Molecular modelers often face the challenge of refining specific sections of large molecular structures without affecting the rest of the system. This can be crucial when working on localized optimizations, focusing computational resources, or preserving specific regions of a molecule for subsequent analysis. Thankfully, SAMSON’s interactive minimization features come equipped with a well-designed solution: the ability to minimize only a part of a molecule using the freeze and unfreeze functionality.
In this blog post, we’ll explore how to selectively minimize parts of a molecule in SAMSON while keeping the rest of the structure intact. This feature is incredibly useful for handling larger systems where not every atom needs to be optimized or shifted.
Freezing and Minimizing a Section of a Molecule
The freeze functionality in SAMSON lets you lock parts of a molecule to prevent them from being affected during minimization. Here’s a step-by-step explanation to refine only the desired parts:
- Select the entire molecule or leave the selection empty if you want to freeze the entire structure.
- Navigate to Edit > Freeze. This will lock the atoms in your selection (or in the entire document if nothing is selected).
- Now, make a new selection of the specific part of the molecule you want to minimize. This can be as precise as desired, down to individual atoms or bonds.
- Unfreeze the selected atoms by clicking Edit > Unfreeze. Only these atoms will now be active and subject to optimization.
- Start the minimization process by selecting Edit > Minimize. The active (unfrozen) atoms will adjust their positions while the frozen atoms stay fixed in place.
Once you’re satisfied with the results, you can unfreeze the system as needed. Simply select the entirety of the molecule again or leave the selection blank, then click Edit > Unfreeze.
Key Tips to Remember
- The frozen regions are marked visually with a dark blue overlay in the SAMSON viewport. This makes it easy to identify which parts of the structure remain fixed.
- When minimizing a selected part, SAMSON considers the entire connected component of the selection. For instance, selecting a single atom will include the entire molecule connected to that atom in the minimization process. To minimize only part of a connected component, use the freeze functionality extensively to isolate specific atoms or bonds.
Below is an illustrative example. Observe how SAMSON uses freezing to control which atoms are optimized during interactive minimization.
Why Use Partial Minimization?
Partial minimization provides tremendous flexibility when working with molecular structures. It allows you to:
- Focus optimizations only on regions of interest, saving both time and computational power.
- Preserve specific regions of a molecule, which might be experimentally validated or need stability during the workflow.
- Easily explore variations or conformational changes in specific sub-structures without having to isolate them in a separate document.
Instead of applying global adjustments, this nuanced approach ensures your modeling workflow stays efficient and targeted.
To learn more about minimizing molecular structures in SAMSON, refer to the full documentation here: https://documentation.samson-connect.net/users/latest/minimizing/.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get started today at https://www.samson-connect.net.