Abstract
Various point defect configurations have been studied using discrete lattice models. In particular an harmonic reciprocal space model has been used to calculate the lattice distortion around an isolated vacancy in iron, molybdenum and vanadium. The atomic displacements at distances greater than 8a (where 2a is the cube cell side) were in good agreement with the corresponding elasticity results. In addition the binding energies of various divacancy configurations have been calculated. It was found, in all cases, that the pair of vacancies separated by [2,0,0]a was the most stable. The only other stable vacancy pair found was that separated by [3,1,1]a. The displacement field around a vacancy and the binding energies of various divacancy configurations in molybdenum were also studied by minimising the potential energy of the atomic configuration in real space. A pair potential was constructed using spline-fitted cubic polynomials matched to the elastic constant data and the vacancy formation energy. The displacement field around a vacancy was found to be in good agreement with the reciprocal space calculations and the [2,0,0] divacancy was again found to be the most stable, with the [3,1,1] divacancy the only other stable configuration. The migration energy of a single vacancy was also calculated and found to be about 2 eV. In addition the and split interstitial and the crowdion were studied in real space in molybdenum. The formation energies were found to be of the order of 8 eV. Finally, the parameters which define the vacancy and interstitial as point defects in an elastic continuum have been calculated together with the formation volumes.