Liquids, solution, and liquid crystals present local, but not long-range order. On one hand particles in liquids interacts much strongly than the particles in gas, and this prevents the use of the usual statistical mechanics methods to predict their structure and properties since the needed averaging process must be adapted to this situation. On the other hand, they are not as ordered as the atoms in a crystal and this prohibits the quantum mechanical computing of their electronic properties using symmetry considerations. And since several chemical reactions do not occur in gas phase and biological processes are known to take place only in aqueous environments, the understanding of the microscopic structure and behaviour of liquids is essential.In order to apprehend the importance of intermolecular forces the use of computers has become relatively common and much progress has been made in the field. In the present paper we report the results of computer simulations of different systems and the essay is arranged as follows: in Sec. I, we present a brief description of the advantages of the computer simulation and a definition of the radial distribution function (RDF). Section II explains how water behaves in a liquid phase. Section III will focus on the ionic hydration and on the temperature influence; whereas section IV will look into the non ionic hydration of Argon, tetrafluoromethane and nanopore. Finally, in Sec. V, we draw the main conclusion from our work.
[...] This is a consequence of the average expected orientation of oxygen and hydrogen around the ionic species. Figure 5. The SPC water Model As the natural configuration of a water molecule near Na+ has it's oxygen as near as possible to the positive ion and it's hydrogen as far away as achievable Figure this naturally leads to an average distance of 0.58 Å (Figure 5). For the natural configuration has one hydrogen as near as possible to the negative ion and the oxygen as far away as doable (Figure corresponding to a radial distance of 1 Å. [...]
[...] This subject will be briefly described later in the text - Perfluoroalkanes hydration Computer simulations aren't limited anymore to model small systems, interactions with bigger molecules such as perfluoroalkanes can be easily considered. Only 1 tetrafluoromethane (CF4) molecule surrounded by 500 molecules of water was simulated with a Monte Carlo method, thermodynamic variables were set to reproduce liquid water at room temperature. Figure 8. Radial Distribution Function of CF4 The RDFs of the molecule, shown in Figure present many matching features with the Argon RDFs. [...]
[...] After the simulation process, thermodynamics and structural properties of the system can be calculated. The radial distribution function (RDF) is the most informative feature of the molecular structure and will use be as the backbone of our work. The RDF, then, is the probability of finding an atom of species j at a radial distance of atom i related to the probability of finding this pair of atoms in a totally randomly distributed system with similar density. A schematic illustration of the calculation of gij(r) is pictured in Figure 1 who shows a bi-dimensional cut of a cluster of atoms. [...]
[...] MC and MD simulation methods have become a promising tool to study fluids even under extreme conditions and can potentially provide the much needed insight into the physics of fluids under extreme conditions and hence reengineer existing geochemical equations of state or even find new approaches to their formulations Ionic hydration in infinitely dilute solutions Only 1 solute or Cl- ion) surrounded by 200 molecules of water was simulated with a MC method, thermodynamic variables were set to reproduce liquid water at room temperature. [...]
[...] The simulation of ionic solutions under different state and concentration is the first step to more complicated study such as ionic liquids (organic salts, liquid at room temperature, with potential applications in cleaner reaction systems and separation processes) or proteins. Studies of concentrated solutions or complex molecules were usually carried out on very small systems not acceptable for a representative simulation of the molecular scale. Fortunately the situation has changed with the increase of the computational capacity and remains nowadays an active field of research. [...]
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