Hello,
In the SPC Water Model from LAMMPS manual (8.4.6. SPC water model — LAMMPS documentation), they wrote: run 0 post no, and I get a warning that the atoms wont move. When it is removed, the warning message disappear…Why ?
Please note that in LAMMPS input file the order of commands matters. 5.1. LAMMPS input scripts — LAMMPS documentation
There is no fix defined that does time integration of atoms (like fix nve or fix nvt) when the “run 0” command is issued. Hence the warning. However, the warning is harmless, since with 0 steps the atoms will not move anyways. This command is usually issued in this way to initialize forces and update the number of degrees of freedom so that a following “velocity” command can correctly determine the velocities corresponding the temperature. For this specific input, however, the run 0 command is unnecessary and can be removed without a problem.
In fact, those how-to examples are about to be updated with revised settings that are closer to best practices for features and settings of the current version of LAMMPS.
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Thank You a lot !