Bulk structural information from density functionals for patchy particles

We investigate bulk structural properties of tetravalent associating particles within the framework of classical density functional theory, building upon Wertheim's thermodynamic perturbation theory. To this end, we calculate density profiles within an effective test-particle geometry and compare to radial distribution functions obtained from computer simulations. We demonstrate that a modified version of the functional proposed by Yu and Wu [J. Chem. Phys. 116, 7094 (2002)] based on fundamental measure theory for hard spheres produces accurate results, although the functional does not satisfy the exactly known low-density limit. In addition, at low temperatures where particles start to form an amorphous tetrahedral network, quantitative differences between simulations and theory emerge due to the absence of geometrical information regarding the patch arrangement in the latter. Indeed, here we find that the theory fits better to simulations of the floating-bond model [E. Zaccarelli et al., J. Chem. Phys. 127, 174501 (2007)], which exhibits a weaker tetrahedral order due to more flexible bonds between particles. We also demonstrate that another common density functional approach by Segura et al. [Mol. Phys. 90, 759 (1997)] fails to capture fundamental structural properties.