In this work we study a set of <1 1 0 > tilt grain boundaries (GB) with a misorientation angle varied from 26 to 141 degrees by applying atomistic calculations in alpha-Fe. A set of different interatomic potentials was used to deduce the most energetically favourable configurations, the gamma surface profile and sliding pathway. The uniaxial loading tests were performed by pulling apart two grains to calculate the separation energy profile, cleavage stress and to study the process of the formation of free surfaces during the simulated cleavage fracture. We show that the resistance of a grain boundary to slide is closely related to its structure. The results of the loading tests have shown that the cleavage fracture process may involve: (i) reconstruction of the surface and/or formation of two non-equivalent open surfaces; (ii) movement of the grain boundary front, which involves sliding and thus allows to accommodate the applied strain by plastic deformation.