= Gaussian chain
{c}
{title2=$\langle e^{i\mathbf k\cdot(\mathbf R_n-\mathbf R_m)}\rangle=e^{-k^2b^2|n-m|/6}$}
An ideal <Gaussian chain> is a <polymer> model whose independent segment vectors have zero mean and isotropic <Gaussian distribution>. If $\langle|\mathbf r|^2\rangle=b^2$, each Cartesian <variance> is $b^2/3$, so a displacement across $\ell$ links has density $(3/(2\pi\ell b^2))^{3/2}\exp[-3R^2/(2\ell b^2)]$ and <characteristic function> $\exp[-k^2b^2\ell/6]$. The continuous-contour version uses the same <characteristic function> for any contour separation. It is the large-scale limit of a <freely jointed chain>, while allowing unbounded Gaussian segment lengths and omitting interactions between distant parts of the chain.
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