We study the structural and thermodynamic properties of three discrete potential fluids: the square well (SW), the square well-barrier (SWB), and the square well-barrier-well (SWBW) fluids by means of the Ornstein-Zernike (OZ) integral equation and the HMSA (hybrid mean spherical approximation) closure relation. The radial distribution functions, structure factors, and pressure of the systems are calculated as a function of the strength of the attractive and repulsive parts of the potential in an extended range of densities, mainly covering the range 0.1 ρ * 0.9. We find that far away from the liquid-vapour coexistence region the HMSA theory is an accurate approach that compares well with Monte Carlo simulations. We also find that when the attractive parts of the potential dominate over the repulsive part the structure factor at low q values shows a considerable increase, which suggests the formation of large-scale domains that locally exhibit fluid-like structure.

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The finite temperature spin and orbital magnetism of N≤ 10 Fe(N) linear chains is theoretically studied in the framework of a spin fluctuation theory based on a realistic d-band model Hamiltonian, which includes the spin-orbit coupling interaction in a non-perturbative way. Spin and orbital magnetic moments are calculated as a function of the temperature by using an exchange Monte Carlo method that takes into account in a full way the short-range magnetic order. The finite temperature anisotropy effects on the spin and orbital cluster moment values are analysed by considering magnetization directions perpendicular to and along the chain axis. The temperature dependence of the orbital cluster moment follows a general trend similar to that of the spin one and shows clear anisotropy effects at low and intermediate temperatures, before total thermal disorder appears. Interesting anisotropy effects driven by thermal spin fluctuations are also observed for the spin results in most of the systems.

We report the improvement of five argon force fields by scaling Lennard-Jones energy (ǫ) and distance (σ) parameters to reproduce liquid-vapor phase diagram and surface tension simultaneously, with molecular dynamics. Original force fields reproduce only liquid-vapor phase diagram among other properties except surface tension. Results showed that all force fields converge in a nearby region in the ǫ-σ phase space, which is different from the original values. This study gives the intervals where the numerical values of ǫ and σ reproduce both properties mentioned above.