Molecular Simulation of the Thermal and Transport Properties of Three Alkali Nitrate Salts

Abstract

Thermodynamic and transport properties for nitrate salts containing lithium, sodium, and potassium cations were computed from molecular simulations. Densities for the liquid and crystal phases calculated from simulations were within 4% of the experimental values. A nonequilibrium molecular dynamics method was used to compute viscosities and thermal conductivities. The results for the three salts were comparable to the experimental values for both viscosity and thermal conductivity. Computed heat capacities were also in reasonable agreement with experimental values. The computed melting point for NaNO3 was within 15 K of its experimental value, while for LiNO3 and KNO3, computed melting points were within 100 K of the experimental values. The results show that very small free-energy differences between the crystal and liquid phases can result in large differences in computed melting point. To estimate melting points with an accuracy of around 10 K, simulation methods and force fields must yield free energies with an accuracy of around 0.25 kcal/mol. Tests conducted on a well-studied sodium chloride model indicated negligible dependence of the computed melting point on system size or choice of integration temperature.