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小木虫2007

[交流] Checkcif发现两个B级错误,帮忙!

Alert level B
PLAT230_ALERT_2_B Hirshfeld Test Diff for    C5     -   C6      ..       8.34 su   
PLAT242_ALERT_2_B Check Low       Ueq as Compared to Neighbors for         C2

[ Last edited by 小木虫2007 on 2007-9-13 at 19:13 ]
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douvei

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小木虫2007(金币+2,VIP+0):谢谢指点!
PLAT230_ALERT_2_B Hirshfeld Test Diff for    C5     -   C6      ..       8.34 su

从下面的解释,可能是您相邻原子各项异性参数相差很大,个人意见是对同一个环或附近同种元素的原子使用simu, delu两个命令,可能会好一些
  The components of the anisotropic displacement parameters along chemical
bonds are assumed to be equal in magnitude. Large differences supposedly
indicate contamination of these parameters with other (unresolved) effects
such as (substitutional) disorder, model or data errors and/or
over-refinement. Atomic sites assigned the wrong scattering type (e.g. Ag
versus Br) should generate 'problem signals' with this test. Data sets
corrected for absorption effects with DELREF techniques (e.g. DIFABS, SHELXA,
XABS2) often show large DELU values for bonds involving the heaviest atom.
Note: The original 'Hirshfeld-test' was defined in absolute terms (see
F.L.Hirsfeld, Acta Cryst. (1976). A32, 239-244). The current test is with
reference to the associated standard uncertainty.

[ Last edited by douvei on 2007-9-11 at 16:41 ]
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2楼2007-09-11 16:37:14
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douvei

金虫 (正式写手)

★ ★
小木虫2007(金币+2,VIP+0):谢谢指点!
PLAT242_ALERT_2_B Check Low       Ueq as Compared to Neighbors for         C2
这种问题可能有两种原因:
(1)原子类型定错了,这种错误很容易纠正
(2)没有无序的原子与无序或者应该处理成无序的原子相连,就会显得原子的ADP很小。如果处理不好,可以用下面的话去解释:
C2 has a smaller adp than the other atoms in the disordered XXX group
because it is bonded directly to CXX, which is not disordered, and thus
has less freedom of movement.
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3楼2007-09-11 16:52:53
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