Abstract
The static lattice distortion and relaxation energy for nitrogen and oxygen interstitials at octahedral and tetrahedral sites in niobium, tantalum and vanadium have been calculated by using the Green function method for lattice statics. The forces responsible for the lattice distortion have been obtained from the measured values of the dipole tensor, which avoids the need for a priori knowledge of the gas-host potential. However, simple functions for the 'effective' gas-host interaction have been fitted to the calculated values of the atomic displacements which should be useful for further calculations on these systems.