抄録
In the recent article, we have calculated the long-range correlation length, ξ, for monatomic fluids near the critical region using our theoretical model for the direct correlation function, DCF. In this model the core of DCF has assumed modified Percus–Yevice function for the DCF of hard sphere and its tail has been considered as a Mayer-f function type via an effective pair potential. In this article, we have predicted the behaviour of low-angle structure of factor, S(k). Since, the model is able to predict the divergence behaviour of S(0) at this region which is related to critical fluctuation phenomena, we may obtain ξ via that. Also, since the DCF is always short-range at any thermodynamic state, we may obtain the coefficients of small-k expansion of c(k), Fourier transform of DCF, which are related to the intermolecular interactions at the critical region. In all cases, the coefficient of k2 term in the expansion of c(k), c2, which is related to correlation length, is negative because S(k) shows Ornestine–Zernike behaviour at small-k. We have obtained the range of k in which c2 may be calculated from the expansion of c(k). This range depends on the thermodynamic states and decreases far away from the critical point. The correlation length shows divergence behaviour when the critical point approaches. We have shown, for supercritical of Krypton, the variation of correlation length with reduced temperature (T−Tc)⁄Tc has a power–law relation with a critical exponent equal to 0.89. Finally the relation of the correlation length with effective intermolecular parameters has been investigated.
