Molecules interaction, assignment parameters

In this equation, all molecules are divided into four groups paraffins (P), olefins (O), naphthenics (N), and aromatics (A). The v values represent the volume fractions of each component used, while the fa values are the blending values, which were calculated for each of the molecular lumps shown in Table 2. Pure component octane numbers used are designated as ON/, but one should note that in the development of the model, 57 molecular lumps were made based on GC analysis, and pure component ONs were assigned to each lump, and not necessarily each pure component. The kt values are calculated interaction parameters between paraffins, olefins, and naphthenics, and are also shown in Table 2. Based on this equation, and knowing the composition and pure octane numbers of a fuel mixture, an estimation of the blending ON may then be made. 

The reference 4 authors discuss criteria that should be applied when describing molecules with these molecular mechanics programs. Some of these are as follows (1) Check the error file for interactions not in the parameter set, because some programs will assign a force constant of zero to unrecognized atom types (2) check all interactions generating >5 kJ/mol of strain to determine, for instance, whether that bond or angle really is that strained or whether there is a parameterization or molecular structure problem and (3) check the... 

Some researchers who use parameters derived from quantum chemical calculations on the whole solute molecule (Bodor, 1989) place their methods in a "theoretically-based" class. These are seen as preferable to methods which add the values assigned to structural parts, which then requires the assignment of interaction factors or corrections/ depending on how the parts are attached to each other. Fragment methods then are said to be in a purely empirical class and therefore obsolete. ... 

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