Dear Lammps users,
Today, I noticed some interesting features in the potential directory regarding tersoff parameters for Silicon and Carbon. Please correct me if I am wrong. Any comments will be appreciated
Firstly, the parameters for Si Si Si in Si.tersoff and SiC.tersoff are different. Probably they were taken from different sources but I think a reference would be appropriate for other users. For SiC.tersoff the reference is PRB,39, 5566 - 5568 (1989). In this file, the parameters for Carbon are also taken from the same reference
Secondly, the equation used in the above paper is a little different than the one which lammps uses. The difference is in Fc®.
The paper uses the terminology of Rij and Sij which are similar to R-D and R+D for the lammps tersoff equation. However, the parameters R and D in the SiC.tersoff file has been written as Rij and Sij (taken from the paper directly).
Rij = 1.8 and Sij=2.1
which makes R=1.95 and D=0.15 for the lammps tersoff input file instead of 1.8 and 0.3 which are written in the file.
Rij = 2.7 and Sij=3.0
which makes R=2.85 and D=0.15 for the lammps tersoff input file instead of 2.7 and 0.3 which are written in the file.
and then the cross parameters can be evaluted from these. I am not sure how much difference this will make to a particular simulation, but should be worth letting fellow lammps users know.
Please correct me if I am wrong anywhere.