fix nphug to simulate shock wave, weird species come out

Hello everyone,
I am using fix nphug with ReaxFF-lg to simulate the effect of shock wave on HMX molecules (a supercell including 64 beta-HMX molecules). But when I compressed the system to 80GPa and checked the output species, it is weird that there is super big molecule existing (C128H249O244N207),which is apparently contradictory to common sense . I used the default setting “fix 1 all nphug temp 1.0 1.0 100.0 z 800000 800000 1000.0”. Does anybody have any idea where this big molecule come from? Thanks.
G Wang

I assume you are using the fix reax/c/species to identify chemical species? If yes, you should know that the default bond order cutoff values are for normal, uncompressed systems. For compressed systems under shock, you should increase the bond order cutoff values.


Thanks for your reply. How much should I increase that cutoff value? Is there a reference?
Guangyu Wang

No, that is purely empirical. You should test these cutoff values against your compressed system.