GeoConstraints

This page gives hints on how to constaint the geometry of the system in geometry optimization, molecular dynamics or searches with the ABINIT package.

Introduction¶

There are two mechanisms to put constraints on the atom positions in ABINIT. They can be used in geometry optimization, molecular dynamics (including PIMD) or other geometry algorithms (e.g. transition path searches).

The simplest one (entry point iatfix) simply define a set of atoms that are fixed, either entirely, or only along one of the directions (for the latter, see the warning in iatfix)

A more complex one, but also much more powerful, allows to place constraints on linear combinations of atomic positions. Thanks to such constraint, the mean position of two atoms (or a fragment, like a molecule) can be fixed, or constrained to stay within an arbitrary plane. One can thus also sample different mean positions. See a complete description in wtatcon.

basic:

• iatfix Indices of AToms that are FIXed
• iatfixx Indices of AToms that are FIXed along the X direction
• iatfixy Indices of AToms that are FIXed along the Y direction
• iatfixz Indices of AToms that are FIXed along the Z direction
• natfix Number of Atoms that are FIXed
• natfixx Number of Atoms that are FIXed along the X direction
• natfixy Number of Atoms that are FIXed along the Y direction
• natfixz Number of Atoms that are FIXed along the Z direction

useful:

• iatcon Indices of AToms in CONstraint equations
• natcon Number of AToms in CONstraint equations
• nconeq Number of CONstraint EQuations
• wtatcon WeighTs for AToms in CONstraint equations

Selected Input Files¶

No input file associated to this topic.