Constrained relaxation and dynamics

[andrea-angeletti]

How can I perform structure optimisation and molecular dynamics by constraining the cell shape? In VASP it would be equivalent to ISIF=8 or what you can achieve with ICONST, which allows you to relax the lattice parameters without changing the angle between primitive vectors.

[BowenD-UCB]

This is currently not implemented.
And I looked into ase.filters and ase.constraints, seems there is no support for this neither.

The easist way to implement this is to force the stress tensor to be diagonal before passing to a structural optimization.

Can you please test this and make a pull request if it works well?

[janosh]

There is FixSymmetry. Never used it myself but maybe that does what you want.

[janosh]

Oh and also FixInternals.

Allows fixing bonds, angles, dihedrals as well as linear combinations of bonds (bondcombos).

[BowenD-UCB]

@janosh I suppose FixSymmetry also fix the atoms to be on high-symmetry points

[janosh]

Based on doc str, you can control angle fixing and atom fixing separately.