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31 32 1 Classical Approaches Tab. 2 Volume increments according to Biltz [33] including basis, regular and uncertain values. 4 Volume Increments Tab. 2 33 34 1 Classical Approaches In practice, the derivation of these increments was performed in a similar way to Goldschmidt’s derivation of ionic radii, namely starting from the alkali halides and thereby deriving basis values, then extending it to other materials. At least two interesting observations can be made from the latter table which, although very dated (1934), is still in use in many solid-state chemical laboratories.

529 Å). 5 Hartree. 211 eV; this systems is widely used in the quantum-chemistry community. 606 eV, and the new unit is called one Rydberg. Thus, one Hartree equals two Rydbergs, and there are two types of atomic unit. 2) According to a world-famous theoretical chemist, there are several dozens of quantumchemical approaches available, and each of them is superior to all the others. 1 Schrödinger’s Equation When it comes to the actual construction of the wave function Ψ for many electrons (therefore called a many-electron or many-body wave function), experience has shown that additional information, touching upon the amount of electron–electron interaction within the system, helps to come up with a good starting point.

For the sake of the empirical concept derived here, we will suppress this counterargument for the moment. In addition, there is hardly anything more appealing than a nicely working concept that is fundamentally flawed (I am, of course, joking here). One great advantage of the modern bond-valence concept [39], developed by Donnay, Allmann, Brown, Altermatt and many others [40], is that it does not rely on any kind of distinction whatsoever between ionic or covalent bonding; both are mapped into the same formalism, and the cation/anion terms simply stand for the less/more electronegative bonding partners, that is, Lewis acids and bases.