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Cell lists : ウィキペディア英語版
Cell lists
Cell lists (also sometimes referred to as cell linked-lists) are a tool for finding all atom pairs within a given cut-off distance of each other in molecular dynamics simulations. These pairs are needed to compute the short-range non-bonded interactions in a system, such as Van der Waals forces or the short-range part of the electrostatic interaction when using Ewald summation.
==Algorithm==

Cell lists work by subdividing the simulation domain into cells with an edge length greater than or equal to the cut-off radius of the interaction to be computed. The particles are sorted into these cells and the interactions are computed between particles in the same or neighbouring cells.
In its most basic form, the non-bonded interactions for a cut-off distance r_c are computed as follows:
:for all neighbouring cell pairs (C_\alpha, C_\beta) do
::for all p_\alpha \in C_\alpha do
:::for all p_\beta \in C_\beta do
::::r^2 = \| \mathbf x() - \mathbf x() \|_2^2
::::if r^2 \le r_c^2 then
:::::Compute the interaction between p_\alpha and p_\beta.
::::end if
:::end for
::end for
:end for
Since the cell length is at least r_c in all dimensions, no particles within r_c of each other can be missed.
Given a simulation with N particles with a homogeneous particle density, the number of cells m is proportional to N and inversely proportional to the cut-off radius (i.e. if N increases, so does the number of cells). The average number of particles per cell \overline = N/m therefore does not depend on the total number of particles. The cost of interacting two cells is in \mathcal O(\overline^2). The number of cell pairs is proportional to the number of cells which is again proportional to the number of particles N. The total cost of finding all pairwise distances within a given cut-off is in \mathcal O(Nc) \in \mathcal O(N), which is significantly better than computing the \mathcal O(N^2) pairwise distances naively.

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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