The effect of impurities on the structure and energy of a crystal surface: Mg impurities in calcite as a case study†
A new calculation methodology adopted for the study of crystal surfaces when impurities are present was developed. Moreover, a new way to estimate the surface energy of a doped crystal face was proposed. We have applied the method to study how the structure and energy of the (10.4) crystal face of calcite (CaCO3) are modified when magnesium (Mg2+) impurities are present. In particular, we determined at the empirical level (i) the energy distribution within a (10.4) slab of calcite in which both the percentage and configuration of the Mg2+ ions in the layers forming the slab were varied, and (ii) the surface energy of these Mg-doped slabs. The work methodology described in this paper is extremely versatile and can be applied to the study of any face and crystal. It can be applied to study how vacancies or other point defects affect the structure and energy distribution in a crystal surface. It can also be used to investigate the effect of other impurities (e.g., Mn2+) on the same crystal face, as well as to compare the modifications introduced by the same impurity on different calcite surfaces.