How to Minimize Only a Part of a Molecule in SAMSON.

Minimizing molecular structures is a fundamental task in molecular modeling. But what if you're dealing with a large molecule and only need to optimize part of it without affecting the rest? SAMSON, the integrative molecular design platform, provides an intuitive way to achieve this. Here, we’ll explore how to minimize just a part of a molecule using SAMSON's interactive tools.

The Challenge: Selective Minimization

In molecular studies, you often encounter situations where working with a small region within a larger structure is necessary. Minimizing the entire molecule every time can be computationally heavy, inefficient, and unnecessary. Instead, focusing on a specific part while keeping the rest untouched can save time and resources. SAMSON offers a simple process to perform this kind of selective minimization.

The Solution: Freezing Atoms Outside the Zone of Interest

The selective minimization technique in SAMSON involves temporarily freezing atoms to lock their positions. Follow these steps to minimize a specific part of a molecule:

  1. Select the whole molecule or leave the selection empty, depending on your preference. This can be done intuitively within SAMSON by referencing the Selecting guide.
  2. Freeze the atoms and regions you don't want to minimize. Click Edit > Freeze or use the keyboard shortcut F. The frozen atoms will appear with a dark blue overlay in the viewport for easy identification.
  3. Select the region to minimize. For instance, you could target a functional group in a molecule or specific atoms within a larger structure by using SAMSON’s flexible selection tools.
  4. Start the minimization. Use Edit > Minimize, or simply press Z, to begin interactive minimization of the selected region. The frozen atoms outside the selection will remain fixed, giving you detailed control over the desired part of the structure.
  5. Once completed, unfreeze the entire system if required, so the molecule is restored to full flexibility. This can be done by selecting the frozen parts (or leaving the selection empty) and clicking Edit > Unfreeze or pressing U.

Example: Visualizing Frozen Atoms

As you work, SAMSON visually highlights the frozen atoms with a dark blue overlay, making it easier to distinguish between the minimized and untouched regions. Take a look:

The interactive minimization preferences

Notes and Tips

Note

When a part of a molecule is minimized, the minimizer considers the entire connected component that includes the selected atoms. For instance, selecting a single atom within a molecule means the whole connected structure containing that atom will be minimized. If you wish to refine only part of a connected component, the freezing method is essential.

Selective minimization is an excellent approach for local optimizations. It allows molecular modelers to focus computational resources where they are needed most, without unnecessary recalculations for the rest of the molecule. This process is especially useful when dealing with large biomolecules, complexes, or systems under active design scenarios.

Interested in learning more about minimization in SAMSON? Discover the full guide in the interactive minimization documentation.

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

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