Density modification

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[edit] Traditional density modification

Phase improvement by density modification involves the alternate application of two processes:

  • Map modification: We modify the electron density in accordance with

chemical knowledge about the nature of protein structures. This gives rise to a modified map.

  • Phase combination: We weight the modified phases on the basis of

how well the modified magnitudes match to their observed values, and then perform a weighted combination with the experimental phases. This part of the calculation is performed in reciprocal space.

Fourier transforms are required in calculating the initial map from the current phase estimates, and calculating modified structure factors from the modified map.

Software which implements traditional density modification includes:

  • dm
  • solomon
  • CNS

[edit] Statistical density modification

Software which implements statistical density modification includes:

  • RESOLVE
  • pirate

--Kevin Cowtan 06:04, 18 April 2008 (CDT)

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