Nitrogen applied computational methods

Ab initio calculations were carried out for all the low-lying non-Rydberg states of the systems N2, 02, NO, Of, and NO+. In N2, for example, there are 102 molecular states that result from nitrogen atoms in the lowest 4S, 2D, and 2P states. These states were all uniformly described using VCI wave functions constructed as described in Section II. Minimum basis, double-f basis and double-f-plus-polarization basis sets were employed for these studies. For the minimum basis-set calculations, which were always carried out first, the VCI wave functions represent full Cl projections with the constraint that the K shells were kept frozen for all states. However, no constraint on the 2og and 2ou orbitals was made since a Cl among these orbitals is necessary to ensure proper description of the hole states in these molecules, such as C3n of N2. The calculations all have the property of asymptotically connecting with the correct atomic states. This computational method has previously been applied, with reliable results, to both closed- and open-shell systems.6 9 11... 

However, it should be noted, that methods like the BJH, which are based on the macroscopic Kelvin equation, provide not a reliable basis for the calculation of pore widths < 5 nm [11,16,17]. Compared with new methods that rely on microscopic descriptions like the density functional theory (DFT) and Monte Carlo computer simulation (MC), the macroscopic thermodynamic methods underestimate the calculated pore diameter by ca. 1 nm [11,17]. In addition, it is argued that in case of nitrogen as adsorptive the BJH and related methods based on the Kelvin equation cannot be applied below a relative pressure p/po = 0.42 because this relative pressure is considered as the limit of the thermodynamic stability of liquid nitrogen. Hence, pore sizes obtained by application of the BJH method should be regarded as apparent rather than real pore sizes [7]. 

Haapaniemi et al have investigated by NMR spectroscopy and theoretical methods a set of 15 compounds scheduled in the Chemical Weapon Convention (sulphur mustards, nitrogen mustards, and lewisites) in order to compute and predict reference spectra. As a part of these investigations, the authors calculated chemical shifts and H,H couplings applying the B3LYP functional with PCS-0, PCJ-0, and PCS-2 basis sets. 

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