[gmx-users] NPT equilibration without pbc

Alex nedomacho at gmail.com
Sun Mar 5 07:29:56 CET 2017

Once again, please describe your system in more detail, because this 
isn't about Gromacs (which will correctly refuse pressure coupling for a 
finite, deep-nanoscale system). It is about the meaning of where 
pressure comes from in simulations and in reality.

In a realistic system "1 bar" would come from the air environment + any 
water evaporation in equilibrium with the liquid phase of the droplet. 
Even if you made your surface periodic, pressure coupling would have 
nothing to do with your finite droplet -- it would be in vacuum. 
Consider this work, for instance: 


On 3/4/2017 11:17 PM, Rajorshi Paul wrote:
> Hi Alex,
> Like I mentioned, my system consists of a water nano drop on a substrate. I
> need my system to be at 1 bar and 298 K. Without pressure coupling, I am
> unable to set the pressure to be at 1 bar.
> On 4 March 2017 at 22:18, Alex <nedomacho at gmail.com> wrote:
>> 1. Could you please provide a physical equivalent of a non-periodic NPT
>> system?
>> 2. Why can't you turn off the barostat, like GMX is asking?
>> Alex
>> On 3/4/2017 8:40 PM, Rajorshi Paul wrote:
>>> I am trying to simulate water nano droplet spreading on an FCC crystal
>>> substrate. I have not implemented periodic boundary conditions as my
>>> system
>>> is non-periodic. But when I tried to equilibrate my system in NPT
>>> ensemble,
>>> the program gives me a warning that I should set pressure coupling as
>>> "no".
>>> Is it possible to run NPT equilibration in non-periodic system?
>>> Thanks!
>>> Raj.
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