Hi,
In a tensile simulation of CNT, I’m getting the total energy as negative when I use SiC tersoff potential…
The simulation is running fine… But what does it mean to get the total energy as negative…
Regards
Not really shocking! 
It is probably because the CNT atoms are bound to each other by the attractive part of the inter-atomic potential you are using. That is to say that they are in a potential well (with a negative potential energy) of the neighboring atoms. Print out the potential energy and kinetic energy and convince yourself abt this. This would happen even in a non-tensile simulation of any solid with any potential which has an attractive part and retains the solid phase.
Think about -> Would you expect the same if you simulate a liquid? a gas?
OR did I misunderstand your question?
Manoj