For the first problem, I did some careful tests, and find that it is the skin setting that really matters. With metal units ,AIREBO potential, carbon system, 1fs stepsize, initial velocity generate with random number, calculate on one processor of the same machine, equilibriate 1000steps, . the 1000step results are as follows( all without dangerous build )( 6DEC2008 lammps edition ):
Skin Step Atoms Temp PotEng KinEng TotEng
2.0 1000 9600 232.8161 -39095.203 190.16299 -38905.04
2.1 1000 9600 233.52098 -39092.148 190.73874 -38901.409
3.0 1000 9600 231.9985 -39074.087 189.49518 -38884.592
5.0 1000 9600 231.9985 -39074.087 189.49518 -38884.592
10.0 1000 9600 231.9985 -39074.087 189.49518 -38884.592
It seems that with the skin value increasing, the potential energy and total energy decrease, and when the skin is bigger than some value between 2.1 and 3.0. the results don’t change anymore. what it implies seems that when the skin is small, although there is no dangerous build, the result is not reliable, can you tell me why . I’m really puzzled, thank you!