I used the example in.gcmc.h2o provided with lammps-3Mar20 to look at water vapor at different pressures and also look at the condensation. the only modification I made to the file is replacing pressure as GMC input instead of mu (chemical potential).
I find a notable problem with lammps results:
At low vapor pressures, I always have one water molecule present in the box. This one molecule is present even when pressure is equal to zero. there are two problems with this. 1- no matter what the box size is this single molecule always stays which means we will have different vapor densities for a given pressure. 2- this result doesn’t match with what I get from Cassandra which agrees better with experimental results. In the case of GCMC with Cassandra, I get a box which depending on vapor pressure has one or no water molecules which gives on average the density of water vapor. the ever-present water molecule gives a very high density on average compared to expected results for SPCE.
I searched and played with the input file but still don’t find where the problem is. I would be very thankful if anyone can give me an insight into this problem. I send the input files with this email however nothing changes compare to the original file.
Department of mechanical and process engineering
H2O.txt (535 Bytes)
in.gcmc.h2o (2.59 KB)