Dear lammps authors and users

I am learning the airebo potential from the codes and the reference.

I found that the tricubic spline for conjugate term are inconsistent

in the two reference of the potential. Stuart et al. 2000, and

Brenner et al. 2002.

I realized that lammps follows Stuart's paper. And I have another

piece of code that follows Brenner's paper. I print out both splines

and summarize some of the discrepancies below

The discrepancy can also be easily observed in TABLE IX of Stuart and

Table 4 in Brenner

a) Most of the data are different by a factor of 2 in the two papers.

eg. i=1, j=2, k=4 Stuart: F=-0.0011689 Fx=0 Fy=0 Fz=-0.010022

Brenner: F=-0.0233778774 Fx=0 Fy=0 Fz=-0.020044

b) Some of the data F are different by a factor of 2, Fx, Fy, or Fz are

same.

eg. i=2, j=3, k=8 Staurt: F=-0.022355 Fx=0.062418 Fy=0 Fz=0

Brenner: F=-0.044709383 Fx=0.062418 Fy=0 Fz=0

c) if i or j > 3

eg. Brenner F(4 2 4)= F(3 2 4) = -0.04771

Staurt F(4 2 4)=0 F(3 2 4) = -0.022355

d) there are some wired values when i & j >3 in Starurt spline

eg. F(4.5 3.5 5)=4.09563 Fx(4.5 3.5 5)=3.18356 Fy=-12.2869 Fz=0

The discrepancy in spline introduce difference when simulate over

coordinated carbon structures. Can someone tell me if these

discrepancies has already been take cared in lammps or not? Can anyone

comments on the two reference works? I think Staurt is one of the

co-author in Brenner's paper, so they should use the same data set.

Thanks

Haibin

Haibin Chen Ph.D.

Mechanical Engineering Dept

Carnegie Mellon University

Pittsburgh, Pa, 15213