ESD Syntax in CIF Files

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ESD Syntax in CIF Files

Postby mtconleyuk » Wed Sep 26, 2012 11:33 am

We have recently noted CIF files which specify ESD using the following syntax:
_cell_length_a 6.502+2
_cell_length_b 6.466+2
_cell_length_c 6.481+2

My understanding, from examining the spec, is that ESD values should be specified within parentheses, as in

_cell_length_a 6.502(2)
_cell_length_b 6.466(2)
_cell_length_c 6.481(2)

Yet, when a file containing the '+' notation is passed through the iUCR CheckCIF facility at <>, no warnings at all are generated regarding invalid numeric fields. Also, the '+' formatted data were obtained from the ICSD via RETRIEVE. Is the '+' notation somehow supported? Or is CheckCIF interpreting the data in some other way?
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Re: ESD Syntax in CIF Files

Postby Brian McMahon » Wed Sep 26, 2012 3:18 pm

Definitely not a legitimate way to express standard uncertainties in CIF, though we're rather embarrassed that checkCIF doesn't flag that as a specific error, and shall look into what can be done to remedy that.

Brian McMahon
Research and Development Officer
International Union of Crystallography
5 Abbey Square, Chester CH1 2HU, England (e-mail:
Brian McMahon
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