Re: [ESPResSo] orientational order parameter

[Olaf Lenz]

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Hi!

martina pannuzzo wrote:
> a few days ago, i sent a mail but i got no aswer;maybe i was unclear.
> I am simulating the lipid vesicles with the mbtools but the order
> parameter is not convincing.in the state more ordered i get a
> orientational order parameter value close to the lowest possible -0,45.
> when the temperature increase the oop increase.
> there appears to be a reversal of the sign.
> I attached a picture to make the idea.

First, let me state that I am not an expert on the mbtools, but I did
work on membranes during my PhD thesis.

I do not see any error in what you describe. To my understanding, the
nematic order parameter of a vesicle should be close to -0.5.
Have a look at the definition: If all lipids point to the same
direction, S has a value of 1. If all lipids point to random directions
(and a vesicle can be seen as that), S whould be -0.5.

The parameter is not defined locally, i.e. it does not take into account
the nieghbourhood of lipids. Instead, it is defined globally over all
lipids.

So, where is the problem?

Best regards
        Olaf
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