AMBER Archive (2007)

Subject: Re: AMBER: temperature fluctuation in REMD

From: priya priya (priyaanand_27_at_yahoo.co.in)
Date: Fri Jul 20 2007 - 07:11:17 CDT


Dear Sir,
In normal MD there is not too much fluctuation in temperature specified that is +10 from the temp0. but here more than 30degree fluctuations are seen, and if i draw the specific heat graph from the potential energy and temperature it is a flat curve without any peak.
>From my procedure is there any mistake u an observe.
Thanks,
Regards
priya

Carlos Simmerling <carlos.simmerling_at_gmail.com> wrote: is this different from what you see in normal MD for
this system using this thermostat and temp0?
in other words, is this expected behavior for REMD, or
do REMD and MD differ?

On 7/20/07, priya priya
 wrote:
> Dear All,
>
> I am doing replica exchange method using implicit solvent, looking into the
> results summary.TEMP created by using reminfo file i found that the
> temperature is fluctuating a lot even though i am using langevin
> thermostat.I started from temp range 273K to 373K but in the output file
> there are temperature 402 K and above also.
> Method i followed is as under with the input files:
> 1) minimized the linear structure generated by Xleap: input file:
> Stage 1 - minimisation of am15-42 in implicit solvent
> &cntrl
> imin=1, maxcyc=5000, ncyc=2500,
> cut=999., rgbmax=999.,igb=1, ntb=0,
> ntpr=100
> /
>
> 2) heated the system for different temperatures which could act as the
> starting conformations for the Replica exchange method. input file was (only
> temp different in files):
> am15: 100ps MD in implicit solvent
> &cntrl
> imin = 0,
> ntb = 0, igb = 1,
> cut = 10,
> tempi = 373.715, temp0 = 373.715,
> ntt = 3, gamma_ln = 1.0,
> nstlim = 50000, dt = 0.002,
> ntpr = 50, ntwx = 50, ntwr = 50
> /
> 3) REMD using the reference rst from from the previous step at different
> temp
> input file (different temp for different replicas):
> &cntrl
> imin = 0, nstlim = 100, dt = 0.002,
> ntx = 5, tempi = 360.893,temp0 =360.893,
> ntt = 3, tol = 0.0000001,
> ntc = 2, ntf = 1, ntb =0,
> ntwx = 5, ntwe = 0, ntwr = 5, ntpr = 5,
> cut =10.0, scee = 1.2, ibelly =0,
> ntr = 0, gamma_ln = 1.0,offset = 0.09
> nscm = 500, igb = 1,
> irest = 1,numexchg = 50000, repcrd = 0,ntave = 0,
> /
>
> System is running fine with showing exchanges in the log file that has been
> created, but if i extract output for the various repinfo file created for
> different replicas, i found strange fluctuation in temp which are not the
> range given.
> Will anybody see error in my steps and my input file.
> Suggestion are welcomed.
>
> Regards
>
>
> ________________________________
> Unlimited freedom, unlimited storage. Get it now
>
>
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