Assessment of three-dimensional distribution functions and triplet distribution functions for hard spheres calculated using a three-dimensional Ornstein-Zernike equation with hypernetted-chain closure

We calculated three-dimensional distribution functions around a contact dimer composed of hard spheres immersed in a fluid composed of same-sized hard spheres calculated using a three-dimensional Ornstein-Zernike equation with hypernetted-chain closure (3D-HNC-OZ theory). The results of the 3D-HNC-OZ theory were compared with those calculated using Monte Carlo simulations. Even though the packing fraction of solvent was high, such as in ambient water, the 3D-HNC-OZ theory gave semiquantitatively reasonable results. This means that the triplet distribution function was also calculated reasonably well, although the triplet distribution functions are not explicitly included in the equations of the 3D-HNC-OZ theory. However, the accuracy depended on the configuration of the solute. Our results are discussed in a biological context, such as molecular recognition and the stability of folded proteins.