Proper and improper NCS

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Proper or closed Non-crystallographic symmetry (NCS) describes a set of NCS operations which form a closed group, for example a set of rotations about an axis. Each operator relates several monomers onto NCS copies. As a result:

  • The self rotation function is strong.
  • An averaging mask may cover a single monomer, or all of the related monomers.

Improper or closed Non-crystallographic symmetry (NCS) describes a set of NCS operations which do not form a closed group, for example a translation. Each operator relates only a simple monomers onto an NCS copy. As a result:

  • The self rotation function is weak.
  • An averaging mask must cover a single monomer only.

Image:NCS-proper-improper.png

--Kevin Cowtan 06:02, 18 April 2008 (CDT)

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