PROC-NAME: DIFMN02 Type_2

PURPOSE: To check that _refine_diff_density_min is within expected limits.

PROCEDURE:

DMIN = _refine_diff_density_min

DTEST = 0.1 * ZMAX

TEST

IF DMIN < -DTEST*2 issue ALERT A

? ? ? ? ?"Alert A The minimum difference density is < -0.1*ZMAX*2.00"

< -DTEST issue ALERT B

? ? ? ?? "Alert B The minimum difference density is < -0.1*ZMAX*1.00"

< -DTEST*.75 issue ALERT C

? ? ? ?? "Alert C The minimum difference density is < -0.1*ZMAX*0.75"

? ? ? ? The minimum residual electron density is more negative than normally expected, even after making an allowance for the heaviest element in the structure. This is often an indication that (a) the absorption corrections are inadequate; (b) the overall quality of the data may be poor, leading to spurious peaks and holes of residual electron density; (c) there is twinning which has not been allowed for where overlap from the second twin domain (which may have been ignored in the data collection) causes errors in the intensities of some reflections; (d) the model is incorrect or incomplete in terms of incorrect element assignment, missing atoms or unmodelled or inadequately modelled disorder or solvent atoms.

? ? ? ? If you believe you have eliminated all potential causes of this alert, but the minimum residual electron density still remains more negative than normally expected, you must specify the name of the nearest atom to this minimum and its distance from the minimum.

IF DMIN > 0.0 issue ALERT A

? ? ? ?? "Alert A The minimum difference density is > 0.0"

? ? ? ? The minimum residual electron density should have a negative value. Have you forgotten the sign or reversed the minimum and maximum entries?

(http://journals.iucr.org/services/cif/checking/DIFMN_02.html)

目的：PURPOSE: 檢查_refine_diff_density_min是否在預期范圍內。

過程：

DMIN = _refine_diff_density_min

DTEST = 0.1 * ZMAX

檢查

若DMIN小于-DTEST*2，則發(fā)布A級警告

? ? ? ?? "Alert A The minimum difference density is < -0.1*ZMAX*2.00"

若DMIN小于-DTEST，則發(fā)布B級警告

? ? ? ?? "Alert B The minimum difference density is < -0.1*ZMAX*1.00"

若DMIN小于-DTEST*.75，則發(fā)布C級警告

? ? ? ?? "Alert C The minimum difference density is < -0.1*ZMAX*0.75"

? ? ? ? 即使考慮到結構中最重的元素，最小殘余電子密度峰也比正常預期值更負。這通常表明：(a) 吸收校正不充分；(b)數(shù)據(jù)的整體質量可能較差，導致出現(xiàn)虛假的殘余電子密度峰(鬼峰)和殘余電子密度空穴；(c)由于第二孿晶組分(在數(shù)據(jù)收集中可能已被忽略)的重疊引起某些衍射點的強度出現(xiàn)錯誤而導致不被允許的孿晶；(d)由于元素指認錯誤、原子缺失或未建?；驘o序處理不充分或溶劑原子導致的模型不正確或不完整。

? ? ? ? 若你認為你已經消除了導致此警告的所有潛在原因，但最小殘余電子密度峰仍然比預期值更負，則必須給出最接近此最小殘余電子密度峰的原子的名稱及它們之間的距離。

若DMIN大于0.0則發(fā)布A級警告

? ? ? ?? "Alert A The minimum difference density is > 0.0"

? ? ? ? 最小殘余電子密度應為負值。檢查是否忘記負號或將最小和最大值填反了。

例：DIFMN02_ALERT_2_B The minimum difference density is < -0.1*ZMAX*1.00

_refine_diff_density_min given = -6.968

Test value = -5.300

警告原因：最小殘余電子密度值超出預期范圍。

解決策略：按上述藍色中文內容檢查數(shù)據(jù)和結構，進行相應改正即可。

關于該警告的一個具體解釋例子參考下面鏈接中的公眾號文章：

https://mp.weixin.qq.com/s/irYbkyXuk1kRluJryBZYeg