Attractive force long/short range

Interpreting bulk properties qualitatively on the basis of microscopic properties requires only consideration of the long-range attractive forces and short-range repulsive forces between molecules it is not necessary to take into account the details of molecular shapes. We have already shown one kind of potential that describes these intermolecular forces, the Lennard-Jones 6-12 potential used in Section 9.7 to obtain corrections to the ideal gas law. In Section 10.2, we discuss a variety of intermolecular forces, most of which are derived from electrostatic (Coulomb) interactions, but which are expressed as a hierarchy of approximations to exact electrostatic calculations for these complex systems. 

Van der Waals forces are very complex and manifest themselves even at distances at which it is unreasonable to assume that orbital interactions can occur. An explanation due to London in terms of the mutual attraction of induced dipoles (dispersion forces) accounts for the long-range behavior. The unoccupied-occupied orbital interactions will be the dominant component of van der Waals forces at short range. See Kauzmann, W., Quantum Chemistry, Academic, New York, 1957, Chapter 13, for a discussion of dispersion forces. 

The basic principle of self-assembly is based on the simultaneous coexistence of two parallel forces [85, 86], long-range repulsive forces and short-range attractive interactions. 

Fig. 8.11. (a) Structural force per unit area in a heterophase paranematic (thick lines) and nematic system with molten boundary layers (thin lines). Solid lines correspond to the force in the nematic phase and dashed lines to the force in the isotropic phase. For the thicknesses above the corresponding verticals the isotropic (paranematic) or nematic phase is stable, respectively. The force is short-range and attractive, (b) Structural presure in the hybrid nematic system in a biaxial structure (solid line) and bent-director structure (dashed line). In both cases the interaction is long-range and repulsive. 

The potential model describes the variation of energy of the system as a function of the atomic coordinate. This energy is derived from the long-range electrostatic forces and short-range attractive and repulsive forces, or the coulombic contribution, whereas the short-range interactions are described using simple parameterized functions. A potential model that accurately describes the lattice properties is essential if quantitative resnlts are to be obtained. This is particularly important for surfaces for which it is necessary to describe the interaction at distances possibly far removed from those found in the bulk lattice (Allan et al. 1993). 

The above potential is referred to as a Lennard-Jones or 6-12 potential and is summed over all nonbonded pairs of atoms ij. The first positive term is the short range repulsion and the second negative term is the long range attraction. The parameters of the interaction are Aj and B... The convenient analytical form of the 6-12 potential means that it is often used, although an exponential repulsion term is usually considered to be a more accurate representation of the repulsive forces (as used in MM-t). 

Debye-Huckel theory assumes complete dissociation of electrolytes into solvated ions, and attributes ionic atmosphere formation to long-range physical forces of electrostatic attraction. The theory is adequate for describing the behaviour of strong 1 1 electrolytes in dilute aqueous solution but breaks down at higher concentrations. This is due to a chemical effect, namely that short-range electrostatic attraction occurs... 

Ionically bonded crystals contain both long-range and short-range bonding forces because like ions repel each other, while unlike ones attract. 

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