Probably bad contacts. Put this repel sequence just before your 'proper'
Powell.
parameter nbonds repel=0.9 rcon=4 end end
minin powell
nstep 40
drop=40
end
parameter nbonds repel=0.0 rcon=4 end end
If it persists increase the value of repel cautiously.
Jim
--
James Raftery
Structural Chemistry Department|E-Mail:jrtest at spec.ch.man.ac.uk
Manchester University | FAX:0161-275-4734
Manchester M13 9PL | Tel.:0161-275-4700