vibeqc.write_xyz_trajectory

vibeqc.write_xyz_trajectory(path, frames, comments=None, *, append=False)[source]

Write a sequence of Molecule frames as a multi-XYZ trajectory file.

Parameters:

  • path (str | PathLike) – Output file path.

  • frames (Iterable[vibeqc._vibeqc_core.Molecule]) – Iterable of Molecule objects, one per trajectory frame. All frames should share the same atom count and ordering — most viewers (moltui, ASE, OVITO) assume this so atom-by-atom interpolation makes sense. We don’t enforce it here (you can write a chemistry-changing trajectory like a bond-cleavage if you really want), but a UserWarning is emitted if frame N has a different atom count than frame 1.

  • comments (Sequence[str] | None) – Optional per-frame comment strings (one per frame). The XYZ format puts comments on line 2 of each frame; viewers often display them as labels. Default: numeric "frame N".

  • append (bool) – If True, open in append mode so the new frames extend an existing trajectory file. Default: overwrite.

Returns:

The number of frames written.

Return type:

int

Examples

Geometry-opt animation:

opts = []                                    # collect mols
for it in range(50):
    mol = step(mol, gradient_at(mol))
    opts.append(mol)
vq.write_xyz_trajectory("opt.xyz", opts)

Normal-mode movie (helper below produces the frames for you):

frames = vq.normal_mode_trajectory(mol, hess, mode_index=8)
vq.write_xyz_trajectory("h2o-asym-stretch.xyz", frames)