When a project contains many conformations, it is easy to lose time opening them one by one just to find the ones with a particular atom count. A quick filter can narrow the search before you inspect structures in detail. In SAMSON, the Node Specification Language (NSL) provides a dedicated attribute for this: conformation.numberOfAtoms, abbreviated co.nat.
Start with the question you need to answer
Maybe you want to locate conformations with more than 100 atoms, or focus on those whose atom counts fall in a particular range. Rather than relying on names or manually checking each conformation, express the criterion directly:
co.nat > 100matches conformations with more than 100 atoms.co.nat 100:200matches conformations with a number of atoms between 100 and 200.
The full attribute name works too: conformation.nat > 100. The short form is simply more compact when you use the attribute repeatedly.
Why filter by atom count?
Atom count is a straightforward way to divide a set of conformations into groups you can examine separately. For example, a range can help you isolate a subset of interest when the full set contains conformations of different sizes. A threshold can help you identify which conformations meet a minimum or maximum size criterion. The filter does not tell you whether a conformation is scientifically appropriate; it gives you a precise, repeatable way to find candidates for your next inspection.
This is useful whenever the task is “show me the conformations with this many atoms,” rather than “show me the conformation with this name.” It also makes the criterion visible as an expression, so you can review what you searched for instead of relying on memory.
Keep the attribute space in mind
The co prefix refers to the conformation attribute space, which matches only conformation nodes. That scope matters: an expression beginning with co is not a general atom-count query for every kind of node. If a search returns fewer results than expected, first check whether the items you want to match are represented as conformations.
Conformations also inherit some attributes from the general node attribute space. You can refer to their names with co.n, for example co.n "A" or co.n "L*". They also support co.selected and its negation, not co.selected. The inherited selectionFlag attribute has the short form co.sf, with examples including co.sf and co.sf false. The selected attribute has no short name in this attribute space.
A small, reusable search habit
Before browsing a large collection, write down the property that would make a conformation worth inspecting. If that property is atom count, turn it into a co.nat expression and use either a threshold or a range. Then treat the matching conformations as a shortlist—not as a verdict on quality. This separates the mechanical task of finding candidates from the scientific task of deciding what to do with them.
For the complete attribute reference and additional examples, see the SAMSON conformation attributes documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.