When a molecular project contains several conformations, finding the one you need can become a small but persistent distraction. Maybe you want to narrow the list to larger conformations, or focus on candidates within a particular size range. In SAMSON, the Node Specification Language (NSL) provides a direct way to describe that search using the conformation’s number of atoms.
The key attribute is numberOfAtoms, abbreviated nat. Its full form is conformation.numberOfAtoms; the short form is co.nat. Because the conformation attribute space matches conformation nodes, these expressions are intended to find conformations based on their atom counts.
Make the first pass by size
To find conformations with more than 100 atoms, use:
co.nat > 100
This is useful when you already know that very small conformations are not relevant to the task at hand. The expression gives you a clear threshold to adjust: change 100 to the count that makes sense for your search.
If you are looking for conformations around a particular size rather than above a threshold, use a range:
co.nat 100:200
The documentation describes this as matching conformations with a number of atoms between 100 and 200. You can also write the longer version, conformation.nat 100:200. The short and long forms express the same attribute, so choose whichever is easier to read in your working context.
Read the expression carefully
It is easy to confuse the attribute name with an example value. The relevant attribute is nat, not n: co.nat 100:200 filters by atom count, while co.n refers to the inherited name attribute. In the summary table, one example appears as co.n 100:200, but the detailed description identifies the atom-count range expression as co.nat 100:200. For filtering by number of atoms, use co.nat.
This distinction is especially helpful when building queries from memory. A quick check of the attribute’s meaning can prevent a name-based expression from being mistaken for a numeric count filter.
Other useful conformation attributes
Conformations also inherit several attributes from the general node attribute space. You can refer to a conformation’s name with co.n, using a quoted string, as in co.n "A". The documentation also shows co.n "L*" as an example. Selection status is available through co.selected or not co.selected. The inherited selection flag can be written as co.sf or co.sf false.
These attributes answer different questions: co.nat describes how many atoms a conformation has, while name and selection attributes describe other properties. Keeping that distinction in mind makes it easier to choose an expression that reflects the actual search you want to perform.
A practical way to use the filter
Start with the question you need answered: are you looking for conformations above a minimum size, or within a size interval? Use co.nat > 100 for the first kind of threshold, or co.nat 100:200 for the documented range form. Then adjust the numbers to suit your search. This turns an open-ended scan into a more focused query without requiring you to remember the full attribute name.
For the complete attribute reference and additional examples, see the SAMSON conformation attributes documentation.
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