<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si78.svg" display="inline" id="d1e1366"> <mml:mi>J</mml:mi> </mml:math> couplings in the solid state from direct energy computations

A simple method for computing J couplings from first principles is proposed, implemented, and tested. In this approach the coupling, which is just the mixed second derivative of the energy with respect to two nuclear magnetic dipoles, is evaluated non-perturbatively by computing the total energy with different fixed dipoles of various orientations, combined in a finite difference scheme. The approach is equally applicable to molecules and solids. Details of the implementation are presented, and a variety of examples in molecules and solids are provided.