# [lammps-users] Global cutoff

Hi,

Can anyone explain the difference between the global cutoff and cutoff radius.
For example

pair_style lj/cut 2.5
pair_coeff * * 1.0 1.0 1.1226

Here Rg = 2.5 and Rc = 1.1226. I don’t understand why one has to define two cutoff radii. If someone
can explain the what this means and the situations where one has to use it, I’ll be thankful.

Cheers
Srikanth

Hi,

Can anyone explain the difference between the global cutoff and cutoff

the global cutoff is the value that is used when you
do not specify a cutoff for an individual pair interaction.

For example

pair_style lj/cut 2.5
pair_coeff * * 1.0 1.0 1.1226

Here Rg = 2.5 and Rc = 1.1226. I don't understand why one has to define two
cutoff radii. If someone
can explain the what this means and the situations where one has to use it,

usually you only have one cutoff and thus only use the global one.
this way you can change it consistenly for many interactions
(e.g. in force field calcultions) and the local cutoff allows you
to selectively override this.

cheers,
axel.