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The pair distribution function (PDF) describes the distribution of distances between pairs of particles contained within a given volume. Mathematically, if ''a'' and ''b'' are two particles in a fluid, the PDF of ''b'' with respect to ''a'', denoted by is the probability of finding the particle ''b'' at the distance from ''a'', with ''a'' taken as the origin of coordinates. == Overview == The pair distribution function is used to describe the distribution of objects within a medium (for example, oranges in a crate or nitrogen molecules in a gas cylinder). If the medium is homogeneous (i.e. every spatial location has identical properties), then there is an equal probability density for finding an object at any position : :, where is the volume of the container. On the other hand, the likelihood of finding ''pairs of objects'' at given positions (i.e. the two-body probability density) is not uniform. For example, pairs of hard balls must be separated by at least the diameter of a ball. The pair distribution function is obtained by scaling the two-body probability density function by the total number of objects and the size of the container: :. In the common case where the number of objects in the container is large, this simplifies to give: :. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「pair distribution function」の詳細全文を読む スポンサード リンク
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