Concluding remarks on different theoretical approaches

In this book, the main focus is on the application of quantum-mechanical methods to elucidate the geometric and electronic structures of minerals, so that detailed discussion of the relative merits of the different approaches is not appropriate. Nonetheless, it is important for the reader to appreciate some of the major controversies that have arisen between theoreticians in the field. 

Another area of controversy has been the choice of Hartree-Fock (or Hartree-Fock plus Cl) methods as against density-functional methods. For example, Goodgame and Goddard (1982, 1985), Bernholc and Holz-warth (1983), and Delley et al. (1983) have debated the use of Hartree-Fock versus density-functional theory to describe the very complex and 

It is important to keep in mind that eaeh such piece of software is the product of hundreds (or more) person-years of work and should be treated as a valuable resource. Even the most user-friendly programs can be unintentionally misused to produce erroneous or misleading results, vindicating the ancient computer science axiom garbage in = garbage out. On 

A functional is an expression whose value depends on the values of a function [in this case p(r)] rather than on a set of independent variables. 

In principle, the Kohn-Sham orbitals obtained as solutions to Eq. (3.39) are for noninteracting particles, not the real electrons, but in practice this difference is often ignored. 

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