General Remarks on Crystal Data Cards

Cards which have the same initial letter must be placed sequentially, but cards within a group with the same initial letter may occur in any order. They are usually identified by a CCSL-word of up to 4 characters which follows the initial letter on the card (e.g. CONT , PLOT for Fourier maps or FIX , VARY for Least Squares).

In order to make input more compact, certain cards may (after the initial letter) contain sequences of CCSL-word/number pairs, as on the M card:

M DTYP 4 FTYP 2 SCAL 1000 DELT 0.3

The most common example of this is the I card described below. The facility extends to M , D , G and L cards, but only for those CCSL-words which expect a single number after them.

The first word on some types of card (e.g. A (atom position), F (form/scattering factor) and J (multipole) cards) is an atom-label or scattering-factor-label identifying a particular atom or form-factor. The atom-label or scattering-factor-label may itself be followed by a CCSL-word, as for instance on Q (magnetic structure) and W (wave-function) cards.

Almost all cards fit into the scheme in which the first letter and a following CCSL-word are used for identification, although none of the cards used in the simple example in Chapter 1 does.

The N (name of job) card uses all 79 characters as a title for output; the S (symmetry) cards simply give one symmetry operator each.

The I cards give instructions about the details of a particular run, and may change from run to run, whereas, say, an S card does not. An example is:

I MCOR 80 NCYC 5 CYC1 4

which, when read by a Least Squares Refinement program, says ``for this particular run print only correlations above 80%, and do 5 cycles of refinement, labelling the first 4". The general format is a sequence of CCSL-word/number pairs. The words and numbers may be interpreted in any way the user wishes, so I cards may drive a variety of different main programs depending on how they are interpreted.