[lammps-users] deformed box after npt run with pressure control style "xyz"

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1

Hi all:

I got a deformed box after npt run with pressure control style “xyz”.

At the beginning, the lengths abc for the box are 28.84:28.84:74.67= 0.39: 0.39:1

At the end, the lengths abc for the box are 32.94:32.94:73.64= 0.45:0.45:1;

So the ratio of my box changes from 0.39 to 0.45. It looks strange!! If I continue the running it will change still.

The command I used is : “fix npt GB npt/asphere 2.99 2.99 0.1 xyz 4.4 4.4 100 dilate partial”. The model includes a frozen LJ cylinder and many GB particles. The total box size is much bigger than that of the cylinder.

Any comment will be appreciated. The version of current Lampps I used is 27 Jan 09. Followings are part of my log file.

…

fix npt GB npt/asphere 2.99 2.99 0.1 xyz 4.4 4.4 100 dilate partial

Resetting global state of Fix npt Style npt/asphere from restart file info

run 360000

Memory usage per processor = 4.66886 Mbytes

Step Temp a_temp Press Volume PotEng KinEng Lx Ly Lz Pxx Pyy Pzz Pxy Pxz Pyz

0 2.0232614 2.9235608 5.5379974 62108.72 -5.5149004 3.0347186 28.839654 28.839654 74.674529 5.6099543 5.7951015 5.2089364 -0.057484868 0.14193013 -0.017237353

30 2.1563292 3.1243784 5.7688861 62119.892 -5.4043559 3.2343088 28.841501 28.841501 74.678397 5.9118363 5.9017536 5.4930685 0.13536497 -0.14339967 0.016970861

…

204060 2.6092787 3.8000782 3.970928 81345.836 -2.2471938 3.9136944 32.441992 32.441992 77.289463 4.0214534 4.0028488 3.888482 -0.094718793 0.0033341361 0.06431118

204090 2.64307 3.8400316 3.8991591 81335.156 -2.2749352 3.9643783 32.440705 32.440705 77.28545 4.0484775 3.870633 3.7783667 0.042184151 0.087694845 -0.022122278

…

359970 2.6277976 3.7813559 4.0555479 79899.849 -2.3663354 3.941471 32.939936 32.939936 73.637739 4.0661648 4.176934 3.9235448 -0.021508017 0.055192892 0.044801632

360000 2.6099786 3.7717531 4.0080583 79903.334 -2.3645005 3.9147441 32.94055 32.94055 73.638209 4.2167264 4.0485693 3.7588794 0.0083517472 -0.031063075 0.031805401

Loop time of 123058 on 8 procs for 360000 steps with 17492 atoms

Best wishes,
Yours Kitty.

2

Please add this print statement to fix_npt::remap()
and re-run for 1000 steps and let me see the results. I think the 3 dilation
factors (for x,y,z) should be the same as each other on
every timestep, so I don't see how the box can change as
your output indicates.

      domain->boxlo[i] = (oldlo-ctr)*dilation[i] + ctr;
      domain->boxhi[i] = (oldhi-ctr)*dilation[i] + ctr;
      printf("BOX DILATE: %d %g %g\n",i,dilation[i],oldhi-oldlo);

Steve

2009/2/11 Kitty Ji <[email protected]...>: