Hybrid covalent energy defined

For homopolar semiconductors, we see from Eq. (4-17) that it is twice the covalent energy -in contrast to the hybrid covalent energy of Eq. (3-6)- defined by... 

For polar covalent solids, sp hybrids of the form of Eq. (3-1) can be constructed on each of the atom types present and oriented in the directions of its nearest neighbors. The hybrid energies will be different we call the lesser energy and the greater energy i-, and, in direct analogy with Eq. (1-32), define a hybrid polar energy proportional to their difference ... 

Consider hexagonal boron nitride, shown in Fig. 3-10. Define a hybrid covalent and hybrid polar energy for this structure, in analogy with the corresponding definitions for tetrahedral solids in Eqs. (3-4) and (3-6). Compare the polarity obtained from these values with that of tetrahedral BN, listed in Table 7-2. Take d = 1.42 A as in graphite. Notice that many values arc modified by having sp hybrids rather than sp hybrids. 

Bond orbitals are constructed from sp hybrids for the simple covalent tetrahedral structure energies are written in terms of a covalent energy V2 and a polar energy V3. There are matrix elements between bond orbitals that broaden the electron levels into bands. In a preliminary study of the bands for perfeet crystals, the energies for all bands at k = 0 are written in terms of matrix elements from the Solid State Table. For calculation of other properties, a Bond Orbital Approximation eliminates the need to find the bands themselves and permits the description of bonds in imperfect and noncrystalline solids. Frrors in the Bond Orbital Approximation can be corrected by using perturbation theory to construet extended bond orbitals. Two major trends in covalent bonds over the periodic table, polarity and metallicity, are both defined in terms of parameters from the Solid State Table. This representation of the electronic structure extends to covalent planar and filamentary structures. 

We must now make a sharp distinction between the concepts we are using and the parameters of the theory. The V l and defined in the preceding paragraphs for the hybrid bond are the direct counterparts of covalent and polar energies... 

---