ATC: fix_modify AtC mesh create_nodeset

# fix_modify AtC mesh create_nodeset

## syntax

fix_modify AtC mesh create_nodeset <id> <xmin> <xmax> <ymin> <ymax> <zmin> <zmax>

- <id> = id to assign to the collection of FE nodes
- <xmin> <xmax> <ymin> <ymax> <zmin> <zmax> = coordinates of the bounding box that contains only the desired nodes

## examples

`fix_modify AtC mesh create_nodeset lbc -12.1 -11.9 -12 12 -12 12`

## description

Command to assign an id to a set of FE nodes to be used subsequently in defining boundary conditions.

## restrictions

## related

## default

Coordinates are assumed to be in lattice units.