Cohesive noble gases

This formula has been refined [77] for the calculation of the molar cohesive energy of noble gas crystals into ... 

Table 5.4 Details for the calculation of solid-state noble gas cohesive energies.

In order to describe the cohesion in the same terms as was done for metals and noble gas crystals, electron density is proposed to accumulate in the vacant interstitial octahedral sites and the remaining tetrahedral sites. This distribution is shown for two CC4 tetrahedral units in Figure 5.17. The central carbon in the outlined tetrahedron is surrounded by an octahedron (in stippled outline) of interstitials defined by the set of vacant tetrahedral sites. 

The advanced methods allow one to calculate equilibrium lattice constants and cohesive energies of the noble gas crystals. 

Harl, J. and Kresse, G. (2008) Cohesive energie curves for noble gas solids calculated by adiabatic connection fluctuation-dissipation theory. Phys. Rev. B, 77, 045135-1-045136-8. 

Use of this potential can then provide a quantitative measure of cohesion in these solids. One measure of the strength of these potentials is the vibrational frequency that would correspond to a harmonic oscillator potential with the same curvature at the minimum this is indicative of the stiffness of the bond between atoms. In Table 1.1 we present the frequencies corresponding to the Lennard-Jones potentials of the common noble gas elements (see following discussion and Table 1.2 for the relation between this frequency and the Lennard-Jones potential parameters). For comparison, the vibrational frequency of the H2 molecule, the simplest type of covalent bond between two atoms, is about 500 meV, more than two orders of magnitude larger the Lennard-Jones potentials for the noble gases correspond to very soft bonds indeed ... 

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