[pdDMG] A definition for F_meas_squared for powder data

[Robert Von Dreele]

Good
On 3/21/2017 5:43 PM, James Hester wrote:
> A further refinement to the definition based on feedback:
>
> ;
>      The structure factor amplitude for the reflection derived by 
> partitioning
>      the background-subtracted observed intensity 
> _pd_proc.intensity_net between
>      reflections in the same proportion as those reflections contribute to
>      the corresponding background-free calculated point in 
> _pd_calc.intensity_net .
>
> ;
>
>
> On 21 March 2017 at 16:37, James Hester <jamesrhester at gmail.com 
> <mailto:jamesrhester at gmail.com>> wrote:
>
>     Examination of the GSAS-II GetFobsSq routine suggests that a more
>     precise definition would note that the background should be
>     subtracted first.   I propose the following revised definition:
>
>     ;
>          The structure factor amplitude for the reflection derived
>     from a powder
>          histogram by partitioning observed intensity between peaks at
>     each point
>          in the same proportion as the model peaks contribute to that
>     point.
>          Model background is subtracted from both observed and
>     calculated values
>          before partitioning.
>     ;
>
>     On 13 March 2017 at 15:43, James Hester <jamesrhester at gmail.com
>     <mailto:jamesrhester at gmail.com>> wrote:
>
>         Dear Powder Dictionary Management Group,
>
>         It is now recognised formally that CIF dictionaries may need
>         to redefine datanames, and DDLm has been equipped with some
>         facilities to handle this.  In the case of the DDLm version of
>         the powder dictionary, as far as I can tell the only two
>         datanames from the core that are implicitly different are
>         refln.F_complex and refln.F_meas_squared.  _refln.F_complex is
>         different purely because the phase id has to be considered
>         when performing the calculation (unlike in the core case).
>         _refln.F_meas_squared is different both because of the need to
>         consider phase_id, but also because the procedure for
>         calculating f_meas_squared from the powder histogram is
>         completely different to the single crystal case.  Could you
>         all please consider what I have written below for
>         F_meas_squared, and suggest any improvements. Ideally, the
>         definition text should be clear enough for a programmer to
>         implement the calculation.
>
>         While I would appreciate feedback from at least some of you,
>         if I don't hear from you within a week or so, I will assume
>         that the definition below is adequate.
>
>         all the best,
>         James.
>
>
>         (New cif_pow definitions follow)
>
>         save_refln.F_complex
>
>         _definition.id <http://definition.id> '_refln.F_complex'
>         loop_
>           _alias.definition_id
>                  '_refln.F_complex'
>                  '_refln_F_complex'
>         _definition.update 2017-03-07
>         _description.text
>         ;
>              The structure factor vector for the reflection calculated
>         from
>              the atom site data for the phase given by phase_id.
>         ;
>         _name.category_id refln
>         _name.object_id F_complex
>         _type.purpose Measurand
>         _type.source Derived
>         _type.container Single
>         _type.contents Complex
>         _enumeration.default 0.
>         loop_
>           _method.purpose
>           _method.expression
>                  Definition
>         ;
>                  If (_diffrn_radiation.probe == "neutron") 
>         _units.code =  "femtometres"
>             Else If (_diffrn_radiation.probe == "electron")
>         _units.code =  "volts"
>             Else _units.code =  "electrons"
>         ;
>
>         save_
>
>         save_refln.F_squared_meas
>
>         _definition.id <http://definition.id> '_refln.F_squared_meas'
>         loop_
>           _alias.definition_id
>                  '_refln.F_meas'
>                  '_refln_F_meas'
>         _definition.update 2017-03-07
>         _description.text
>         ;
>              The structure factor amplitude for the reflection derived
>         from a powder
>              histogram by partitioning observed intensity between
>         peaks at each point
>              in the same proportion as the model peaks contribute to
>         that point.
>         ;
>         _name.category_id refln
>         _name.object_id F_squared_meas
>         _type.purpose Measurand
>         _type.source Derived
>         _type.container Single
>         _type.contents Real
>         _enumeration.default 0.
>         loop_
>           _method.purpose
>           _method.expression
>                  Definition
>         ;
>                  If (_diffrn_radiation.probe == "neutron") 
>         _units.code =  "femtometres"
>             Else If (_diffrn_radiation.probe == "electron")
>         _units.code =  "volts"
>             Else _units.code =  "electrons"
>         ;
>
>         save_
>
>         -- 
>         T +61 (02) 9717 9907 <tel:+61%202%209717%209907>
>         F +61 (02) 9717 3145 <tel:+61%202%209717%203145>
>         M +61 (04) 0249 4148
>
>
>
>
>     -- 
>     T +61 (02) 9717 9907 <tel:+61%202%209717%209907>
>     F +61 (02) 9717 3145 <tel:+61%202%209717%203145>
>     M +61 (04) 0249 4148
>
>
>
>
> -- 
> T +61 (02) 9717 9907
> F +61 (02) 9717 3145
> M +61 (04) 0249 4148
>
>
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