Precisely positioning atoms and molecules is a frequent task in molecular modeling software. Whether you’re assembling a structure, inspecting conformations, or preparing a simulation, the ability to control how parts of your model move can make a big difference.
In SAMSON, the move editors provide intuitive ways to translate and rotate molecular components with flexibility and control. In this post, we’ll focus on the Local Move Editor, a handy tool for manipulating parts of your model along their principal axes.
Why use the Local Move Editor?
It often happens that you want to rotate just one portion of your molecule around its own axis—say, tweaking a dihedral angle—or move a fragment without disturbing the rest. The Local Move Editor lets you:
- Translate parts of molecules along directions that make sense within that part’s geometry
- Rotate around logical internal axes
- Snap translations and rotations to defined intervals
- Access fine controls through context menus
How it works
To get started, open or load a molecule in SAMSON. Use the rectangle selection editor to select the group of atoms you want to move. Then, activate the Local Move Editor by pressing M.
You’ll see a widget appear over the selection:
- The center cross with arrows handles translations in the camera plane.
- The straight arrows represent translations along the local X, Y, and Z axes.
- The curved arrows allow for axis-based rotations.
- A trackball enables free 3D rotation.
Translating in the camera plane
Click and drag on the central cross to move the selection within the plane of your current view:
Snapping movement and rotations
For accurate adjustments, consider enabling snapping. This aligns movements or rotations to fixed increments. Snapping options can be found in the top-left of the viewport or via Edit > Preferences > Editors.
Rotating on demand
Use the curved arrows to rotate around local axes. Snapping helps in making neat 10° or 15° turns:
Trackball rotations
Use the spherical widget to rotate freely in 3D. This is useful when you need orientation changes without worrying about staying aligned to specific axes.
Use cases
The Local Move Editor shines when you’re adjusting molecular conformations, refining structure layouts before simulation, or arranging multiple fragments spatially. Coupled with snapping, it can help replicate symmetry and create uniform arrangements with minimal effort.
Want to go further?
The Local Move Editor is one of several tools available in SAMSON for controlling motion. If you need global transformations or want to align structures using reference frames, SAMSON has dedicated editors for that too. See the full documentation on Moving Objects to explore further.
SAMSON and all SAMSON Extensions are free for non-commercial use. To get SAMSON, visit https://www.samson-connect.net.