**From:** Sterling Paramore (*paramore_at_hec.utah.edu*)

**Date:** Tue Apr 03 2007 - 20:44:36 CDT

**Next message:**Luis Cunha: "Re: RE:Re: Help !!! ERROR: Atoms mooving too fast"**Previous message:**Peter Freddolino: "Re: Atoms mooving too fast ... still the problem"**In reply to:**Morad Alawneh: "Re: Pressure Discrepancy"**Next in thread:**Morad Alawneh: "Re: Pressure Discrepancy"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

Well, it's hard to tell from the graph, but it looks like your

decorrelation time is less than 100ps. If it is 100ps, then it means

you have ~ 100 independent pressure measurements (since your total

simulation time was 10ns). You stated in an earlier e-mail that the

mean pressure was 80 with a standard deviation of 360. With 100

measurements, the standard deviation of the mean is 36, meaning that

the pressure is 80+/- 70 at the 95% confidence interval. If the

confidence interval had been greater than 80, then I would have said

you didn't have to worry because the average pressure would be

indistinguishable from 0 (or 1) to within your measurement. However,

it looks like you are actually measuring a pressure that is not equal

to 1 (especially since the estimated CI is an upper bound). So I'm

not sure what's going on here.....

Actually, in the previous e-mail it looks like your x and y pressures

were significantly different than the z. Was this an NPAT simulation

where only the z-direction was couple to the barostat? If so, the z

pressure is NOT statistically distinguishable from 1, in which case

everything looks OK.

-Sterling

On Apr 3, 2007, at 10:39 AM, Morad Alawneh wrote:

*> Dear all,
*

*>
*

*> I am back to this problem with a graph showing the normalized
*

*> autocorrelation function of the instantaneous pressure. And
*

*> according to this graph, there is not that much of correlation ,
*

*> since its values are close to zero, and the pressure is stable that
*

*> is consistent with pressure vs time.
*

*>
*

*> Looking forward to hearing any suggestion.
*

*>
*

*> Morad Alawneh
*

*>
*

*> <acf_pressure.pdf>
*

**Next message:**Luis Cunha: "Re: RE:Re: Help !!! ERROR: Atoms mooving too fast"**Previous message:**Peter Freddolino: "Re: Atoms mooving too fast ... still the problem"**In reply to:**Morad Alawneh: "Re: Pressure Discrepancy"**Next in thread:**Morad Alawneh: "Re: Pressure Discrepancy"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

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