[Ifeffit] Cumulant expansion fittings

Scott Calvin SCalvin at slc.edu
Wed Jan 21 21:30:28 CST 2009


You're right--3 dimensions ruins my symmetry argument. My mistake.

On the other hand, I still suspect that there exists a realistic case  
where forcing the third cumulant to zero cause a much smaller increase  
in chi-square than forcing the fourth cumulant to zero; e.g., a broad,  
flat radial distribution function.

For those of you out there who are relative novices, this is an  
entertaining and informative discussion, but I don't want to lose  
track of the practical point:

It is very rare to find a system where the fourth cumulant is both  
necessary and sufficient. Either the potentials are close enough to  
harmonic that the fourth cumulant makes little difference, or they are  
so far from harmonic that the fourth cumulant alone is not enough.

--Scott Calvin
Sarah Lawrence College

On Jan 21, 2009, at 10:11 PM, Frenkel, Anatoly wrote:

> Thus, I am pretty much convinced, unless there is some mistake in my  
> reasoning, that no case exists in 3D with a zero third cumulant.

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