Quantum well states density functional theory

Over the past decade, Kohn-Sham density functional theory (DFT) has evolved into what is now one of the major approaches in quantum chemistry.1-20 It is routinely applied to various problems concerning, among other matters, chemical structure and reactivity in such diverse fields as organic, organometallic, and inorganic chemistry, covering the gas and condensed phases as well as the solid state. What is it that makes Kohn-Sham DFT so attractive Certainly, an important reason is that it represents a first-principles... 

Since it s inception in 1967, the Advances in Quantum Chemistry series has attempted to present various aspects of atomic, molecular, and solid state theory at the cutting edge. The contributions have taken various forms, from longer review articles to conference proceedings, and most of them have been well received. In this issue, we continue in this trend, and address some of the fundamental issues in density functional theory (DFT). DFT is extremely popular these days in its applied form It is almost impossible to read an experimental article where explanation of the results does not involve a DFT calculation using one or another commercial program and implementing one or another parameterized potential scheme. However, the success of applied DFT seems to be that it works, rather than the result of critical analysis of the fundamentals of the theory. However, the community also needs to explore the limits of the theory itself, and it is with this that the first four contributions in this issue concern themselves. 

As indicated before, the ab initio electronic-structure theory of solid-state materials has largely profited from density-functional theory (DFT), and the performance of DFT has turned out well even when the one of its molecular quantum-chemical competitors - Hartree-Fock theory - has been weakest, namely for metallic materials. For these, and also for covalent materials, DFT is a very reasonable choice. On the other hand, ionic compounds (with both metals and nonmetals present) are often discussed using only the ionic model, on which most of Section 1.2 was based, and the quantum-mechanical approach is not considered at all, at least in introductory textbooks. Nonetheless, let us see, as a first instructive example, how a t5q)ical ionic material can be described and understood by the ionic and the quantum-chemical (DFT and HF) approaches, and let us also analyze the strengths and weaknesses. 

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