Molecular diameter apparent temperature dependence

Clearly this goal may not be achieved through the use of the SPT. The very fact that we use the density of the liquid is equivalent to introducing structural information into the theory. Therefore, even if we find that the SPT is successful in predicting some thermodynamic quantities, it cannot be used to explain them on a molecular level. Thus the apparent success of the SPT, even when applied to complex fluids, is not entirely surprising. After all, injecting one macroscopic quantity into the theory is likely to produce other thermodynamic quantities that are at least consistent with the input information. For the computation of entropies, enthalpies, etc., one must also use the temperature dependence of the molecular diameter of the solvent. This quantity is also determined in such a way that the results are consistent with some measurable macroscopic quantity. In this way we further supply the theory with parameters which carry structural information on our particular system. 

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