AMBER Archive (2004)

Subject: Re: AMBER: Troubles in the NTP simulation: "vlimit exceeded".

From: David A. Case (case_at_scripps.edu)
Date: Tue May 04 2004 - 10:10:36 CDT

On Tue, May 04, 2004, lo Lille wrote:
>
> In our attemps to carry out NTP simulations of organic molecule
> consisting of about one thousand atoms, we meet steadily a trouble:
> "vimit exceeded".
> We add our controll parameters
>
> # Control section
> &cntrl
> ntwx = 500, ntpr = 500,
> ntt = 0, temp0 = 300.0, tempi = 300, tautp = 0.1,
                                         ^^^^^^^^^^^

This is too small; consider using a value 5 to 20 times larger.

Is your system already equilibrated? Note that you _must_ generally
equilibrate to 300K at constant volume before carrying out a constant
pressure simulation.

>
> &weight
> type = 'TEMP0', istep1 = 50501, istep2 = 51000, value1 = 300.0, value2
> = 0.0,
> &end

Why are you cooling a periodic, solvated system down to zero K? That generally
leads to nonphysical situations. (This is probably not related to the vlimit
error, but you should be sure that this is what you really want to do.)

...good luck...dac 

-- 

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David A. Case                     |  e-mail:      case_at_scripps.edu
Dept. of Molecular Biology, TPC15 |  fax:          +1-858-784-8896
The Scripps Research Institute    |  phone:        +1-858-784-9768
10550 N. Torrey Pines Rd.         |  home page:                   
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