International Journal of Nanoscience Volume 7, Nos. 4 & 5, Pages 245–253, 2008 BEHAVIOR OF THE CONFINED HARD-SPHERE FLUID WITHIN NANOSLITS: A FUNDAMENTAL-MEASURE DENSITY-FUNCTIONAL THEORY STUDY MOHAMMAD KAMALVAND (*) and TAHMINEH (EZZAT) KESHAVARZI Department of Chemistry Isfahan University of Technology Isfahan, Iran, 841568311 G.ALI MANSOORI Departments of Bioengineering Chemical Engineering and Physics University of Illinois at Chicago Chicago, IL 60607-7052, USA A property of central interest for theoretical study of nanoconfined fluids is the density distribu- tion of molecules. The density profile of the hard-sphere fluids confined within nanoslit pores is a key quantity for understanding the configurational behavior of confined real molecules. In this report, we produce the density profile of the hard-sphere fluid confined within nanoslit pores using the fundamental-measure density-functional theory (FM-DFT). FM-DFT is a powerful approach to studying the structure and the phase behavior of nanoconfined fluids. We report the computational procedure and the calculated data for nanoslits with different widths and for a wide range of hard-sphere fluid densities. The high accuracy of the resulting density profiles and optimum grid-size values in numerical integration are verified. The data reveal a number of interesting features of hard spheres in nanoslits, which are different from the bulk hard-sphere systems. These data are also useful for a variety of purposes, including obtaining the shear stress, thermal conductivity, adsorption, solvation forces, free volume and prediction of phase transitions. Keywords : Density-functional theory (DFT); density profile; fundamental-measure DFT (FM- DFT); hard-sphere equation of state; nanoconfined fluid; nanoslit; nanoscience; nanotechnology; phase transition. 1. Introduction Modern condensed matter theory relies heavily on the knowledge and understanding of the structural and thermodynamic properties of model systems. Among these, the hard-sphere model has been stud- ied extensively and plays an important role in the variational and perturbation theories of condensed matter and phase transitions. 1–3 This is analogous 245 (*) Corresponding Author; Present address: Department of Chemistry, Yazd University, Yazd, Iran Authors email addresses: M. Kamalvand: kamalvand@yazd.ac.ir T. Keshavarzi: keshavrz@cc.iut.ac.ir G.A. Mansoori: mansoori@uic.edu https://doi.org/10.1142/S0219581X08005365