 

The reformulation of the diamagnetic contributions to the magnetizability, nuclear magnetic shielding and indirect nuclear spin-spin coupling tensor as linear response functions or sum-over-states (SOS) term discussed in Section 5.9 leads to new operators ... 

As for the magnetizabUity, there are two contributions to the shielding the so-called diamagnetic contribution expectation value (0 1/ 0) and the paramagnetic contribution calculated as a linear response function ((H ... 

Computation of the spin-orbit contribution to the electronic g-tensor shift can in principle be carried out using linear density functional response theory, however, one needs to introduce an efficient approximation of the two-electron spin-orbit operator, which formally can not be described in density functional theory. One way to solve this problem is to introduce the atomic mean-field (AMEI) approximation of the spin-orbit operator, which is well known for its accurate description of the spin-orbit interaction in molecules containing heavy atoms. Another two-electron operator appears in the first order diamagnetic two-electron contribution to the g-tensor shift, but in most molecules the contribution of this operator is negligible and can be safely omitted from actual calculations. These approximations have effectively resolved the DET dilemma of dealing with two-electron operators and have so allowed to take a practical approach to evaluate electronic g-tensors in DET. Conventionally, DET calculations of this kind are based on the unrestricted... 

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