Dear LAMMPS Users,
Basically, I want to perform a non-reactive MD simulation by ReaxFF at a very high temperature (i.e. 2000K or 3000K) to equilibrate the system. More specifically, it is about hydrocarbon oxidation (say methane oxidation) ReaxFF simulations. However, it is obviously that the system will react at such a high temperature. I searched the LAMMPS mail list and found several similar questions asked by other users but I am still very confused and don’t know how to do it.
I read several relevant papers doing non-reactive MD simulation to equilibrate the hydrocarbon oxidation system and got below descriptions:
“The initial system was firstly equilibrated at 298 K for 50 ps to get the reasonable initial configuration. After the equilibrium, the system temperature was further raised to 2000 K from 298 K within 50 ps at uniform rate. The NVT canonical ensemble was employed for these two stages to control the volume and temperature of the system. During the first two stages, no reaction between molecules was observed. After these two stages, microcanonical ensemble (NVE) was used to explore the detailed reaction process between CH4 and O2.”
“All the systems were minimized by molecular dynamics at low temperature (5 K) using the NVE ensemble. Then, they were equilibrated with the NVT ensemble for 10 ps at 1000 K using a time step of 0.1 fs.”
“The simulation procedure began with minimization of each system using low-temperature MD. Next, the system was equilibrated at 2500 K for 100 ps using a NVT MD simulation with a MD time step of 0.1 fs. During the equilibration simulations, the C-O and H-O bond parameters were switched off to prevent reactions from occurring during the equilibration of the system.”
“Reactions between O-C and O-H were prevented during the 100-ps equilibration period by eliminating the bond parameters describing these interactions from the force field.”
Therefore, based on the above descriptions, I believe that there is a certain way to perform a non-reactive ReaxFF simulation especially by switching off or eliminating some parameters. I am wondering that anyone know how to do it? It seems that I need to modify the force field file a little bit. My another question is that why point 3 & 4 only turn off the C-O and H-O reactions but not all bond reactions?
Sorry for the long question. I would appreciate it very much if anyone can help me with it. Many thanks in advance!