define group when I have used data file

Dear all
I am working on Al2o3 crystal and use data file. I have used topotools to crate data file.

I need to define some group by coordinate (region) to input some action like boundary, velocity & . . . on that groups of atom.
I can’ use region command.
please tell me how I can do that.

thanks

Dear all
I am working on Al2o3 crystal and use data file. I have used topotools to
crate data file.
I need to define some group by coordinate (region) to input some action like
boundary, velocity & . . . on that groups of atom.
I can' use region command.

you certainly can define a group based on a region.
check out the documentation for the group command.

axel.

Dear Axel
I have studied the group documentation and I just use region command before
it.
but when I use the data file it show me the error "Use of region with
undefined lattice".

Dear Axel
I have studied the group documentation and I just use region command before
it.
but when I use the data file it show me the error "Use of region with
undefined lattice".

yes it does, if you don't define a lattice *or* tell it to use "box units".
it is described in the region command documentation and has been
explained on this mailing list only a gazillion times.
this has *nothing* to do with using the read_data command.

axel.

*Thanks Alex*
*That is OK.*