[gmx-users] Order Parameter for HII phase

[Piggot T.]

Hi,

I don't believe this Chau paper is for deuterium order parameters (as I think you are most likely referring to) but is related to some of the other order parameter options in gmx order. The Vermeer paper you mention gives a good overview of deuterium order parameters and you can find more details in the papers referenced therein (e.g. the Douliez et al. and the Seelig et al. papers in particular).

For united-atom systems (as gmx order assumes), I believe the calculation is performed in gmx order using the "SCD = (2/3) Sxx + (1/3) Syy" equation (which is nicely derived in the 1998 Douliez paper: http://aip.scitation.org/doi/pdf/10.1063/1.476823) . The calculation requires an appropriate definition of the molecular frame of the system, where the z-axis is the bilayer normal.

Note that if you are calculating order parameters for unsaturated carbons (e.g. as in carbon-carbon double bonds), gmx order doesn't currently do this correctly as it requires a different calculation with a different molecular frame.

Cheers

Tom

________________________________________
From: gromacs.org_gmx-users-bounces at maillist.sys.kth.se [gromacs.org_gmx-users-bounces at maillist.sys.kth.se] on behalf of Justin Lemkul [jalemkul at vt.edu]
Sent: 23 February 2017 12:16
To: gmx-users at gromacs.org
Subject: Re: [gmx-users] Order Parameter for HII phase

On 2/22/17 9:51 PM, Mohsen Ramezanpour wrote:
> Dear Gromacs users,
>
> Unfortunately, I did not get any reply on this post.
>
> I was wondering if anyone is aware of the original paper on g_order so that
> I can understand the underlying algorithm of the options?
> I am not sure how to use it for HII phase order parameters.
>
> I found this article but I am not sure if these are the ones, as they do
> not describe g_order.
>
> "A new order parameter for tetrahedral configurations" by Chau and Hardwick
> (1998)

This is the reference given at the end of the gmx order help description.

-Justin

> and
> "Acyl chain order parameter profiles in phospholipid bilayers: computation
> from molecular dynamics simulations and comparison with 2 H NMR experiments"
> by Vermeer et al.
>
> Thanks in advance for your comments
> Mohsen
>
>
>
> On Sun, Feb 19, 2017 at 10:18 AM, Mohsen Ramezanpour <
> ramezanpour.mohsen at gmail.com> wrote:
>
>> Hi Everyone,
>>
>> I was wondering if someone has any suggestion on the following post,
>> please?
>>
>> Cheers
>> Mohsen
>>
>> ---------- Forwarded message ----------
>> From: Mohsen Ramezanpour <ramezanpour.mohsen at gmail.com>
>> Date: Thu, Feb 16, 2017 at 3:13 PM
>> Subject: Order Parameter for HII phase
>> To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>>
>>
>> Dear Gromacs users,
>>
>> I am interested in calculation of order parameter of lipids in a HII phase.
>>
>> I am not sure about the correct command to use. Which one of the following
>> should I use to be able to compare my data with deutirated NMR experiments?
>>
>> 1) gmx order  -f  md.xtc  -n  index.ndx  -s  md.tpr  -o  order.xvg  -od
>> deuter.xvg  -d z  -szonly
>>
>> or
>>
>> 2) gmx order  -f  md.xtc  -n  index.ndx  -s  md.tpr  -o  order.xvg  -od
>> deuter.xvg  -d z
>> (In this case, there are four columns of data (x, y, z for each carbon
>> atom).
>> The column 3 seems to be the same with when we include -szonly)
>>
>> or anything else?
>>
>> Corresponding available experimental data, I assume the second command
>> should be correct in my case . However, I am not sure x or y or what to use
>> for judging.
>>
>> Cylinders in HII phase are parallel to the Z axis in my system.
>>
>> Many thanks in advance for your comments
>> Mohsen
>> --
>> *Rewards work better than punishment ...*
>>
>>
>>
>> --
>> *Rewards work better than punishment ...*
>>
>
>
>

--
==================================================

Justin A. Lemkul, Ph.D.
Ruth L. Kirschstein NRSA Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 629
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441
http://mackerell.umaryland.edu/~jalemkul

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