Questions about Pair Potentials

Hi Lammps-users, I have a few questions:

I’m creating my own potential by editing pair_lj_smooth potentials
(the two are similar and I didn’t want to start from scratch). I don’t
quite understand what the “offset” stored in the offset array does.

I’m also not clear on what a tail correction is.

Also, what’s the purpose of the single function/method.

Thanks,
Avik Mondal

For pair potentials whose energy does not

go to zero at the cutoff, but to epsilon, the

pair_modify shift yes command adds epsilon

to each pairwise interaction, to “shift” the

potential to 0.0.

Offset = the epsilon value for each type pair.

Steve

Hi Lammps-users, I have a few questions:

I'm creating my own potential by editing pair_lj_smooth potentials
(the two are similar and I didn't want to start from scratch). I don't
quite understand what the "offset" stored in the offset array does.

the ​offset array corresponds to the pair_modify shift ​option.

I'm also not clear on what a tail correction is.

​this is a correction for the pressure due to LJ interactions that are cut
off.

​please see the documentation of the pair_modify command for details.​

http://lammps.sandia.gov/doc/pair_modify.html

​and the documentation and source code of lj/cut​ and pair.h and pair.cpp

Also, what's the purpose of the single function/method.

​it is used by a number of features in LAMMPS, where the interaction of an
individual pair of atoms has to be computed and not the entire list of
neighbors for all local atoms, e.g. in compute group/group.​

​the value of the variable single_enable tells the ​rest of LAMMPS, whether
it is a available or not. again, this is best understood by reading through
the source of pair.h, pair.cpp and pair_lj_cut.cpp

axel.