2 The melting T and bulk modulii vary roughly as the cohesive energies.
3 The repulsive interaction in binding in large part stems from the Pauli exclusion principle (PEP). Image that two atoms approach to each other, electron orbits will overlap. Because of PEP, if the orbit is full, some electrons have to go to higher energy orbits.
4 Van der Waals type inert gas crystals are favor close pack structure because there is no preferred interaction orientation.
5 Zero-point motion of the atom affect the accuracy of the Lennard-Jones potential model. The heavier the atom the less affection on the model.
6 Ionic crystal structures are mostly relatively empty packed. I guess the reason is the same charge interactions.
7 In ionic crystal, instead of Van der Waals potential, the total potential is sum of central field potential (short range) and coulomb potential (long range).
Definitions:
1 Cohesive energy (usually single element crystal): the energy that must be added to the crystal to separate its components into neutral free atoms at rest, at infinite separation, with the same electronic configuration. In theory, it is determined from total potential at equilibrium lattice constant.
2 Lattice energy (ionic crystals): the energy that must be added to the crystal to separate its component ions into free ions at rest at infinite separation.
3 Van der Waals-London Interaction: two electric dipole oscillators with coulomb interactions. See Kittel P-53. It is quantum interaction because the resulted attractive interaction comes from the ground state energy of two oscillators. (In classical model, ground state energy of oscillator is 0.)
4 Lennard-Jones potential: mostly applied to inert gases or molecules, it is the added up of Van der Waals-London Interaction and Repulsive Interaction.
5 Madelung constant: is the sum of all coulomb interactions on one site in an ionic crystal. Typical values: NaCl 1.75; CsCl 1.76; ZnS 1.64.
