When working with molecular models, precise control over the position and orientation of structures is often essential. Whether you’re preparing a system for simulation, building a complex assembly, or analyzing molecular interactions, the ability to move selected components smoothly and intuitively can save both time and frustration.
In SAMSON, a platform for integrative molecular design, this control is provided by move editors — interactive tools that allow you to rotate and translate atoms, molecules, and other objects directly in the viewport. In this post, we’ll take a deeper look at three built-in move editors: the Displacer, the Local Move Editor, and the Global Move Editor. Each of them offers different types of transformations that can be especially useful in different molecular modeling tasks.
Displacer Move Editor
The Displacer is designed for quick manipulation of selected nodes in the plane of the screen. Ideal when working interactively (e.g., adjusting during simulations), it works by dragging the selection directly using the mouse. You can activate it with the shortcut D.
It also supports “snapping” to a grid, which is particularly handy for positioning objects at consistent intervals (e.g., every 0.5 Å). Snapping preferences can be adjusted via the Viewport quick access menu or through Interface → Preferences → Editors → Snapping.
Local Move Editor
For molecular modeling tasks that require more refined control, the Local Move Editor allows you to rotate and translate selected items along their own principal axes. Activate it with the shortcut M.
You can use:
- The central widget (a cross of arrows) to move in the screen plane
- Straight arrows to move along the object’s local axes (X, Y, Z)
- Curved arrows to rotate around those axes
- A trackball widget for free rotation
This level of control is especially helpful when adjusting parts of a molecule while maintaining its internal frame of reference, such as tweaking side chains or rotating fragments to match experimental data.
Even fine features such as dihedral angle rotations are supported simply by clicking on a bond and rotating using the widget that appears:
Global Move Editor
If alignment to a common frame is your goal — for instance, positioning molecules symmetrically in a system — the Global Move Editor helps by aligning manipulations strictly along the global XYZ axes. Activate it with K.
This is particularly useful in constructing molecular assemblies or comparing models across simulations. The widgets are color-coded to match global directions:
- Red: X axis
- Green: Y axis
- Blue: Z axis
Tip: Use Snapping for Precision
Snapping options, available in each move editor, allow you to control how much a structure moves or rotates in each step. For example, use translational snapping for editing crystal structures, or rotational snapping to arrange molecules symmetrically around a pivot point.
This combination of interactive widgets, snapping settings, and shortcut keys gives you full control to position and orient molecular models with clarity and precision.
You can learn more about move editors in the detailed documentation.
SAMSON and all SAMSON Extensions are free for non-commercial use. You can download SAMSON at https://www.samson-connect.net.