On 12/6/12 5:26 AM, Erik Marklund wrote:

5 dec 2012 kl. 17.26 skrev Justin Lemkul:



On 12/5/12 11:21 AM, Kavyashree M wrote:
Sir,

Thank you for your suggestions. I decided the cutoff based on
RMSD convergence. I will calculate at different time intervals.
Running multiple simulation is definitely the best suggestion but
due to time and machine constraint it would be difficult. Instead
I have two mesophilic simulations. But Is there any other way
by which I can prove this point?


Not using single trajectories.  Your job is to convince reviewers that your 
work is sound.  A single trajectory is not convincing, at least to any reviewer 
that does his or her homework :)


I don't think that the use of single trajectories is necessarily "wrong", as 
long as they are sufficiently long. It's usually the amount of sampling that is the 
crucial point, no?


Well, long simulations have issues too - http://dx.doi.org/10.1016/j.bpj.2010.04.062.

That said, there's probably not one single answer here. I am generally leery of anyone trying to make arguments based on a single trajectory, especially one that is relatively short by modern standards. Indeed, the simulation needs to be sufficiently long to potentially observe the phenomenon of interest, and that simulation should be converged and of adequate length to collect reasonable statistics. I think, from a practical standpoint, several simulations of intermediate length will give you better insight than a single simulation of any length. Certainly in my work on amyloid peptides, multiple trajectories of considerable length are prerequisite; most other papers get (rightly) thrown out immediately. In the case of well-folded proteins whose behavior is more predictable, you can probably get more information from a single high-quality trajectory.

In the present case, where a simulation of modest length is not agreeing with (presumably) experimental data, I think sampling or convergence is a major concern. Had the trajectory reproduced the expected behavior, it's less of an issue.

-Justin

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

Justin A. Lemkul, Ph.D.
Research Scientist
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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