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Lifshitz Theory of Van der Waals Force
In condensed matter physics and physical chemistry, the Lifshitz theory of Van der Waals forces, sometimes called the macroscopic theory of Van der Waals forces, is a method proposed by Evgeny Mikhailovich Lifshitz in 1954 for treating Van der Waals forces between bodies which does not assume pairwise additivity of the individual intermolecular forces; that is to say, the theory takes into account the influence of neighboring molecules on the interaction between every pair of molecules located in the two bodies, rather than treating each pair independently.
== Need for a Non-Pairwise Additive Theory ==
The Van der Waals force between two molecules, in this context, is the sum of the attractive or repulsive forces between them; these forces are primarily electrostatic in nature, and in their simplest form might consist of a force between two charges, two dipoles, or between a charge and a dipole. Thus, the strength of the force may often depend on the net charge, electric dipole moment, or the electric polarizability () (see for example London force) of the molecules, with highly polarizable molecules contributing to stronger forces, and so on.
The total force between two bodies, each consisting of many molecules in the Van der Waals theory is simply the sum of the intermolecular Van der Waals forces, where pairwise additivity is assumed. That is to say, the forces are summed as though each pair of molecules interacts completely independently of their surroundings (See Van der Waals forces between Macroscopic Objects for an example of such a treatment). This assumption is usually correct for gasses, but presents a problem for many condensed materials, as it is known that the molecular interactions may depend strongly on their environment and neighbors. For example, in a conductor, a point-like charge might be screened by the electrons in the conductance band, and the polarizability of a condensed material may be vastly different from that of an individual molecule. In order to correctly predict the Van der Waals forces of condensed materials, a theory that takes into account their total electrostatic response is needed.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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