When a molecular project contains several conformations, finding the one you need can become a small but persistent source of friction. Names may be similar, and browsing candidates one at a time makes it harder to narrow the search. If the conformations differ in size, their atom counts offer a simple first filter.
In SAMSON, the Node Specification Language (NSL) lets you describe nodes with expressions. The conformation attribute space matches conformation nodes, and its short name is co. For atom-count searches, the relevant attribute is numberOfAtoms, abbreviated nat.
Find conformations above a size threshold
To match conformations with more than 100 atoms, use:
co.nat > 100
The full attribute-space form is conformation.nat > 100. This is useful when you want to narrow a set by a clear numerical criterion before inspecting candidates further. For example, a modeler comparing conformations of different sizes can use an atom-count threshold as an initial sorting question: “Which candidates are larger than this?”
Focus on a range
If you have a target size range in mind, specify it directly:
co.nat 100:200
This matches conformations with a number of atoms between 100 and 200. The equivalent long form is conformation.nat 100:200. A range can be more useful than a single cutoff when a project contains both very small and very large structures, but your next step concerns only candidates of an intermediate size.
These expressions are filters, not explanations of why two conformations differ. Atom count alone does not tell you whether a conformation is biologically relevant, structurally similar, or suitable for a particular calculation. Treat it as a practical way to reduce the candidate set—not as a substitute for evaluating the structures themselves.
Use names and selection state as additional clues
The conformation attribute space inherits several attributes from the general node space. You can refer to a conformation’s name with co.n, for example co.n "A" or co.n "L*". You can also test whether a conformation is selected with co.selected, or whether it is not selected with not co.selected. The inherited selection flag is available as co.sf; examples include co.sf false and co.sf.
These attributes provide useful ways to express what you are looking for: a name, an atom-count criterion, or a selection state. For instance, you might first identify candidates in a size range and then use names or selection state to distinguish items in your workflow. The examples here show individual expressions; consult the NSL reference for the language’s broader syntax and additional examples rather than assuming how separate conditions should be combined.
A small habit that saves time
Before manually inspecting a long list, ask whether a simple property can reduce it. For conformations, atom count is an easy-to-state criterion: use co.nat > 100 for a threshold or co.nat 100:200 for a range. Keep the expression short, check that it represents the question you actually have, and then inspect the resulting structures in context.
For attribute definitions and more examples, see the SAMSON conformation attributes reference.
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