Ad hoc or transferable Force field fitting from ab initio calculations

10 Ad hoc or transferable Force field fitting from ab initio calculations 

Clearly, the issues of first principles and transferability are more pertinent to an essentially academic book such as the present one, while production details are more aptly included in internal technical manuals (heaven knows how much vital information is secreted in confidential company reports and thus hidden from the scientific community). The matter can be reformulated as follows the value of a parametric theory is directly proportional to the extension of the factual landscape to which it applies, and inversely proportional to the effort made in its development. Atom-atom formulations cannot yet be beaten in this respect. They apply with success to a wide scope of different problems and can give reliable theoretical estimates of crystal sublimation enthalpies and liquid evaporation enthalpies. And yet they are limited by their intrinsically scarce adherence to first principles, with a lack of contact between parameters and the implied physics. For these reasons, the future is not in their direction, and different paths must be sought, presumably in the direction of closer relationships between empirical force field parameters and quantum chemical data, considering that many molecular properties are nowadays more cheaply 

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