Selective Molecular Minimization: A Step-by-Step Guide

Molecular modelers often face the challenge of optimizing specific parts of a molecule or selecting a single molecule from a complex system for minimization. Performing a targeted molecular minimization allows researchers to refine specific sections of their models without affecting the rest of the system. In this post, we’ll guide you through the process of minimizing a single molecule or a selected part of a molecule in SAMSON, providing control and efficiency in optimizing molecular structures.

Why Focus on Selective Minimization?

In molecular modeling, it’s not always necessary—and sometimes not desirable—to minimize the entire molecular system. Selective minimization is particularly useful when analyzing or modifying one molecule within a multi-molecular system, or when refining a specific region of a molecule while leaving the rest of the structure intact. Properly applying these techniques can save computational resources while providing detailed local optimizations.

Minimizing a Single Molecule

To minimize a single molecule (or connected component) without affecting others in the system, you can follow these steps in SAMSON:

Open the Preferences panel and navigate to Interface > Preferences > Editors > Minimize.
Uncheck the option labeled Include all atoms in the document. This ensures that the minimization focuses only on your selected molecule.
Select the specific molecule you wish to minimize.
Click on Edit > Minimize (or use the shortcut Z) to initiate the minimization process.

During this process, the minimizer automatically considers the entire connected component of your selection. This means that if you select one atom from a molecule, the entire molecule connected to that atom will be minimized. If you want to focus on a smaller region, you might need to refine the selection further by freezing parts of the molecule.

Minimizing a Part of a Molecule

Minimizing only a part of a molecule requires freezing specific sections to keep them fixed. The steps below explain how to do this:

Select the entire molecule or leave the selection empty to freeze the whole system.
Click Edit > Freeze to freeze the selected atoms or the entire system if nothing is selected. This ensures these parts remain fixed during minimization.
Next, select only the part of the molecule that you wish to minimize.
Unfreeze the selected atoms by clicking Edit > Unfreeze.
Finally, click Edit > Minimize (or press Z) to start the minimization of the selected region.
When finished, turn off freezing by selecting the entire molecule (or leaving the selection empty) and clicking Edit > Unfreeze again.

Frozen atoms are not minimized, and their positions stay fixed. In the SAMSON viewport, frozen atoms are visually marked with a dark blue overlay to provide clear differentiation.

Example Visualization

The image below shows the interactive minimization preferences in SAMSON where you can configure options to fine-tune your process. These settings give you the flexibility to minimize your structures according to specific needs:

Learn More

The ability to conduct selective molecular minimization is an essential skill for molecular modelers, helping to streamline workflows and improve accuracy. To further explore these features and learn how to apply them to your projects, visit the full documentation page here: https://documentation.samson-connect.net/users/latest/minimizing/

SAMSON and all SAMSON Extensions are free for non-commercial use. You can download SAMSON at https://www.samson-connect.net.