Quantum-chemical and lattice-defect hybrid approach to the calculation of defects in metals

A hydrid theoretical approach is presented for the calculation of the properties of localized defects in solids. The method involves treating the electronic structure for the cluster of atoms immediately surrounding the defect from a quantum-mechanical point of view. Specifically, the Hartree-Fock method is employed here with appropriate pseudopotentials for the core electrons. The longer-range elastic distortions of the lattice are treated atomistically using two-body potentials and the lattice-defect method. The total energy of the system, including both the electronic energy of the cluster and the lattice-relaxation energy, is solved selfconsistently. In this paper, the method is applied to a helium interstitial atom in fcc Ni. The hybrid calculations are compared with several two-body lattice-defect calculations as well as with quantum-chemical cluster calculations. The activation energy for diffusion along a 〈110〉 direction is found to be 0. 43 eV which is in reasonable agreement with the 0. 34-eV experimental value of Thomas, Swansiger, and Baskes. The hybrid method eliminates the need to define a two-body interaction between the defect particle and the host atoms while incorporating both electronic redistribution and lattice distortion.