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6.5 Particles and Fields

In many cases the interparticle potential may be safely neglected beyond
a few particle diameters. Defining a cutoff distance ,
we may estimate the importance of the neglected
``tail'' of a potential by

If the decay of is slow, this integral may be non-negligible.
For example, the interaction between charged particles
decays only as , and any cutoff will introduce a considerable
error. Another instance is astrophysics, where the gravitational potential
reaches too far to permit a simple cutoff.

For ionic systems that are globally neutral the **Ewald summation**
method known from solid state physics may be invoked. In the case of
hot plasmas or gravitating systems the **Particle-Mesh**
methods are appropriate.

**Subsections**

* Franz J. Vesely Oct 2005*

See also: "Computational Physics - An Introduction," Kluwer-Plenum 2001