Universal lower bounds on the kinetic energy of electronic systems with noncollinear magnetism

TL;DR

This paper establishes universal lower bounds on the kinetic energy densities in electronic systems with noncollinear magnetism, extending density functional theory to include complex spin and current densities.

Contribution

It generalizes von Weizsäcker's lower bound to systems with noncollinear spin and current densities, providing new theoretical limits for kinetic energy in such systems.

Findings

Proves lower bounds for kinetic energy densities in many-electron systems.

Shows these bounds depend on electron, spin, and current densities.

Extends density functional theory to noncollinear magnetic systems.

Abstract

The distribution of noncollinear magnetism in an electronic system provides information about the kinetic energy as well as some kinetic energy densities. Two different everywhere-positive kinetic densities related to the Schr\"odinger--Pauli Hamiltonian are considered. For one-electron systems described by a single Pauli spinor, the electron density, spin density and current density completely determines these kinetic energy densities. For many-electron systems, lower bounds on the kinetic energy densities are proved. These results generalize a lower bound due to von Weizs\"acker, which is based on the electron density alone and plays an important role in density functional theory. The results have applications in extensions of density functional theory that incorporate noncollinear spin densities and current densities.