[gmx-users] tau_t and tc_grps for v-rescale (2)

Felipe Pineda, PhD luis.pinedadecastro at lnu.se
Fri Sep 28 09:18:05 CEST 2012

Hi again,

I posted yesterday the query below, but have not received any feedback 
up to now. I would like to put my question in another way: in Justin's 
"CAP-15 in DPPC" tutorial he uses during NVT equilibration Bussi's 
thermostat (V-rescale) together with three separate coupling groups:

; Temperature coupling is on
tcoupl          = V-rescale                 ; modified Berendsen thermostat
tc-grps         = Protein DPPC SOL_CL   ; three coupling groups - more 
tau_t           = 0.1   0.1     0.1             ; time constant, in ps
ref_t           = 323   323     323             ; reference temperature, 
one for each group, in K),

Is this separate coupling needed at all taking into account that this 
temperature coupling method produces the correct coupling? Is it 
probably better to use a single coupling constant (system) and so avoid 
problems using this artificial correction to deal with the "hot solvent 
/ cold solute" artifact?

Could somebody kindly tell me how large could the coupling constant, 
tau_t, be? Is it OK to switch, e.g., from 0.1 to 0.3 ps after T 
equilibration is reached, i.e., during the production phase?

Many thanks again in advance and kind regards,


On 09/27/2012 03:49 PM, Felipe Pineda, PhD wrote:
> Hi,
> I'd greatly appreciate any general advice on the possibility to use 
> several (2 or more) tc_grps with v-rescale and how large could be 
> tau_t with this coupling method (is 0.3 ps still OK?).
> Many thanks in advance and best regards,
> Felipe

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