Universal forcefield

The EHM will require far fewer parameters. This is easy to see, because each atom requires just one parameter for each valence atomic orbital. For C, for example, we need an ionization energy for the 2s, and one for the 2p orbitals, just two parameters (strictly, valence state ionization energies, VSIEs - see Harder Question 9).3 Each H needs only one parameter, for its Is orbital. So for an EHM program that will handle hydrocarbons in general we need only three parameters (as in Hoffmann s pioneering paper on hydrocarbons [1]). In contrast, an early but viable molecular mechanics forcefield limited to alkanes had 26 parameters [2]. The Universal Force Field, which sacrifices accuracy for wide applicability, has about 800 parameters, and the accurate and quite broadly applicable Merck Molecular Force Field 1994 (MMFF94) has about 9,000 parameters [3]. 

There is a way of manipulating matter and energy so as to create what modern science calb a force-field. This forcefield acts upon the observer and puts him in a privileged position in relation to the universe. From this privileged position, he has access to realities which are normally concealed from us by time and space, matter and energy. This is what we call the Great Work. 

Atom-atom two- or three-body interactions of these sorts are incorporated within available forcefields that have been derived to fit empirical data. Commonly used forcefields include the universal force field (UFF) and the constant valence force field (CVFF). ... 

Here, Nq refers to the preferred coordination number of the central ion and the empirically determined term in square brackets accounts for the effect of polarization (oa, Ox refer to the absolute softness values of the cation and anion, respectively) as well as the influence of higher coordination shells. Practically, the coefficients /i = 0.9185 and /2 = 0.2285 eV were derived by comparison with the parameters used in other empirical force fields such as the universal force field (UFF) [27]. The level of agreement for the resulting values with the established UFF forcefield can be judged from Fig. 7 (/ 0.95). 

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