Cohesive energy

Here’s a site that lists cohesive energies.

Copper, for example, is listed as having a cohesive energy of 336 kJ / mol, which also translates into 3.49 eV / atom.

In the solid state, copper atoms interact with other atoms sitting next to them in a fairly complicated way. If we ignore such complications arising from multi-atom interactions, we may think in terms of pairwise (copper-copper) bonds that extend only to nearest neighbours.

Copper has a face-centred cubic structure in which each atom has 12 nearest neighbours. Thus, the cohesive energy of 3.49 eV / atom is the energy needed to break six (= 12 / 2) bonds. [Why six, instead of 12?]

In this picture, then, the energy of each copper-copper nearest neighbor bond is -0.58 eV.

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