Naively, one might expect that at least approximate solutions of the many-particle problem in the form of the eigenvalues and eigenfunctions of the Hamiltonian, as introduced in the last chapter, would be an unambigous condition for proceeding further. Indeed, there are many experimental data, ranging from ground-state properties to response functions, which can be directly related to this information. But, apart from the problem that there is no hope of solving the many-particle problem exactly, there would also be no chance of dealing with the tremendous wealth of mostly superflous information. Fortunately, this is not the only way to proceed. Concerning macroscopic properties as measured experimentally, most of the microscopic information is redundant.
KeywordsSlater Determinant Transition Matrix Element Bloch Function Wannier Function Valence Charge Density
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