24小时热门版块排行榜

返回列表

qhy12

铁虫 (小有名气)

应助: 3 (幼儿园)
金币: 1099.1
散金: 29
帖子: 166
在线: 74.4小时
虫号: 587931
注册: 2008-08-22
专业: chemistry

[交流] 【请教】如何解决cif表中的两个A级错误和一个B级错误

PLAT022_ALERT_3_A Ratio Unique / Expected Reflections too Low ....    0.51

Test for data completeness. The ratio of the reported number of unique
reflections and expected number of reflections for the resolution given is
reported. The ratio can be low due to a missing cusp of data when collected
with a 2D-detector. Alternatively, the wrong asymmetric part of reciprocal
space was collected on a serial detector system.

PLAT029_ALERT_3_A _diffrn_measured_fraction_theta_full Low .......    0.54

Ideally (and a requirement for publication in Acta Crystallographica),
this fraction should be close to 1.0 for theta-full greater or equal
to sin(theta/lambda) = 0.6 (i.e. 25.24 degrees for MoKa and 67.7 degrees
for CuKa  radiation).
The three major causes of incomplete data sets are:
1 - A missing cusp of data due to data collection by rotation around
   the spindle axis only (standard on some image-plate systems).
   Cure: collect an additional data set after remounting the crystal.
2 - The DENZO imageprocessing package has problems with certain strong
   reflections. They are often excluded from the data set.
   Cure: Add an additional scan at lower power setting in order to
   include strong low order reflections.
3 - Incomplete scans, possibly based on erroneously assumed higher than
   actual symmetry.
Note: The default value of _diffrn_measured_fraction_theta_full that
is automatically calculated and inserted in the CIF by SHELXL-97 might
generate A-level ALERTS when significant numbers of reflections are
missing at higher theta values. In order to avoid such an ALERT,
substitute the values calculated with the SHELXL instruction 'ACTA 50'
for _diffrn_reflns_theta_full and _diffrn_measured_fraction_theta_full
respectively. For Mo-radiation, corresponding values of 25 degees (or
higher) and 0.99 (or higher) are expected.
PLATON may be used to analyse the case at hand (by invoking either the
'FCF-VALIDATION' mode or the 'ASYM-VIEW' mode).

[font=黑体]PLAT088_ALERT_3_B Poor Data / Parameter Ratio ....................    7.82

The data/parameter ratio should in general be higher than 10 for a quality
structure determination. This ratio can be improved by not refining
C-H parameters other than riding on their carrier atom.

加入acta 50也不能解决，说是用'ASYM-VIEW' ，不知如何用？

[ Last edited by qhy12 on 2010-9-15 at 17:38 ]

回复此楼