LIGGGHTS® 4.X vs. LIGGGHTS® 3.X - syntax changes

Introduction:

This is a short outline of the most important changes in LIGGGHTS® 4.X compared to LIGGGHTS® 3.X regarding the syntax of major commands. The motivation for these changes was to make the script language more readable and to improve extendability (in the sense of object oriented programming) with respect to modelling approaches.

Commands covered by this tutorial:

  • fix nve/nonspherical

  • fix multisphere

  • fix concave

  • fix couple/cfd/force

  • fix nve/cfd_cn

Changes in syntax for each command:

Changes are indicated as follows

OLD: old_syntax
NEW: new_syntax

where old_syntax refers to the syntax used in LIGGGHTS® 3.X and before, and new_syntax refers to the syntax used in LIGGGHTS® 4.X.

fix nve/nonspherical:

OLD: fix ID group-ID nve/superquadric
OLD: fix ID group-ID nve/convexhull
NEW: fix ID group-ID nve/nonspherical

All integrators for atom types superquadric and convexhull used to require a specialized integrator. These integrators have now been combined in a single fix nve/nonspherical to improve code quality and simplify the input script generation

fix multisphere & fix concave:

OLD: fix ID group-ID multisphere
NEW: fix ID group-ID multisphere
     fix ID group-ID nve/nonspherical

OLD: fix ID group-ID concave
NEW: fix ID group-ID concave
     fix ID group-ID nve/nonspherical

Previously the fix multisphere would also contain the multisphere integrator and the same is true for fix concave. This is no longer correct due to the rewrite mentioned above. Because of this it is now necessary to specify an integrator explicitly. As all non-spherical integrators have been unified into one fix this is the same fix nve/nonspherical.

It was possible in 3.X to specify a fix multisphere/nointegration the same can now be achieved by using a fix multisphere without the nonspherical integrator.

fix nve/cfd_cn & fix couple/cfd/force:

OLD: fix ID group-ID couple/cfd/force/implicit

fix ID group-ID nve/sphere

NEW: fix ID group-ID couple/cfd/force

fix ID group-ID nve/cfd_cn/sphere

The fix couple/cfd/force/implicit has been removed and most functionality was moved to the regular couple/cfd/force. To consider the drag in an implicit formulation the integrators fix nve/cfd_cn/* can be used. For more details please read the CFDEMcoupling documentation.