Pure systems, parameterization

Because the electrostatic energy terms for an uncharged pure system (such as a bulk structure) is zero, the energy contribution of COMB for such a system is from the short-range interactions [eqn (7.18)] and the formalism is reduced to the Tersoff type of potential. This case is straightforward for the parameterization of the COMB potential, which only fits parameters in the pairwise term and bond-order terms, as shown in Table 7.2. The van der Waals interaction will be considered for hydrocarbon systems. 

Lastly, the COMB poetical is fit to the binary system with multiple phases. Similar to the parameterization process for a pure system, the potential starts with fitting the pairwise terms to the phase orders and charge of a variety of binary systems, which is followed by fitting the parameters in many-body terms to the properties of the binary system. The parameters involved in the binary system are listed in Table 7.4. 

Vapour pressures for a number of atmospherically relevant condensed systems have been measured with mass spectrometry. These systems include hydrates of HC1, HjS04 and HNO, supercooled liquids and pure water-ice, as well as the interactions of HC1 vapour with die solids, ice and NAT [23,47,50-55]. Vapour pressure measurements over HNOj/HjO hydrates have also been made using infrared optical absorption with light originating from a tunable diode laser [29]. This technique allowed the identification of the metastable NAD in presence of the more stable NAT under temperature and vapour pressure conditions near to those found in the polar stratosphere. Vapour pressures of Up, HN03, HC1, HBr over supercooled aqueous mixtures with sulfuric acid have been calculated using an activity model [56]. It provides a parameterized model for vapour pressures over the stratospheric relevant temperatures (185-235 K). 

For the solutes, simple salt solutions were selected, as they would provide a basic understanding of how non-idealistic solute particles would disrupt the liquid phase, thereby requiring the temperature to be lowered to make the transition from one phase to the other. The simple salts selected were chosen to have no net charge on the simulations systems and the pure Ewald summation was selected as the water model was parameterized under these conditions [21]. The salt solutions studied include a selection for size to charge ratio and 1 1 salt and 1 2 salt comparisons the salts studied included varying concentrations of NaCl, KC1, CaCl2, and MgCl2... 

To date, for pure water ice phases only second order invariants generated by projection on a small number of nearby bond pairs were needed. For example, for ice-Ih three second order invariant functions provided an accurate parameterization of the energy. We used those same three invariant functions with identical a coefficients to describe the pure water portion of the system with an L- and ionic defect. We incorporated 6 additional invariants of the form given in Eq. (2) involving a 6- and closeby c-variable. On physical grounds, we expect charge-dipole interactions to be important in the presence of ionic defects. The... 

More recently, Tomiyama and co-workers [154, 155, 156, 157] performed detailed experiments investigating the drag coefficient of a single bubble in a stagnant liquid. They proposed a drag coefficient parameterization which is split in three categories. These are pure, gently-contaminated, and contaminated systems, respectively. 

Voight, W., 2001, Solubility equUibra in multicomponent oceanic salt systems from t = 200 to 200°C. Model parameterization and databases. Pure Appl. Chem., v. 73, pp. 831-844. 

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