|float[dimensionless scalar variable]
The parameter is not used with vsfoldX anymore, but historically, we get in the following way. The value obtained in McKenzie-Domb model is . A Gaussian distribution function would have , and a large weight such as used in the adjusted Jacobson-Stockmayer equation in the Turner energy rules would yield (for ). There would be reasons to think that the polymer exists as a reduced dimensionality meaning that t could perhaps reduce the weight to a two-dimensional Gaussian expression such that . Therefore, a reasonable range for to would at most be . As we have argued in other places, values at the extremes seem inappropriate at best, and values somewhere in the middle would make the most sense.
These parameters can now be used in conjunction with Flory's polymer-solvent interaction model.
There is some appeal to using the parameter in these equations because in the original definition of we used only Gaussian functions. The form of (1) has the appeal of a clean symmetric looking function, however the meaning of the self-avoiding walk contribution is somewhat obscured. With the MMDF model, the parameter is clearly suggestive of an excess volume (indeed the expression is an indication of a fractal volume!). We may eventually move in the direction of using as the defining parameter, but because the Jacobson-Stockmayer equation used in Mfold and the Vienna package is so common with the , it seems best to consider that in any discussions about parameterizations.