Electric field gradient effects on magnetic susceptibility

A general expression for the magnetic susceptibility of a molecule in the presence of a timeindependent, spatially uniform magnetic field, and a non-uniform electric field with a uniform gradient is discussed. The molecular response can be described by magnetic susceptibility polarizability tensors that depend on the choice of the origin for the coordinate system to which they are referred. However, the orbital magnetic dipole moment induced by the perturbation and the interaction energy are invariant to a change to the origin of the coordinate system and to the related gauge transformation. Theoretical estimates of the induced magnetic dipole moment obtained via single-origin methods are translationally invariant only for optimal variational wavefunctions. Common origin approaches relying on the algebraic approximation yield predictions that depend on the first, second, and third power of the origin shift. Distributed origin methods depend at most on the square of the shift.