Metallic cohesion

The trend in the f-pressure is almost parabolic with band filling and this is typical for a transition metal (with d replaced by f). The physical basis was given by the Friedel who assumed that a rectangular density of states was being filled monotonically and thus was able to reproduce the parabolic trend in transition metal cohesive energies analytically. Pettifor has shown that the pressure formula can similarly be integrated analytically. 

This concept of metallic cohesion as arising from embedding ions in a gas of free electrons suggests that the binding energy of a collection of atoms with position vectors Rf may be approximated in the form of an embedded atom potential, namely... 

The nature of these two phases helps to throw light on the metal-nonmetal transition. For example there has been much speculation that hydrogen molecules at sufficiently high pressure, such as those occurring on the planet Jupiter, might undergo a transition to un alkali metal The fundamental transition is one of a dramatic change of the van der Waals interactions of H, molecules into metallic cohesion. ... 

The precise nature of the electronic interactions between centers must obviously change dramatically at the NM-M transition, e.g., from van der Waals type interaction to metallic cohesion (112). These gross changes in electronic properties at the transition are sufficient to noticeably influence the thermodynamic features of the system (86,87). The conditions therefore appear highly conducive for a thermodynamic phase transition to accompany the electronic transition at the critical density. In fact, the transition to the metallic state in metal-ammonia solutions is accompanied by a decrease in both enthalpy and entropy (146, 149), and it has been argued convincingly (124, 125) that the phase separation in supercritical alkali metals and metal solutions is... 

Ever since this breakthrough, C60 has been intensively studied and has shown its rich bonding characteristics in various environments, from van der Waals cohesion to ionic and metallic cohesions, and even to the extent of covalent bonding, together also with its rich electronic properties including high transition-temperature (Tc) superconductivity in alkali-doped C60 fullerides. This article reviews the first-principles quantum-mechanical studies of these electronic and bonding properties of C60. 

The atomic adsorption on metals is not caused by van-der Waals forces, but depends on forces similar to those postulated by Slater for explaining metallic cohesion... 

Scheme 3-5. Pictorial representation of the structural changes caused by the addition of electrons (a) intramolecular loss of metal cohesion upon a change in the number of CVE in the [Os6(CO)i8]-[Os6(CO)i8] pair of compounds, [187, 188] (b) fragmentation of [Pti2(CO)24] into two [Pt (CO)i2] ions.

Fig. 2. Calculated properties of the 3d and 4d transition metals-cohesive energy, lattice constant, and bulk modulus- compared with experiment (crosses). This represents a milestone in the development of the methods to calculate with sufficient accuracy to find these quantities. (From refs. 25 and 123, figure courtesy of V. MoruzzO... 

Although not always bringing great advances, several other model potentials were proposed [47,48,49], Also, many different methods for adjusting the parameters were suggested [50], The main application of these model potentials was to the theory of metallic cohesion [51,52,53,54,55],... 

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