 Static structure factor

The static structure factor is the spatial Fourier transform of an equal-time two-point correlation function, with normalization and any disconnected contribution specified. It describes how spatial fluctuations contribute at each transferred wavevector.

If the dynamic structure factor is defined using the same correlation and the Fourier factor $e^{i\omega t}$, thenThe integral sets the time separation to zero. Evaluating the dynamic spectrum only at zero frequency instead selects a different quantity and generally does not produce the equal-time structure factor. A scattering experiment integrated over energy transfer can measure the static quantity after the relevant kinematic and detector corrections. A narrow peak near an ordering wavevector indicates long spatial correlations; it is not by itself a direct measurement of their relaxation time.