Theoretical study of the solvation of nitrogen. Two different approaches

Abstract

Abstract\ud Two different approaches were used for a theoretical study of the solvation of N2, with HF, H2O, NH3, CH4 as solvents. In the first approach, the contour maps of orientationally optimized interaction energy between N2 and one solvent molecule were computed by fast semiempirical methods (Extended Hückel and CNDO/2) in order to find a reliable but not too expensive calculation method for solvation models. In the case of the N2-H2O system, an ab initio map was also evaluated for comparison. The second approach is based on the building up of clusters with one molecule of N2 surrounded by a number (2 to 8) of solvent molecules and finding the structure of such clusters by energy minimization. From the structures obtained it results that they are determined mainly by steric factors, so that clusters optimized by means of different methods are similar, despite the remarkable differences in the maps

The behaviour of water confined in zeolites: molecular dynamics simulations versus experiment

“…In order to perform MD simulations of complex systems such as zeolites (where in a crystalline solid exchangeable cations and guest mobile molecules are hosted) suitable potentials are required to model the crystalline framework as well as the guest-guest and the framework-guest interactions. In the first attempt to simulate a hydrated zeolite (natrolite) [50], we held the framework fixed, a choice that is still often adopted, mainly in order to save computer time. However, we met an immediate criticism on this point, and from then on we developed and have always adopted flexible zeolite framework models to include lattice deformations and vibrations in the simulated system.…”

An intermoleeular potential function for the N2−H2O system fromab initioMO calculations

“…The ab initio map reported in [10] was calculated to be compared with analogous semiempirical maps and must be regarded as an essentially qualitative one, showing the principal features of a real potential. For instance, the local minimum which does not lie on any symmetry element could persist in maps obtained by more sophisticated calculations and the problems which will arise in the fitting will be similar to those discussed in this paper.…”

“…In the course of our research on the solvent effect on the dediazoniation reaction [7,8] both the problems of the interaction of nitrogen with different solvents and the reliability of different computational techniques were investigated in detail [9,10]. In preparation for extending the study of the solvation of nitrogen in water to statistical methods we report herein details and characterization studies of an analytical potential function for the system N2-H20 fitted to ab initio LCAO-MO-SCF calculations.…”

“…The latter ab initio calculations were performed with a gaussian minimal basis set (7/3) [11] and the IBMOL--6 program of Clementi et al [12] was employed. The details of the ab initio calculations are available in [10].…”

Molecular Dynamics Study on the Adsorption Selectivity for Negative Elements in Aluminosilicates

“…For example, Demontis and co-workers reported the positions and vibrations of water molecules in the cages of natrolite [20,21], the atomic coordinates and the crystal symmetry of dehydrated natrolite [22] and Linde zeolite 4A [23], the diffusive motion of methane in silicate [24] and the structural changes of silicate at different temper atures [25]. Cohen de Lara and co-workers also performed an MD study of methane adsorbed in zeolite-A [26] based on their potential-energy calcula tion [27].…”