| We use the shadow wave function formalism to determine the energy of formation of single and double vacancies in 4He crystals at T = 0 K. Data is presented for both the bcc and hcp phases. The activation energy for a single vacancy in bcc 4He is found to be about 50% of that in hcp 4He, which is approximately 15.6 K. By determining the occupation of the Voronoi regions around the crystal sites, we determine the location of vacancies in the crystal and study the relaxation of the neighboring atoms. We also present data on the correlations between vacancies, and between vacancies and 3He impurities. Following the position of the vacancy through successive configurations we study the motion of the vacancy as seen in our Monte Carlo simulations. On the shorter Monte Carlo time scales, we observe greater vacancy motion in the bcc phase than in the hcp phase.; An existing dynamical quantum many-body theory of charge transfer, previously used to describe atoms with simple s-orbitals, such as alkalis and alkaline-earths in-teracting with metal surfaces, is generalized to describe atoms with richer orbital structures. In this model the many-body equations of motion (EOM) are developed systematically as an expansion in the number of surface particle-hole excitations. In the simplest version of the model, only the single-particle pz-orbitals of the atom, the ones oriented perpendicular to the surface, participate directly in resonant charge transfer as they have the largest overlap with the metallic wavefunctions. However, as the several-electron Russell-Sanders eigenstates, labeled by total angular momenta quantum numbers J, L, and S, are built out of products of single-particle orbitals, the relevant matrix elements must be incorporated into the many-body EOM's. Comparison to recent experimental results on the scattering of low-energy oxygen ions off Cu(001) surfaces is made. |
