James Holton wrote:
Perhaps the best way to settle this is to put it out to a challenge:
does anybody have a map calculated with an average
FOM(fromsomeprogram) < 0.5 that they were able to trace?
I saw ARP/wARP iteratively tracing such densities if the resolution was
1.5 A or higher - a bit subjective answer, I suspect.
If the resolution is 1.0 A or higher then ab-initio or semi-ab-initio
programs (e.g. ACORN) can recover a structure from a value of FOM close
to zero - again, only iteratively.
Does anyone have a map calculated with FOM(fromsomeprogram) > 0.5 that
was total garbage?
Yes, a lot. Two simple examples are:
Type 1: lack of strong low angle reflections (e.g. due to overloads).
Even for a FOM value approaching 1.0 the map would hardly be
interpretable. More general case is the data having bad Wilson plot.
Type 2: pathological cases with 60 degrees phase error (FOM 0.5) to each
of the two enantiomorphs, left and right-hand MIR solutions, similar SAD
cases (60 degrees to the correct phases and 60 degrees to those for the
'babinet-sign-inverted' map).
Victor
