STRUCTURE AND SURFACE ENERGY OF BOTH FLUORITE HALVES AFTER CLEAVING ALONG SELECTED CRYSTALLOGRAPHIC PLANES

The density functional theory, supported with a commercial software, was used to compute the geometry and surface energy of fluorite cleaved along the (111), (110) and (100) planes. In the case of cleaving a piece of fluorite along the (111) plane the two newly created surfaces are identical consisting of fluorite ions with the surface energy equal to 0.384 J/m(2). Cleaving fluorite along the (110) plane also provides identical halves and, both contain one Ca ion next to two F ions, with the surface energy equal to 0.723 J/m(2). When cleaving takes place along the (100) plane, it creates two corresponding halves with different surface structures. One half, having only surface Ca ions (100(Ca)) has the surface energy equal to 0.866 J/m(2), while the surface energy of the second half, having only F surface ions (100(F)), is 0.458 J/m(2). Different structures and energies of the corresponding fluorite surfaces, that is (100(Ca)) and (100(F)) planes, should have an impact on their chemical properties, including hydrophobicity expressed by contact angle. The calculations performed in the paper also showed that reorganization of fluorite surfaces after cleaving was insignificant for all of the investigated planes.