Measuring orbital interaction using quantum information theory

Quantum information theory gives rise to a straightforward definition of the interaction of electrons Ip,q in two orbitals p,q for a given many-body wave function. A convenient way to calculate the von Neumann entropies needed is presented in this work, and the orbital interaction Ip,q is successfully tested for different types of chemical bonds. As an example of an application of Ip,q beyond the interpretation of wave functions, Ip,q is then used to investigate the ordering problem in the density-matrix renormalization group.