[mcstas-users] Ordering of reflections in single crystal hkl file

[Coates, Leighton]

Hi All

After rerunning several simulations with McStas last week I think we (me and Franz Gallmeier)  stumbled on something relating to simulating diffraction from
Large molecules (lots of reflections)  from what we can tell it makes a big difference how the input hkl file is ordered for the single
Crystal component.

We are thinking that the Single crystal component searches through the text file of Bragg reflexes and terminates when 2*wavevector < Tau,
because then the Bragg condition cannot be satisfied at any angle.

However if the Bragg reflexes are ordered from high to low Tau or not ordered well this happens much faster than if the list of reflexes is ordered from low Tau to high Tau.

Thus to make things work properly the hkl file should be ordered from low to high Tau. Has anyone seen this before and Peter does this make sense or is it something else?

I checked out  the example file  YBaCuO.lau (see below) from the example data and it looks formatted that way. The Crystallographica program cannot handle large molecules so its not possible
To use it I guess we are using the single crystal component for things  it was never designed to handle !


YBaCuO: cubic
2    # a=b=3.8186, c=11.6777; 90 deg
3    #
4    # Format parameters: Crystallographica format
5    # column_j  4 multiplicity 'j'
6    # column_d  5 d-spacing 'd' in [Angs]
7    # column_F2 7 norm of scattering factor |F|^2 in [fm^2]
8    # column_h 1
9    # column_k 2
10    # column_l 3
11    #
12    # h   k   l Mult. d-space 2Theta   F-squared
13      0   0   1   2  11.6777  7.57041  76.2348
14      0   0  -1   2  11.6777  7.57041  76.2348
15      0   0   2   2  5.83885  15.1741  397.027
16      0   0  -2   2  5.83885  15.1741  397.027
17      0   0   3   2  3.89257  22.8458  2084.26
18      0   0  -3   2  3.89257  22.8458  2084.26
19      0   1   0   2   3.8843   22.895  2310.15
20      0  -1   0   2   3.8843   22.895  2310.15
21      1   0   0   2   3.8186  23.2944  1590.25
22     -1   0   0   2   3.8186  23.2944  1590.25
23      0   1  -1   4  3.68575  24.1465  79.9977
24      0  -1   1   4  3.68575  24.1465  79.9977
25      0   1   1   4  3.68575  24.1465  79.9976
26      0  -1  -1   4  3.68575  24.1465  79.9976
27      1   0   1   4  3.62948  24.5266  21.5105
28      1   0  -1   4  3.62948  24.5266  21.5105
29     -1   0   1   4  3.62948  24.5266  21.5105
30     -1   0  -1   4  3.62948  24.5266  21.5105
31      0   1   2   4  3.23404  27.5814   891.25
32      0  -1  -2   4  3.23404  27.5814   891.25
33      0   1  -2   4  3.23404  27.5814   891.25
34      0  -1   2   4  3.23404  27.5814   891.25
35      1   0  -2   4  3.19583  27.9179  1402.22
36     -1   0   2   4  3.19583  27.9179  1402.22
37      1   0   2   4  3.19583  27.9179  1402.22
38     -1   0  -2   4  3.19583  27.9179  1402.22
39      0   1   3   4  2.74953   32.566  20895.5
40      0  -1  -3   4  2.74953   32.566  20895.5
41      0   1  -3   4  2.74953   32.566  20895.5
42      0  -1   3   4  2.74953   32.566  20895.5
43      1   0   3   4  2.72593  32.8559  22705.3
44      1   0  -3   4  2.72593  32.8559  22705.3
45     -1   0   3   4  2.72593  32.8559  22705.3
46     -1   0  -3   4  2.72593  32.8559  22705.3
47      1   1   0   4  2.72309  32.8911  22369.7
48      1  -1   0   4  2.72309  32.8911  22369.7
49     -1   1   0   4  2.72309  32.8911  22369.7
50     -1  -1   0   4  2.72309  32.8911  22369.7
51      1  -1  -1   8  2.65194  33.7997   265.48
52     -1   1   1   8  2.65194  33.7997   265.48
53      1   1   1   8  2.65194  33.7997   265.48
54      1   1  -1   8  2.65194  33.7997   265.48
55     -1  -1   1   8  2.65194  33.7997   265.48
56     -1  -1  -1   8  2.65194  33.7997   265.48
57      1  -1   1   8  2.65194  33.7997  265.479
58     -1   1  -1   8  2.65194  33.7997  265.479


Best Wishes

Leighton