PLAT021 Type_4 Check Expected number of Reflections (Max = 1 Centro, 2 - non-centro)

The expected number of reflections corresponds to that in the asymmetric unit of the Laue group. Expected ratio: less-or-equal 1 for centro symmetric structures and less than 2 for non-centrosymmetric structures. Reasons to exceed those numbers can be:

1 - Systematic extinctions not omitted from the observed data count.

2 - Refinement with redundant (i.e. not merged/unique) data set.

3 - SHELXL HKLF 5 Refinement.

(http://journals.iucr.org/services/cif/checking/PLAT021.html)

警告原因：針對富余的獨(dú)立衍射點(diǎn)的測試。實(shí)際獨(dú)立衍射點(diǎn)數(shù)在cif文件中_reflns_number_total項給出；期望獨(dú)立衍射點(diǎn)數(shù)相當(dāng)于Laue群中不對稱單元的衍射點(diǎn)的個數(shù)，這個數(shù)值通過晶胞參數(shù)、空間群、theta max算出。對于中心對稱空間群，二者的比應(yīng)小于等于1；對于非中心對稱空間群，二者的比應(yīng)小于2。遠(yuǎn)超過上述數(shù)值會有Alert，產(chǎn)生的原因有：

1. 系統(tǒng)消光的衍射點(diǎn)未被扣除。

2. 使用未被合并的數(shù)據(jù)進(jìn)行精修。

3. 使用HKLF 5格式的數(shù)據(jù)進(jìn)行精修。

解決策略：一般不會出現(xiàn)。如果數(shù)據(jù)未合并需要合并數(shù)據(jù)。

PLAT022 Type_3 Check Expected number of Reflections (completeness)

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.

(http://journals.iucr.org/services/cif/checking/PLAT022.html)

警告原因：該項為針對缺少衍射點(diǎn)的測試。當(dāng)實(shí)際獨(dú)立衍射點(diǎn)遠(yuǎn)小于期望值時，會給出Alert。產(chǎn)生的原因有使用面探檢查器收集數(shù)據(jù)缺失或者倒易空間收集錯誤。

解決策略：重新還原數(shù)據(jù)或者重新收集數(shù)據(jù)。

PLAT023 Type_3 Check Theta-Max

Check resolution of the data set. Alert is issued when sin(theta)/lambda < 0.6

(http://journals.iucr.org/services/cif/checking/PLAT023.html)

警告原因：檢查數(shù)據(jù)分辨率。當(dāng)sin(theta)/lambda < 0.6時表明數(shù)據(jù)分辨率低。

解決策略：重新還原數(shù)據(jù)或者重新收集數(shù)據(jù)。

PLAT024 Type_4 Check for required Friedel pair averaging Z<=Si (Obsolete 1/1/2011)

(No longer imposed)

(http://journals.iucr.org/services/cif/checking/PLAT024.html)

Averaging of Friedel pairs is advised when indicated by a large s.u. on the Flack parameter. Large s.u. values indicate that the anomalous scattering power is too small in combination with the data quality at hand to merit refinement with a non-averaged data set. This will generally be the case with MoKa data sets for structures containing atoms not heavier than Si. The value of the Flack parameter will be largely meaningless anyway for large s.u. values. Use MERG 3 or MERG 4 in case of refinement with the SHELXL97 program. Non-compliance with the above for valid scientific reasons should be discussed in detail in the experimental section of the paper.

例：PLAT024_ALERT_4_B Merging of Friedel Pairs is STRONGLY Indicated

警告原因：當(dāng)Flack系數(shù)的誤差較大時，表明反常散射能力弱。一般與體系中沒有重原子有關(guān)。可以將Friedel對合并進(jìn)行精修。

解決策略：一般不會出現(xiàn)。使用MERG 3或者M(jìn)ERG 4合并Friedel對重新精修即可。

PLAT025 Type_1 Check for Hmin..Lmax

Check reported h,k,l - range with calculated range based on reported theta-max.

