D Diffraction information

A D card starts with D then a CCSL-word which determines what else is on the card. There is no predetermined sequence for D cards, although it is desirable to type all D cards starting with the same CCSL-word consecutively.

DATA FOLLOWING ALLOWED CCSL WORDS:

GEOM
Data

An integer IGEOM defining the diffraction geometry.
Values of IGEOM allowed are:

1

Normal beam with Zone-axis vertical

2

Equatorial 3-circle with Zone-axis vertical

3

Equi-inclination

4

Precession

5

Anti-equi-inclination

6

4-circle bisecting geometry

7

4-circle general geometry, angles to be given

8

Normal beam general geometry

9

Powder data

10

Powder data, X-ray

11

4-circle diffractometer, high-chi geometry

12

SXD geometry

WVLN
Data

The wavelength(s) in the same units as the lattice constants.

UMAT
Data

The 9 elements of the UB-Matrix relating the crystallographic axes to the diffractometer axes thus:

$X$

is parallel to the incident beam at omega=0,

$Z$

is parallel to the omega axis,

$Y$

makes up an orthogonal right handed set.

Reference:

Busing and Levy Acta Cryst 22 p247, but note the different definition of the diffractometer axes and the transposition of the matrix.

TH2M
Data

2$\theta$ for the monochromator in degrees (needed for X-ray polarisation corrections).

L/R
Data

+ve if the incident beam is diffracted to the right.
$-$ve if the incident beam is diffracted to the left.
value 1 for angles measured clockwise about $+$ve diffractometer axes, or 2 for anticlockwise.

ROTA
Data

The zone-axis which is parallel to the rotation axis for IGEOM = 1,2,3,4,5.

CHIA
Data

Three integers and a real number. For IGEOM = 2 the real number is the angle in degrees between the normal to the Chi circle and the direction of the reciprocal space vector whose indices are the 3 integers.

ANGP
Data

The precession angle in degrees for IGEOM = 4.

CARDS DEMANDED:

GEOM and either UMAT or ROTA with possibly CHIA or ANGP

TELESCOPING OF SIMPLE CARDS:

The GEOM, TH2M, L/R and ANGP information may occur together.

EXAMPLE:

D WVLN 0.9190
D GEOM 8
D L/R 1
D UMAT 0.20457 -0.00747 -0.01437
D UMAT 0.00894 0.20391 0.02125
D UMAT 0.01989 -0.03210 0.29975
or

D L/R -2 GEOM 11

ROUTINES WHICH READ THE CARDS:

Routine SETDC calls INPUTD to read the D cards and then sets up the diffraction geometry. SETABS, SETLP and SETPOL all call SETDC.