Solid angle is much, much farther away. The solid angle subtended by the complete ()-dimensional spherical surface of the unit sphere in -dimensional Euclidean space can be defined in any number of dimensions . One often needs this solid angle factor in calculations with spherical symmetry. It is given by the formula where is the gamma function. When is an integer, the gamma function can be computed explicitly. It follows that This gives the expected results of 4 steradians for the 3D sphere bounded by a surface of area and 2 radians for the 2D circle bounded by a circumference of length
Surface energy number of atoms at the surface and in the bulk of the solid. Calculating the surface formation energy of a crystalline solid In density functional theory, surface energy can be calculated from the following expression where formula_17 is the total energy of surface slab obtained using density functional theory. formula_18 is the number of atoms in the surface slab. formula_19 is the bulk energy per atom. formula_6 is the surface area. For a slab, we have two surfaces and they are of the same type, which is reflected by the number 2 in the denominator. To guarantee this, we need