Jul 1 2004
Contents
 
Introduction
Reference Guide
User's guide
 ICM-shell
 ICM graphics
 Structure analysis
 Sequence, searches and alignments
 Energetics and electrostatics
 Manipulations with molecules
 Animation
 Transformations and symmetry
 Maps and factors
  How to manipulate with structure factors
  How to calculate phases of reflections given a 3D model and a cell
  How to automatically place a fragment into density
 How to plot
 How-to: Docking and Virtual Ligand Screening
 Example scripts
References
Glossary
 
Index
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3.9 Maps and factors
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[ structurefactors | cp | dc ]

3.9.1 How to manipulate with structure factors

[Top]
The basic description of structure factors is given in the Glossary.

3.9.2 How to calculate phases of reflections given a 3D model and a cell

[Top]
Basic steps:
  • define crystallographic cell, map gridstep, and resolution (i.e. max h,k and l)
  • build electron density map with the specified parameters
  • calculate structure factors

Example:
 
 read pdb "1igd"                      # use your PDB name here 
 myCell   = Cell(a_1.) 
 gridstep = 0.5 
                                      # map dimensions 
 maxHKL = Iarray(0.45 * myCell[1:3]/gridstep) 
 defSymGroup = 19  # P212121 group 
 make map gridstep 
 make factor maxHKL "mySF" 
 fcalc = Sqrt( mySF.ac * mySF.ac + mySF.bc * mySF.bc ) 
 phase = Atan2(mySF.bc , mySF.ac) 
 group table mySF phase 
 show mySF 

In order to compare calculated phases I would recommend using the same factor table when calculating the _second_ set of phases. Then "ac" and "bc" columns will be simply replaced by the new calculated data, and new "phase2" column would be right next to the "phase" column, relating to the original object. In addition to the previous script:
 
 read pdb "1igd"                      # use your PDB name here 
 myCell   = Cell(a_1.) 
 gridstep = 0.5 
 maxHKL = Iarray(0.45 * myCell[1:3]/gridstep) 
 defSymGroup = 19 # Symgroup("P 21 21 21") 
 make map "myMap" gridstep 
 make factor maxHKL "mySF" 
 phase = Atan2(mySF.bc , mySF.ac) 
                              # ... now the 2nd object ... 
 read pdb "1crn"	      # the second PDB, not 1crn, of course 
 superimpose a_1. a_2.                 
   # you may need an alignment, see superimpose 
 make map "myMap" gridstep myCell     # to have the same cell! 
 make factor maxHKL "mySF" 
 phase2 = Atan2(mySF.bc , mySF.ac) 
 delta = Remainder(phase2-phase , 360.0) 
 group table mySF phase phase2 delta  # maybe something else 
 show mySF 


3.9.3 How to automatically place a fragment into density

[Top]

This section needs to be written. Make maps, set GRID.margin to about the size of the ligand and run montecarlo.


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