Dear LAMMPS users,
I am interested in simulating a liquid/vapor interface, but I am running into a strange problem. My system consists of N=256 rigid molecules, each molecule consisting of three Lennard-Jones atoms. Atoms within a molecule have no interactions with each other. Only different molecules interact with each other.
I have successfully equilibrated my system in a cubic volume, but when I introduce an interface by expanding the zlo, zhi values and run fix rigid, my system breaks down: the total energy is no longer conserved the kinetic energy increases without bound. (Sometimes the total energy decreases before increasing later.) The potential energy, however, does not change much. When I take the same input configuration file but change the zlo and zhi values to their original values, the system is stable.
I've tried the following:
- I've checked for rigid molecules across the z-boundaries, and after fixing that so that the molecule is 'whole' in the configuration file, I find that the system blows up
- I've simulated a system of 256 LJ monomers, and this system is stable after the expanding the zlo,zhi values.
- I've compiled lammps on a different architecture machine (64bit versus 32 bit) and the systems blow up
I've actually looked at several systems, with both charged and uncharged atoms, and of various system sizes (N=256, 500, 864). What is confusing is that my systems do not always blow up; only some blow up but others can be perfectly stable, exhibiting the expected behavior after the introduction of an interface. I basically cannot predict whether a system will blow up or not upon the introduction of an interface, despite the many different experiments I've run.
Based on my studies, I think either there is some implicit assumption somewhere in lammps that I am violating by extending zlo and zhi (or any boundary since I've also tried changing x and y boundaries), or maybe there is a bug somewhere??
Attached are the configuration file and input file for the simplest system that behaves strangely when an interface is introduced.
I would really appreciate any input on this! Thanks in advance,
in.sample (606 Bytes)
sampleConfig.txt (72.6 KB)