We estimated the accuracy of the theoretical predictions for the structure of liquid n-butanol resulting from the model calculations implemented by various force fields: GROMOS96-54a7, CHARMM27, OPLS-AA, AMBER03, and TraPPE-UA. For this purpose we performed extensive molecular dynamic simulations of model alcohol and measurements of small- and wide-angle X-ray scattering of liquid n-butanol. Utilizing the Complemented system approach method developed for the calculation of X-ray scattering from simulation data scattering intensities of model n-butanol resulting from simulations were calculated and compared to the experimental scattering data. The simulation results show that all the tested models reproduce the basic characteristics of the experimental scattering curves of n-butanol. However, minor qualitative to considerable quantitative discrepancies in the shape of the scattering functions referring to different force fields are still observed and assigned to different model parametrizations. Simulation results were presented and discussed also via the radial and spatial distribution functions and through the H-bonding data.
COBISS.SI-ID: 1537336771
We proposed a simple model of associating hard spheres with highly nontrivial fluid-solid phase behavior and studied it using the thermodynamic perturbation theory for central force associating potentials and Monte Carlo simulation. The phase diagram has the fluid branch of the fluid-solid coexistence curve located at a temperatures lower than those of the solid branch. This unusual behavior is related to the strong dependence of the system excluded volume on the temperature, which for the model at hand decreases with increasing temperature. This effect can be also seen for a wide family of fluid models with an effective interaction that combines short range attraction and repulsion at a larger distance.
COBISS.SI-ID: 1537347523
A simple three-dimensional Mercedes-Benz model of water was used to study its phase behavior and thermodynamic properties. Water molecules were presented as soft spheres with four directions in which hydrogen bonds can be formed. For pure water, we explored the temperature dependence of the density, heat capacity, thermal expansion coefficient, and isothermal compressibility. We found out that these calculated values are in good agreement with Monte Carlo simulations data and show the same temperature dependence as observed in real water. The model exhibits two critical points for liquid-vapor transition and transition between low-density and high-density fluid. Coexistence lines therefore divide the phase space in three parts: vapor, high-density liquid, and low-density liquid regions.
COBISS.SI-ID: 1537232067