March 11, 1996
Again PC-GSAS has undergone extensive revision to both
fix bugs and provide several
important enhancements. Only PC-GSAS has been updated at
this time. Allen Larson and
I are working to port these enhancements and fixes to
the other versions. We expect
new VMS versions to appear next followed by the unix
ones. The following are some of
the major fixed and enhancements:
1. The space group bug which gave incorrect extinctions
for some cubic space groups
has been fixed.
2. The GSAS menu system had had a number of bugs fixed
and it has been improved as well.
It now checks to see that an experiment name has been
declared before running those
things that need it (i.e. EXPEDT). It now includes items
for file conversion (CNVFILE),
a better DOS interface and DLST to delete the list file.
3. The graphics now draw lines on a white background so
that images can easily be cut
and pasted into other windows.
4. Both the mouse and arrow keys work to position the
cursor. ALT- accelerates the
cursor.
5. The bug in DISAGL that sometimes gave incorrect esd's
for distances & angles for
large numbers of atoms has been fixed.
6. Many small (& I'm sure annoying) errors in EXPEDT
have been fixed. I want to thank
all those who pointed them out to me, it really helps.
7. The error in PUBTABLES that reported gamma=90 for
certain hexagonal space groups
has been fixed.
8. GEOMETRY has been modified so that more of its output
for rigid body fitting and
hydrogen atom placement appears in the list file. It's
possible to input data strings
by cut & paste between a window with the list file open
via an editor and the GSAS
window running EXPEDT.
9. The peak asymmetry function of Finger, Cox & Jephcoat
for CW data has been installed
as function #3 for both x-ray and neutron data. This
needs extensive testing beyond
what I have been able to do with data in hand. The two
asymmetry parameters ('S/L' &
'D/L') are very highly correlated, so you may have to
fix one & refine the other.
10. Peak shape functions #1 & #3 for TOF data have been
extended to include effects
due to macroscopic strain and more general microstrain
effects.
11. GSAS now handles energy dispersive x-ray powder
diffraction data but only in the leBail
mode.
12. GSAS now contains the generalized spherical
harmonics description for texture for both
TOF and CW data. It can be used in place of the
March-Dollase model for Bragg-Brentano data.
Select "cylindrical symmetry" for the sample (default)
and choose some order for the
harmonics. The texture code will handle other cases as
well. However, we have not been able
to implement the spherical harmonics for the tetragonal
space groups (P m3, etc.) We hope to
add this as soon as we work out the extremely extensive
table of Fourier coeffcients needed
for this. Contact me for details.
13. The graphics now supports HP-GL and color PostScript
hardcopy.
14. REFLIST now has an option for producing a file with
h,k,l and Fo for a selected phase
suitable for input into a direct methods program
(MULTAN, etc.). Please let me know if you
want other info. on this file as well.
15. The output or the correlation matrix by GENLES has
been changed to be more compact and
readable. Only terms greater than 75% are listed.
As you can see, I have done a lot of development in the
PC version of GSAS. One reason for this
is the apparent extreme interest in this version. Some
80% of all requests from you for GSAS
distribution kits are for the PC version. I expect this
trend to continue for the forseeable
future. Running times for fast PC's (100MHz and above)
are very competitive with workstations
and multiple GSAS runs can be done simultaneously with
sufficient memory and Win95.
Again, I thank all who have provided ideas for
improvements and bug reports. Keep them coming.
Bob Von Dreele