1. Chapter 32.;Ashcroft,1976
2. Chapter 8.;Kittel,1987
3. A quantum mechanical calculation of the elastic constants of monovalent metals
4. Chapter 5.;Ziman,1960
5. However, in semiconductors and insulators, electrons at isolated defects can sometimes remain in excited-state configurations for times long in comparison with typical time scales for ionic motion, invalidating a ground-state description. This issue will be discussed in Section 12.