Simultaneous Relaxation of Nuclear Geometries and Electric Charge Densities in Electronic Structure Theories

A simple formalism is presented, within the density-functional approach, which constitutes a powerful scheme for directly calculating the ground-state energy of systems with arbitrarily located nuclei and their accompanying electrons. The method permits simultaneous relaxation of both the atomic geometries and the electronic charge densities of polyatomic systems towards equilibrium. It circumvents the far less efficient indirect (consecutive) approach in which the equilibrium geometry is determined after calculation of energies on the Born-Oppenheimer surface.