Dear all,
First of all just "hello" to everyone since I am new to this forum. Not
being a crystallographer, bear with me if I say something crazy.
I was recently tinkering with Sfall and noticed that the Fcalc output by
Sfall have different values depending on if one feeds Sfall with an
input mtz file containing Fobs ("mode sfcalc xyzin" vs. "mode sfcalc
xyzin hklin") and also depending on if one tells Sfall to scale the Fobs
or not ("noscale" on or off). This puzzles me as I would have thought
that since Fcalc are calculated from the atomic coordinates, they should
be affected by neither the Fobs fed to Sfall nor the scaling of the Fobs.
As an example, Sfall calculations on PDB:1AHO. In each case the Fcalc
column is the penultimate one. Here the difference in Fcalc between
scaling or not scaling the Fobs is not so pronounced, but it still
puzzles me that there would be any change at all. Also, in this case
when the Sfall is run without hklin, there is a substantial change in PHIC.
1. HKLIN was provided and scaling turned on.
LIST OF REFLECTIONS
===================
H K L FP SIGFP FC PHIC
0 1 2 162.32 3.86 238.41 270.00
0 1 4 97.72 2.34 190.32 90.00
0 1 5 230.11 12.78 256.90 270.00
0 1 6 205.83 7.00 322.93 90.00
0 2 2 53.28 2.14 198.16 0.00
0 2 4 137.66 5.46 2.63 0.00
0 2 5 249.32 5.84 293.85 0.00
0 2 6 203.96 5.37 303.16 180.00
2. HKLIN was provided but scaling was turned off.
LIST OF REFLECTIONS
===================
H K L FP SIGFP FC PHIC
0 1 2 158.53 3.77 238.28 270.00
0 1 4 95.44 2.29 189.92 90.00
0 1 5 224.74 12.48 256.07 270.00
0 1 6 201.02 6.84 321.43 90.00
0 2 2 52.04 2.09 198.01 0.00
0 2 4 134.45 5.33 2.63 0.00
0 2 5 243.50 5.70 292.83 0.00
0 2 6 199.20 5.24 301.69 180.00
3. HKLIN with Fobs was not provided (both FC and PHIC are quite different)
LIST OF REFLECTIONS
===================
H K L FC PHIC
0 1 2 260.16 -108.18
0 1 4 122.43 -7.47
0 1 5 38.13 81.93
0 1 6 209.85 125.96
0 2 2 386.47 -78.65
0 2 4 145.47 -82.02
0 2 5 107.70 -15.80
0 2 6 101.94 138.75
If anyone could explain, I'd be very grateful. Thanks!
Pawel Janowski
