> CELL a b c alpha beta gamma
set unit cell constants. If b or c are omitted, the same value as for a is used, if angles are omitted, they are set to 90 degress. Without arguments, the cell constants are listed.
> addauxref qh qk ql
Define the vectors for the scattering plane.
> REF qh qk ql a3 a4 sgl sgu Ei Ef
Make an entry in the list of peaks. For angles and k-values not given, the current motor positions are used. The peak number and the peak data are returned.
> REF AUX qh qk ql Add an auxiliary reflection to the list of reflections. A4 is calculated from the cell constants, the current ei and ef values are used. A3 is left alone or is calculated to have the right angular difference to the previous reflection. Using auxiliary reflections is a help during setup of the instrument or in powder mode.
The sequence:
ref clear all cell aa bb cc alpha beta gamma addauxref ax ay az addauxref bx by bz makeub 1 2with ax, ay, az being the first plane vector and bx, by, bz being the second plane vector creates a UB matrix which allows to drive Q positions and qm. But be aware that a3, sgu and sgl values are still invalid.
> REF CLEAR peak
Remove a peak.
> REF CLEAR ALL
Remove all peaks.
> REF
List all peaks.
> MAKEUB peak1 peak2
Calculate, activate and print out the UB matrix, as well as the peak list with qhkl values calculated back. peak1 is used as the main peak, i.e. driving to the angles given for this peak will correspond to a QHKL which may only differ by a scalar factor of about one, if the cell constants are not correct. peak2 is used only for determining the scattering plane.
It has to be checked that this is fully compatible with the TASMAD specification. In principle, AX,AY,AZ should correspond to peak1 and BX,BY,BZ to peak2.
>MAKEUBFROMCELL
Calculate and activate a UB which has been calculated from the cell constants alone. This is useful to get a4 when no reflection has yet been found to calculate a proper UB.
>MAKEAUXUB qh qk ql
Calculate a UB matrix from the first reflection and an auxiliary second reflection specified through the miller indices qh , qk, ql. The auxiliary reflection will have the same angles as the first reflection, except a3 and a4 will be adjusted to match the requirements from the crystalls geometry.
Markus Zolliker: there should be a an easy way helping the user to correct the cell constants (for example due to thermal contraction) according to the measured peak.
> LISTUB
List the UB matrix, the cell constants and all stored reflections.
This formalism allows to drive out of the scattering plane using the tilt motors of the sample stage. Some cryostats cannot stand this. Therefore driving out of plane can be switched off and on.
> TASUB OUTOFPLANE 1
This command switches out of plane operation on.
> TASUB OUTOFPLANE 0
This command switches out of plane operation off.
> TASUB OUTOFPLANE
lists the current value of the outofplane variable
Example session:
(Some numbers might not be correct, as this module
does not yet work in this form).
We enter cell values
> CELL 2.88 2.88 2.88 90 90 90
> MAKEUBFROMCELL
MAKEUBFROMCELL builds a UB matrix from the cell only. With this you can drive to 2 0 0
> drive qh 2 0 0
This will get you the correct two-theta == a4. You have to search the peak in a3, sgu and sgl and optimize it.
Once we are at the maximum:
> REF 2 0 0
Peak QH QK QL A4 A3 SGL SGU
1 2.00 0.00 0.00 65.31 -87.21 1.25 -5.22
> makeauxub 0 4 4
> dr qh 0 4 4
Make an axiliary UB and drive to the theoretical position for 0 4 4
Find the peak 0 4 4 and optimize it.
...
Once we are at its maximum:
> REF 0 4 4
Peak QH QK QL A4 A3 SGL SGU
1 0.00 4.00 4.00 65.31 -87.21 1.25 -5.22
Show again the peak list:
> REF
Peak QH QK QL A4 A3 SGL SGU
1 2.00 0.00 0.00 65.31 -87.21 1.25 -5.22
2 0.00 4.00 4.00 99.45 20.39 4.25 -1.22
Calculate the UB matrix, with 2 0 0 as primary peak and 0 4 4 as
secondary peak.
> MAKEUB 1 2
UB 2.456 0.530 -0.200
-0.530 2.456 -0.090
0.200 0.090 2.456
Peak QH QK QL A4 A3 SGL SGU QH QK QL
1 A 2.00 0.00 0.00 65.31 -87.21 1.25 -5.22 2.03 0.00 0.00
2 B 0.00 4.00 4.00 99.45 20.39 4.25 -1.22 0.02 3.95 4.03
the last 3 columns above show the Q values calculated back from the angles.
We drive now to the 2 0 0 peak
> DR QH 2 0 0
> PR A4 A3 SGL SGU
A4 = 64.218
A3 = -87.515
SGL = 2.258
SGU = -3.217
The value of A4 has changed, because the cell constants do not match the values
given for the first peak. The value of A3 has changed by the same reason, and
in addition, because the the plane given by 2 0 0 and 0 4 4 is now tilted back
into in the scattering plane. For the latter reason SGU and SGL have changed also.
> DR QH 3 3 3
> PR A4 A3 SGL SGU
A4 = 82.516
A3 = -31.215
SGL = 2.258
SGU = -3.217
note that the values for SGU and SGU have not changed. The will not change
as long as we stay in the scattering plane (no drives to Q3) and as long
as the UB matrix has not changhed.
> REF 3 3 3
Peak QH QK QL A4 A3 SGL SGU
3 3.00 3.00 3.00 82.32 -31.25 2.26 -3.22
> MAKEUB C B
UB 2.456 0.530 -0.200
-0.530 2.456 -0.090
0.200 0.090 2.456
Peak QH QK QL A4 A3 SGL SGU QH QK QL
1 2.00 0.00 0.00 65.31 -87.21 1.25 -5.22 2.03 0.00 0.00
2 B 0.00 4.00 4.00 99.45 20.39 4.25 -1.22 0.02 3.95 4.03
3 A 3.00 3.00 3.00 82.32 -31.25 2.26 -3.22 3.00 3.00 3.00
We have calculated a new UB matrix, based on the peak 3 3 3 as primary and the
0 4 4 as secondary peak. The UB matrix has not changed, as we were already exactly
at 3 3 3.