C Cell parameters

ITEMS READ:

C $a, b, c, \alpha, \beta, \gamma$
or
C SD followed by the ESD's in the corresponding parameters on the C card
or
C SD PROD followed by the ESD's in the 6 cell quadratic products

ITEMS DEMANDED:

C , $a$, and any others of $b, c, \alpha, \beta, \gamma$ which are not implied by the space group symmetry (which must have already been set up).

ASSUMPTIONS MADE:

As zero is not a plausible value for either a cell side or an angle, any of the 6 values which is read as zero is deduced from the space group symmetry, assuming that it is either fixed or related to one of the values read previously.

DETAILS:

$a, b$ and $c$ are cell sides in real space, normally in Å, but they need not be. However note that the units must be compatible with units on F cards, $\lambda$ on D cards etc. $\alpha$, $\beta$ and $\gamma$ are the interaxial angles in degrees.

The C SD PROD form should be used when the cell dimensions have been determined from d-spacing values only (eg program DSLSQ) If a C SD line is given without other data, then it will be filled in in the new CDF after a least squares refinement of the unit cell has been made.

NOTE:

Any change of units from Å may lead to implausible default values e.g. for bond lengths used in slack constraints. It will also have consequences on the extinction parameters.

EXAMPLES:

C 5.4560 5.4560 12.6700 90.0 90.0 120.0
C 5.4560 0 12.6700
C 5.4560, 0, 12.6700
C 5.4560,,12.6700

with hexagonal symmetry, are all equivalent. However,

C 5.456 12.67

would not be; this says a=5.4560 and b=12.6700

ROUTINES WHICH READ THE CARDS:

Routine RECIP calls INPUTC to read the C card and then deduces the real and reciprocal cells and transformations. (Routine SETFC also calls RECIP).