Allowance for electron correlation in calculations of the magnetic properties of molecules by variation of the vector potential

Conclusion

The results which we have obtained indicate that when moderately accurate nonperturbed wavefunctions of the electron pairs Ψ^(o) are used, the simplified approach based on Eq. (11) is quite sufficient. The correlation gradient transformations, for which the variables of different electrons are not separated in the function F(r₁, r₂), become important only in precision calculations of the magnetic susceptibilities (for a required accuracy of the order of 0.1% and below), which have to be carried out with extremely accurate nonperturbed wavefunctions Ψ^(o). Finally, it should be remembered that our conclusions apply directly to two-electron systems, described by nodeless nonperturbed coordinated wavefunctions Φ^(o). When the functions Φ^(o) have nodal surfaces (or when the number of electrons in the system is increased), the vector potential variation problem becomes more complicated.