Geometric Formulation of Unique Quantum Stress Fields
  We present a derivation of the stress field for an interacting quantum system within the framework of local density functional theory. The formulation is geometric in nature and exploits the relationship between the strain tensor field and Riemannian metric tensor field. The resultant expression obtained for the stress field is gauge-invariant with respect to choice of energy density, and therefore provides a unique, well-defined quantity. To illustrate this formalism, we compute the pressure field for two phases of solid molecular hydrogen. 
Christopher L. Rogers, Andrew M. Rappe