When a molecular project contains many conformations, finding the right one to inspect can become a small but persistent source of friction. Names may be inconsistent, and browsing a long list is not always the quickest way to narrow the field. If the question is simply “Which conformations contain more than a certain number of atoms?”, SAMSON’s Node Specification Language (NSL) provides a direct filter.
Search by size, not by guesswork
Conformation-specific attributes live in the conformation attribute space, abbreviated co. Its numberOfAtoms attribute has the short name nat and accepts integer values. To match conformations containing more than 100 atoms, use:
co.nat > 100
The full attribute-space form is conformation.nat > 100. Both expressions refer to the number of atoms in a conformation; the shorter one is handy when writing a query repeatedly.
You can also specify a range:
co.nat 100:200
This matches conformations with an atom count between 100 and 200. The documentation describes the range as “between” those values, so if inclusion of the endpoints matters for your task, check the behavior in your SAMSON query context rather than assuming it from the notation.
Keep the attribute names straight
A useful detail: co.nat is the atom-count attribute, while co.n is the name attribute. The documentation’s attribute table includes an example that appears to pair co.n with a numeric range, but the detailed examples identify the range query as co.nat 100:200. For filtering by atom count, use nat, not n.
This distinction matters because the two attributes answer different questions. A name query such as co.n "A" refers to a conformation’s name; an atom-count query such as co.nat > 100 refers to its size. The documentation also shows a quoted name pattern, co.n "L*". Use the name attribute when you are looking for a label, and the atom-count attribute when you are narrowing by the number of atoms.
Use selection attributes deliberately
Conformations also inherit the selected and selectionFlag attributes from the general node attribute space. For example, co.selected and not co.selected express whether a conformation is selected, while co.sf and co.sf false refer to its selection flag. The conformation-specific documentation does not define the broader behavior of these inherited attributes, so consult the node reference if you need to understand their exact role.
A practical way to narrow the search
Start with a concrete question: do you need conformations above a size threshold, or within a particular size interval? Write the corresponding co.nat expression, then use a name or selection attribute only when that is relevant to your search. Keeping each condition tied to the right attribute makes queries easier to read and reduces the risk of filtering on a label when you meant to filter on atom count.
Atom count is a useful way to organize or narrow a set of conformations, but it does not by itself say whether a conformation is scientifically suitable. Treat it as a size filter, then assess the resulting structures using the criteria appropriate to your modeling task.
For the full attribute list and syntax examples, see the SAMSON conformation attributes reference.
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