When modeling complex molecular systems, precise manipulation of structures is key. Whether you’re arranging ligands, adjusting dihedrals, or preparing a visual output, simple grab-and-drag operations often aren’t enough. Many modelers struggle with getting molecules to move exactly how they want—often needing rotations around a specific axis, translations confined to a particular plane, or snapping for precision placement.
If you’ve ever tried to rotate a part of a molecule just a few degrees without affecting the rest, or had to realign a molecular fragment along its principal axes, the Local Move Editor in SAMSON might be exactly what you need.
What is the Local Move Editor?
The Local Move Editor allows you to translate and rotate selected molecular parts based on their own geometry, rather than the global reference frame. This is especially useful in structural refinement, conformational changes, and visual setup.
Shortcut key: M
Widgets Designed for Control
The interface provides:
- Central translation widget – move objects within the camera plane.
- Axis translation widgets – guided movement along the structural axes of your selection.
- Plane translation widgets – movement constrained to planes defined by principal axes.
- Curved arrows – rotate around the selection’s own X, Y, or Z axes.
- Trackball widget – free 3D rotation in all directions.
Precision Built-In
Moving atoms by eye isn’t always sufficient, especially when fine-tuning interactions or preparing simulations. You can right-click on any widget or use Ctrl / Cmd+Left Click to numerically define translation and rotation values.
What About Snapping?
You can enable snapping for both translation and rotation. For instance, set translational steps to 0.5 Å and rotation to 10°, ensuring that your edits maintain alignment or symmetry. Enable this behavior directly from the quick access menu at the top-left corner of the viewport or via Interface > Preferences > Editors > Snapping.
Snapping becomes especially useful when building structures using repetitive geometric transformations, like aligning atoms on a grid or positioning fragments with rotation symmetry.
Bonus: Editing Dihedrals
The Local Move Editor also supports direct interaction to edit dihedral angles. Just click on a bond and rotate the corresponding molecular fragment.
Undo Is Your Safety Net
One underrated feature: all movements are undoable. Try something out, and if it doesn’t work as planned, just hit Edit > Undo.
When Should You Use the Local Move Editor?
- To position elements with respect to a reference fragment (e.g., docking outcomes).
- To shift or rotate atomic groups during structure preparation.
- To adjust angles without switching toolsets or writing scripts.
- To precisely snap molecules into place when creating design patterns.
If you’re still relying on less precise manipulation tools or external editors, exploring the Local Move Editor could save time and improve structural accuracy.
To learn more about moving objects in SAMSON, visit the official documentation.
SAMSON and all SAMSON Extensions are free for non-commercial use. You can get SAMSON here.