Symmetry Breaking in the Molecular-Dynamics Method for ab-initio Total-Energy Calculations

摘要

The molecular-dynamics method for performing total-energy calculations offers a number os advantages over conventional matrix-diagonalization techniques in terms of computational speed and memory requirements; it also provides a natural framework for relaxing the atomic configuration. Once the electrons are relaxed close to the ground state, the Hellman-Feynman forces on the atoms can be used to relax the atoms. An analysis of the symmetry of the electron wave functions as they evolve under the molecular-dynamics equation of motion is presented. It is found the symmetry in the initial conditions, corresponding to wave functions of two or more bands being partner functions, can prevent wave functions from converging to eigenfunctions of the Hamiltonian. This artificial symmetry is broken by the Gram-Schmidt orthogonalization procedure so any convenient initial conditions will lead to convergence to eigenstates of the Hamiltonian. Reprints. (aw)