- We study lattice reconstruction of tungsten near the Σ3(111) grain boundary (GB) and calculate relaxations of atoms in the vicinity of the Σ3GB in tungsten with and without boron interstitials. Monte Carlo (MC) atomistic simulations have been used to obtain the relaxed configuration of the lattice in the vicinity of the GB. The interacting potentials used in these simulations were obtained by a recursion procedure from nonempirical calculations. We show that boron atoms influence significantly the structure of the lattice in near the tungsten Σ3(111) GB. The displacements of the atoms are determined mainly by W–B and W–W interactions.