Freezing Atoms for Partial Molecular Minimization in SAMSON

Molecular modelers often encounter a common challenge: how can you optimize specific regions of a molecule without affecting the rest of its structure? This is especially relevant when working on large molecules where only a local part of the system needs refinement or adjustment. If this sounds familiar, you may find SAMSON’s ability to freeze atoms for partial molecular minimization highly practical.

Why Freeze Atoms?

Freezing atoms during minimization allows you to optimize only the necessary region of a molecule. Using this feature, you can focus specifically on a subset of atoms (such as an active pocket or a distorted part) while keeping the remaining structure intact. This targeted approach keeps broader molecular features preserved and saves computational resources.

How to Minimize a Part of a Molecule in SAMSON

With SAMSON, minimizing a part of a molecule involves a structured workflow. Here’s how you can do it:

  1. Select the molecule. Start by selecting the entire molecule you want to work on, or simply keep the selection empty.
  2. Freeze unwanted atoms. Use the Edit > Freeze option to fix the positions of either the selected atoms or, if nothing is selected, the entire molecule. Freezing locks these atoms, ensuring they are excluded from minimization.
  3. Select the region to optimize. Next, select the specific subset of atoms that you want to optimize. These will now be unaffected by the frozen portions of the molecule.
  4. Unfreeze the target region. Use Edit > Unfreeze to unlock just the selected atoms for optimization while the rest stays fixed.
  5. Perform the minimization. Initiate the minimization process by selecting Edit > Minimize to start an interactive exploration of the minimized structure.
  6. Finalize the adjustments. Once satisfied, stop the minimization with another click of Edit > Minimize. To return the molecule to its fully flexible state, ensure the whole molecule is selected or unselected and click Edit > Unfreeze.

Additional Insights

Freezing atoms not only aids precision but also gives immediate visual feedback. In SAMSON’s viewport, frozen atoms are overlaid with a dark blue color, helping you track which parts of the molecule remain fixed. Thanks to this visual cue, you can confirm your molecular setup is accurate before committing to minimization.

Here is an example from SAMSON, illustrating how frozen atoms appear in the interface:

The interactive minimization preferences

A Visual Example: Video Guide

For a more dynamic demonstration, SAMSON provides an excellent video walking users through the process of minimization with frozen atoms. You can find it embedded directly within the documentation to see this workflow in action.

Conclusion

This feature is a game-changer for anyone who needs to focus on specific regions of a molecule during geometry optimization. By utilizing freezing and selective minimization, SAMSON makes localized adjustments easy, precise, and effective. To learn more about how to perform these operations, visit the original documentation page: https://documentation.samson-connect.net/users/latest/minimizing/.

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

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