AMBER Archive (2007)

Subject: Re: AMBER: correlation time

From: David A. Case (case_at_scripps.edu)
Date: Tue Dec 04 2007 - 12:40:20 CST

On Tue, Dec 04, 2007, Tuncel, Aytug wrote:
>
> In the "Gohlke H, Kiel C, Case DA. Insights into protein-protein binding
> by binding free energy calculation and free energy decomposition for the
> Ras-Raf and Ras-RalGDS complexes. J Mol Biol. 2003 Jul
> 18;330(4):891-913" paper there is a section:
> " ... the energy values obtained for 150 adjacent snapshots extracted
> from 3 ns of production runs should be nearly uncorrelated, since the
> correlation times for relaxation of effective energy ?uctuations (1 ps)
> are shorter than the time-interval (20 ps) used for snapshot
> extraction."
>
> I wonder how the correlation time is calculated (how is the 1 ps value
> calculated), or how can we find that the extracted snapshots are
> uncorrelated?
>

You just take the MM-PBSA enthalpy estimate time series, and compute an
autocorrelation on it, using your favorite program. I think we used xmgrace
for this purpose, but many other stat programs will do the same thing. Or,
write your own perl or awk script, and you will have the added benefit of
really learning how this is done.

...dac
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