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Re: [ESPResSo-users] volume change and reported Tcl analysis quantities

From: Arash Azari
Subject: Re: [ESPResSo-users] volume change and reported Tcl analysis quantities
Date: Mon, 17 Feb 2014 03:22:29 -0800 (PST)

Hi Florian,

Thank you very much for your reply.
I am using the 'change_volume' command.
Instead of using 'integrate 0', if we just continue the simulation, does the 
normal 'integrate' command recalculate the force and other quantities? Like 
simulation where at each step we should recalculate the forces, 
positions and so on. I mean something like this:

for { set frame 1 } { $frame <= $num_frames } { incr frame } {
change_volume   $L_new_z    z
integrate       $steps_per_frame
[analyze pressure total]

Thank you,

Best regards,

Arash Azari

On Monday, February 17, 2014 12:41 PM, Florian Weik <address@hidden> wrote:

volume change by changing the particle positions and resetting the box size. 
There is is a command for that called 'change_volume' which does just that.
All quantities that depend on the volume, e.g. the pressure and stress tensor, 
will only be physical again if you recalculate the forces. You have to be aware
that the volume change in its own does not cause an energy or force 
recalculation. You have to this (e.g. integrate 0) before you have meaningful 
values again.


On Mon, Feb 17, 2014 at 11:09 AM, Arash Azari <address@hidden> wrote:

>I appreciate any comments on the following questions.
>Suppose we change the volume of the simulating system during a long and slow 
>process in two different ways;
>first change the simulation box dimensions which does not conserve the total 
>volume (shrinking or expanding)
>second keeping the volume fixed and changing the box size (increasing one 
>length and decreasing the rest accordingly).
>- Volume change works just by relocating the position of the all
>particles, without changing other quantities like velocities and so on,
>is it correct?
>- Does the reported quantities from Tcl analysis like pressure, force,
>temperature are physically meaningful during the change process? I mean
>for example the reported pressure during the change is a real physical
>quantity or it includes some artefact of the volume change process.
>Thank you very much,
>Best regards,
>Arash Azari 

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