From the known structure of the diamond the total surface energy of the crystal has been calculated in terms of the energy of the carbonhyphen;carbon bond, and is found to be: 1.50times;10minus;9EBerg cmminus;2for the 111 face, and 2.10times;10minus;9EBerg cmminus;2for the 100 face, whereEBis the energy in ergs per bond. If the bond energy is assumed to be 90 kcal. moleminus;1the values become 5650 erg cmminus;2for the 111 face, and 9820 erg cmminus;2for the 100 face. The corresponding free surface energies are found to be: 111 face at 25deg;=5400 erg cmminus;2100 face at 25deg;=9400 erg cmminus;2. One uncertain feature in the calculation is that involved in the calculation of the decrease in energy caused by the long range binding of the valence bonds in the surfaces. In the 111 face the bonds are 2.517A apart, and are perpendicular to the surface. Thus the bond directions are parallel, while inside the diamond the carbonhyphen;carbon distance is only 1.54A, and the bonds meet head on. While in the 111 face there is only one bond per carbon atom, in the 100 face there are two bonds per atom. In the 111 face there are 1.825times;1015bonds per sq. cmminus;2, with an area of 5.48A2each, while in the 100 face the corresponding values are 3.158times;1015bonds per cm2and 3.167A2per bond. It is concluded that in the 111 face the interaction energy of the type described above is less than one percent and is negligible. Even in the 100 face the interaction should be small. No account was taken of any adjustment of the energy of the unsevered bonds in the surface region. This should cause a greater decrease of energy than the long range binding of the severed bonds. Thus the values of the surface energy calculated in this paper should be considered as maximum values.
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