RECIPROCITY THEOREMS AND PSEUDOELECTRIC FIELDS FOR AB-INITIO FORCE CALCULATIONS

We present a method for constructing a pseudoelectric field at each pa int in space, which gives the force on a classical ion due to its loca l or nonlocal pseudopotential interaction with a quantum electronic sy stem. Our derivation extends a classical reciprocity theorem used by H ellmann and Feynman for purely Coulombic interactions to a family of g eneralized electron-ion potentials, which are useful for efficient ele ctronic structure studies. The method is computationally efficient and it should be particularly useful for structural relaxation and molecu lar dynamics studies of complex systems.