(http://journals.iucr.org/services/cif/checking/PLAT025.html)

警告原因：報道的hkl范圍和計算得到的hkl范圍不一致。

解決策略：一般不會出現(xiàn)。精修重新生成CIF文件即可。

PLAT026 Type_3 Check for a weak data set

Check whether a sufficient fraction of the unique data set is indeed above the 2 * sigma(I) level.

All reflection data are included in this test. Check whether this low ratio is caused by weak data beyond sin(theta)/lambda > 0.5 (i.e. low resolution).

(http://journals.iucr.org/services/cif/checking/PLAT026.html)

例：PLAT026_ALERT_3_C Ratio Observed / Unique Reflections too Low ....47 Perc.

警告原因：獨(dú)立衍射點(diǎn)中可觀測獨(dú)立衍射點(diǎn)比例低。

解決策略：可以嘗試用SHEL 999 0.84命令或OMIT -2 50命令截去一部分高角度點(diǎn)，如果不行就只能重新收數(shù)據(jù)了。

PLAT027 Type_3 Check _diffrn_reflns_theta_full

Ideally (and a requirement for publication in Acta Crystallographica), the dataset should be essentially complete, as defined by -diffrn-measured-fraction-theta-full (close to 1.0), up to sin(theta)/lambda = 0.6 (i.e. 25.24 degrees MoKa).

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 image processing 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.

(http://journals.iucr.org/services/cif/checking/PLAT027.html)

警告原因：當(dāng)數(shù)據(jù)完整度接近1，theta角應(yīng)滿足sin(theta)/lambda大于等于0.6時，小于0.6時會給出Alert。數(shù)據(jù)完整度低的原因主要有：

數(shù)據(jù)收集策略時探測器只圍繞主軸線轉(zhuǎn)動，可以重新把晶體放置在載晶臺上補(bǔ)充數(shù)據(jù)。

數(shù)據(jù)處理時強(qiáng)點(diǎn)由于無法處理被排除，可以減少曝光時間減弱衍射強(qiáng)度。

掃描不完整。

解決策略：可以嘗試用SHEL 999 0.84命令或OMIT -2 50命令截去一部分高角度點(diǎn)，如果不行需調(diào)整曝光時間重新收集數(shù)據(jù)。

PLAT028 Type_3 Check the reported _diffrn_measured_fraction_theta_max

Ideally, the reported '_diffrn_measured_fraction_theta_max' value, corresponding to theta-max, should be close to 1.0.

(http://journals.iucr.org/services/cif/checking/PLAT028.html)

警告原因：theta-max角度下數(shù)據(jù)點(diǎn)部分缺失。

解決策略：使用SHEL或OMIT命令適當(dāng)截去少量高角度點(diǎn)即可。

PLAT029 Type_3 Check the reported _diffrn_measured_fraction_theta_full

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 image processing 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. (See SHELXL manual). PLATON may be used to analyse the case at hand (by invoking either the 'FCF-VALIDATION' mode or the 'ASYM-VIEW' mode).

(http://journals.iucr.org/services/cif/checking/PLAT029.html)

例：PLAT029_ALERT_3_A _diffrn_measured_fraction_theta_full Low ....... 0.93

警告原因：當(dāng)theta-full滿足sin(theta/lambda)大于等于0.6時，數(shù)據(jù)完整度低。原因同PLAT027相同。

解決策略：可以嘗試用shel 999 0.84或omit 0 50或omit -3 50切去一部分高角度點(diǎn)，如果不行需調(diào)整曝光時間重新收集數(shù)據(jù)。

PLAT030 Type_1 Check _diffrn_reflns_number >= reflns_number_total

The number of measured reflections should be equal or greater than the number of unique reflections.

(http://journals.iucr.org/services/cif/checking/PLAT030.html)

警告原因：收集衍射點(diǎn)數(shù)應(yīng)大于等于獨(dú)立衍射點(diǎn)數(shù)。

解決策略：一般不會出現(xiàn)，重新精修生成CIF文件即可。