[gmx-users] the temperature effect in the simulation

[Justin A. Lemkul]

He, Yang wrote:
> Hi all users,
> 
> When I change the temperature to try to get different disassociation about the two DNA's strands. But even I change the value of temperature by 0K in the mdp file ,
> 
> ; OPTIONS FOR WEAK COUPLING ALGORITHMS
> ; Temperature coupling
> Tcoupl                   = berendsen
> ; Groups to couple separately
> tc-grps                  = System
> ; Time constant (ps) and reference temperature (K)
> tau_t                    = 0.001
> ref_t                    = 300

I don't know if this is relevant or not, but a coupling constant of 0.001 is 
exceptionally short.  What is the timestep in your simulation?  Typically one 
sees tau_t = 0.1 with a timestep of 0.001-0.002 ps.

> ; Pressure coupling
> Pcoupl                   = no
> Pcoupltype               = isotropic
> ; Time constant (ps), compressibility (1/bar) and reference P (bar)
> tau_p                    = 0.5
> compressibility          = 4.5e-5
> ref_p                    = 1.0
> ; Random seed for Andersen thermostat
> andersen_seed            = 815131
> 
> It  will also disassociate .It is strange.

So the dissociation occurs at 0K and 300K?  Sounds like something is 
fundamentally flawed with your system setup.  How large is your box?  What force 
field are you using?

-Justin

> 
> Can anyone of you tell me what is the reason for that?
> 
> Thank you in advance.
> 
> Yang
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-- 
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Justin A. Lemkul
Graduate Research Assistant
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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