I ran a MacroModel job with constraints, but it failed. The error message contains "TORS attempts to rotate fixed/frozen atoms". Why might this have happened?

The reason for this error is that torsion rotations have been applied to fixed or frozen atoms. This can happen when combining the default setting of Perform Automatic setup during calculation with atom constraints in the Constraints tab.

There are two workarounds:

• Recommended: Use the default Perform Automatic setup during calculation option, but use the Substructure tab to define the fixed and freely moving atoms. These two features work together to detect the available torsion rotations for the conformation search. The freely moving atoms need to be defined as the substructure. All remaining atoms need to be placed into a shell as fixed or frozen.


• Use the Perform Automatic Setup button, and remove torsions in the set of constained atoms.
  
  
  1. Define the atoms to be constrained in the Constraints tab.
  2. In the CSearch tab, clear the Multi-ligand and Perform Automatic setup during calculation options.
  3. Click the Perform Automatic Setup button.
  4. Under Search Variables, select Torsion Rotations and click "Edit.
  5. Remove any torsions (purple bars) that lie within the set of constrained atoms.
  6. Start the search.

Keywords: MacroModel, constraints, automatic setup

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