SEAMM Extract Clusters Plug-in

A SEAMM plug-in for extracting molecular clusters (trimers, tetramers, … larger n-mers) from a condensed-phase, typically periodic, configuration as unwrapped, non-periodic structures – e.g. many-body training data and diagnostics for machine-learned force fields.

• Free software: BSD-3-Clause

• Documentation: https://molssi-seamm.github.io/extract_clusters_step/index.html

• Code: https://github.com/molssi-seamm/extract_clusters_step

History

2026.9.18.1 – Extract from many structures in one step

• The step now takes the standard SEAMM structure selection: the current configuration (the default, as before), all or the last or first configurations of the current system, of all systems, or of systems chosen by name, or a variable holding a list of configurations. Selecting all the configurations of a system that holds a trajectory extracts from every frame in one step, with no loop, and puts all the clusters in one system. Each frame’s clusters are prefixed with its configuration name; clusters.csv and summary.json record the frame; the report aggregates over frames and lists the count per frame. One random stream covers the whole run, so the printed seed reproduces it.

• Requires seamm 2026.9.18.1 and molsystem 2026.9.17.2 or later.

2026.9.18 – Reproducible seeds and motif selection

• The random seed actually used is now always printed and recorded in a new summary.json in the step directory (with the source, bin edges and counts by motif), so a run made with the seed set to “random” can be reproduced by entering the printed value.

• A new “Restrict to motifs” option accepts only clusters with the given contact-graph topology, e.g. ring or ring, star. The dialog offers the motifs the requested cluster sizes can produce. Candidates rejected for their motif are counted and reported, since rare motifs use up the attempt budget.

2026.9.17.1 – Bugfix: a structure without bonds gave clusters of atoms

• Molecules are identified from the bonds, so a configuration read from a format that carries no connectivity (extended XYZ without bond perception) was treated as one atom per molecule and the “clusters” were silently groups of atoms. The step now stops with a clear error pointing at the Read Structure “Perceive bonds” option. Configurations made only of noble-gas atoms or monatomic ions, which legitimately have no bonds, are still accepted.

2026.9.17 – Initial release of the Extract Clusters step

• Extracts n-molecule clusters (trimers, tetramers, … larger n-mers) from the current, typically periodic, condensed-phase configuration as unwrapped, centred, non-periodic configurations in a new system, e.g. many-body training data and diagnostics for machine-learned force fields.

• Clusters are connected subgraphs of a molecular contact graph (molecules are in contact if their contact atoms are within a cutoff, minimum image), so chains, rings and stars all occur; several sizes can be extracted from one frame.

• Optional stratification so the set is flat in the radius of gyration or the largest centroid separation, with bin edges from equal quantiles of a pilot sample or given explicitly, and optional balancing over the contact-graph motif.

• Provenance on every cluster: unique names <frame>_<seed>_<molecules> and #ExtractClusters#scan properties (size, spread, motif, contacts, bin, source molecules) that survive SDF/extxyz export, plus a clusters.csv per step.