tersoff + Zbl

Is it possible that the SiC.tersoff.zbl file may not be properly implemented? When I think of the ZBL potential, I think of a repulsive-core potential for irradiation simulations. And if one splines the Tersoff to a ZBL potential, I would think that the potential should retain (most) of the characteristics of Tersoff at ambient conditions. However, I find that the density with Tersoff + ZBL actually increases than with just Tersoff. To me, I cannot think of a reason why this would happen. ZBL, if anything, would push the atoms further apart from one another due to its repulsive nature.

Also, I analyzed the Threshold displacement energy for both Tersoff and Tersoff + ZBL and I find that Tersoff matches other literature findings, but Tersoff + ZBL seems to not match other literature findings. Perhaps there is something wrong?

Or of course the other possibility is that I am wrong in my interpretation. I am somewhat confident as I have been able to reproduce results with Tersoff, but not Tersoff + ZBL.

So there may be a bug, or maybe it’s just me.

Ben

Well, SiC.tersoff and SiC.tersoff.zbl have different paraemters… That is why you get different results.

Ray

Of course they have different parameters, one has the ZBL potential in it and the other does not. So, of course, the parameterizations are slightly different. I did not expect the results to be the same, and I do not think that I said I was expecting them to be the same.

Let me try to clarify. As implemented, the Tersoff potential matches other Threshold displacement energies in the literature that just used Tersoff potential. But Tersoff + ZBL does not match other literature findings for TDE that used Tersoff + ZBL. Does my point make sense now? I am just trying to say that one potential reproduces results of other literature with that respective potential, and the other does not, with that respective potential.

My other point was to just say that the results for Tersoff + ZBL (I would think) would have closer values to just Tersoff at ambient conditions (not to say that it has to be). If anything, I would expect Tersoff + ZBL to have a stronger repulsive core, thus forcing the atoms further apart, but this is not the case.

Of course they have different parameters, one has the ZBL potential in it
and the other does not. So, of course, the parameterizations are slightly
different. I did not expect the results to be the same, and I do not think
that I said I was expecting them to be the same.

Of course, but their Tersoff parameter are already different.

Let me try to clarify. As implemented, the Tersoff potential matches other
Threshold displacement energies in the literature that just used Tersoff
potential. But Tersoff + ZBL does not match other literature findings for
TDE that used Tersoff + ZBL. Does my point make sense now?

I am afraid not. Different Tersoff paramters (regardless of the ZBL part)
will give you different properties for the same Tersoff crystal at
equilibrium.

I am just trying to say that one potential reproduces results of other

literature with that respective potential, and the other does not, with
that respective potential.

My other point was to just say that the results for Tersoff + ZBL (I would
think) would have closer values to just Tersoff at ambient conditions (not
to say that it has to be).

This expectation is correct provided that Tersoff parameters in both files
are exactly the same. However, they are not.

Ray

Ok, now I understand your point more so. I was not aware that the Tersoff parameters were based on different papers. OK, I will look into this. Thanks for the help

Ben