[gmx-users] Scd or -Scd?

Thomas Piggot t.piggot at soton.ac.uk
Fri Jul 14 19:48:04 CEST 2017

That should have read |Scd| and not [Scd] in the last sentence.

On 14/07/17 18:40, Thomas Piggot wrote:
> As far as I'm aware (and happy to be corrected if someone knows 
> better) it is simply a convention that stems from the fact that the 
> signs of the order parameters were not originally determined from 
> experiments and so were reported in these works as |Scd|. Given that 
> the order parameters of the lipid tails are pretty much always 
> negative, it makes sense to show -Scd to keep the plots looking the 
> same as those that report the absolute values of the Scd.
> That said, you should be careful with reporting the absolute values 
> though as the order parameters (Scd) can theoretically vary between 
> -0.5 and 1. Indeed with some force fields (e.g. ones with unsaturated 
> double bonds) you can have order parameters that do cross 0 (i.e. will 
> be plotted incorrectly if you report [Scd]).
> Cheers
> Tom (not Justine!)
> On 14/07/17 18:01, m g wrote:
>> Dear Justine,Why are the order parameter data reported in articles as 
>> -S_CD (minus S_CD)?
>> Thanks,Ganj

Dr Thomas Piggot
Visiting Fellow
University of Southampton, UK.

More information about the gromacs.org_gmx-users mailing list