Pressure profile binned in x for water VLE

Hello All,

I have a water-vapor liquid equilibrium system of 1024 TIP4P/2005 water molecules. I have plotted the pressure profile for this system with normal pressure binned in x direction. For the plot, I computed the stress per atom in lammps and used the dump output of the compute in post processing.

In post processing , I have summed up the x , y and z components of the stress per atom compute separately, in each of the bins., i.e .,for atoms lying in bin 1, I have added the x , y and z stress/atom compute values seperately. Then, I divided the summed up x, y and z stress components by the bin volume, took it’s negative to get the final Pxx, Pyy and Pzz for the particular bin

Has anyone done similar work and could kindly tell me if the plot looks okay?

My input file is attached. Also, I have attached the same plot in three different formats.

Thank you.

Sincerely,
Neha Sinha
I.I.T Kanpur
India

PressureBinned-inX.txt (1.79 KB)

pressure _binned-x .jpg

Pressure_binned-x.tif (45.7 KB)

Pressure_binned-x.bmp (603 KB)

Hello All,

I have a water-vapor liquid equilibrium system of 1024 TIP4P/2005 water
molecules. I have plotted the pressure profile for this system with normal
pressure binned in x direction. For the plot, I computed the stress per atom
in lammps and used the dump output of the compute in post processing.

In post processing , I have summed up the x , y and z components of the
stress per atom compute separately, in each of the bins., i.e .,for atoms
lying in bin 1, I have added the x , y and z stress/atom compute values
seperately. Then, I divided the summed up x, y and z stress components by
the bin volume, took it's negative to get the final Pxx, Pyy and Pzz for the
particular bin

Has anyone done similar work and could kindly tell me if the plot looks
okay?

whether somebody here says "yay" or "nay" to your plots is not likely
to be of much value (and it is quite unlikely that somebody will do it
in the first place). if you want to have proper confirmation of your
work, try to reproduce data from the published literature.

axel.

Dear Axel,
I have done the literature search,but my plot does not match with the literature at the box edges. Meaning my normal pressure plot shows a steep high and low at the box edge (unlike literature) I have described in my earlier mail how I have done the plots. I am not able to understand the unusual edge behavior. If anyone has an insight into this then please enlighten me.

Thanks.neha.

Dear Axel,
I have done the literature search,but my plot does not match with the
literature at the box edges. Meaning my normal pressure plot shows a steep
high and low at the box edge (unlike literature) I have described in my
earlier mail how I have done the plots. I am not able to understand the
unusual edge behavior. If anyone has an insight into this then please
enlighten me.

please understand that what you are asking about is not really a
LAMMPS issue, but rather a question about how you have set up and are
analyzing your simulations. despite your description, there are many
unknowns and it is next to impossible to give any advice without
knowing *all* the details, having studied the publication(s) you are
referencing, *and* being interested in the specific research you are
doing. the person that most likely fits that description would be your
adviser and/or other members in your group.

axel.

While Axel is right in general, in this case I happen to recognize the specific issue you mention.
In short, what you are calculating is not strictly the normal pressure (which mechanical stability requires to be constant throughout the system).
I actually wrote about this in detail here:
section 2.6 in: http://pubs.rsc.org/en/content/articlelanding/2012/fd/c2fd20110k#!divAbstract
pp. 29-30 in: http://pubs.rsc.org/en/content/articlelanding/2013/fd/c2fd90042d#!divAbstract

Mario

Thanks Mario so much !

Regards,neha