I have been doing simulations with rigid water models, and have been having some issues with the fix rigid and related commands. First of all, I cannot seem to fix the temperature separately from the rigid command, i.e. if I use the commands
fix 1 all rigid molecule
fix 2 all nvt temp 298.0 298.0 100.0
the results are very strange (like the radial distribution function for bulk water for example is erratic and completely wrong). If I use the rigid/nvt command, the results are normal
fix 1 all rigid/nvt molecule temp 298.0 298.0 100.0
However, I want to use the rigid/small command, because supposedly it is faster for many small molecules. The rigid/small/nvt command is not actually supported, so I would like to run something like
fix 1 all rigid/small molecule
fix 2 all nvt temp 298.0 298.0 100.0
But as I mentioned, this gives very strange results.
I have been doing simulations with rigid water models, and have been having some issues with the fix rigid and related commands. First of all, I cannot seem to fix the temperature separately from the rigid command, i.e. if I use the commands
fix 1 all rigid molecule
fix 2 all nvt temp 298.0 298.0 100.0
the results are very strange (like the radial distribution function for bulk water for example is erratic and completely wrong). If I use the rigid/nvt command, the results are normal
fix 1 all rigid/nvt molecule temp 298.0 298.0 100.0
However, I want to use the rigid/small command, because supposedly it is faster for many small molecules. The rigid/small/nvt command is not actually supported, so I would like to run something like
Fix rigid/small/nvt is available in the current version of LAMMPS. Please check the online documentation.
fix 1 all rigid/small molecule
fix 2 all nvt temp 298.0 298.0 100.0
But as I mentioned, this gives very strange results.
You would have to use a non-time-integrating thermostat for this.
Sorry, I did write rigid/nvt/small, sorry about that typo. I do see it in the documentation, but it doesn’t work when I try it, and is not listed in the “style_fix.h” file. I am using lammps-1Feb14 distribution, so I think it is fairly recent.
Can you explain what you mean by non-time-integrating thermostat and normal integrator? Thanks.
This may also be related to another bug I encountered. I found that using a Berendsen thermostat gave very strange results earlier. Is that a non-time-integrating thermostat? Perhaps I need to understand this difference.
-Teddy
Hi all,
Thank you for the quick responses.
Sorry, I did write rigid/nvt/small, sorry about that typo. I do see it in the documentation, but it doesn’t work when I try it, and is not listed in the “style_fix.h” file. I am using lammps-1Feb14 distribution, so I think it is fairly recent.
No. Plenty of updates since then.
Can you explain what you mean by non-time-integrating thermostat and normal integrator? Thanks.
Please reread the manual. It explains these things in detail.
This may also be related to another bug I encountered. I found that using a Berendsen thermostat gave very strange results earlier. Is that a non-time-integrating thermostat? Perhaps I need to understand this difference.
Berendsen is has problems as is documented in the published literature and also explained several times on this mailing list.