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There are two kinds of dual-space partial-model extensions which involve the direct-method program OASIS. The first kind, named SAD/SIR iteration, uses SAD/SIR information, while the second kind, named molecular replacement (MR) iteration, does not use that information. In general, the SAD/SIR iteration is more powerful since more experimental information is used. However, in most cases when protein structures are solved with the molecular replacement method, SAD/SIR information is not available. Thus the MR iteration is particularly useful for the completion of models from molecular replacement. The SAD/SIR iteration will be automatically used in OASIS for data sets containing SAD/SIR signals, while the MR iteration will be dedicated to data sets without SAD/SIR signals. The present paper shows that for data containing SAD/SIR signals, a combination of SAD/SIR iteration and MR iteration could lead to significantly better results than that obtained from the SAD/SIR iteration alone. 相似文献
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新矿物丁道衡矿的晶体结构 总被引：2，自引：1，他引：2
对产于内蒙白云鄂博晶态富Ti和Fe2+的硅钛铈矿族新矿物丁道衡矿Ce4Fe2+(Ti,Fe2+)2Ti2Si4O22进行了晶体结构的精测,求得晶胞参数:a=1.34656(15)nm,b=0.57356(6)nm,c=1.10977(12)nm,β=100.636(2)°,晶胞体积V=0.84239(16)nm3。单位晶胞中的分子数Z=2。晶体结构测定中分别用P21/a和C2/m空间群来进行晶体结构解析,解析表明,两种结构模型最终得到的R因子分别为0.026和0.021。两种结构精修后的原子坐标、键长键角都完全合理。根据结构分析及衍射数据消光规律统计认为,丁道衡矿的空间群应该为P21/a,而C2/m为赝对称空间群,结构属于具有C2/m赝对称的P21/a超结构,是一种超结构的新类型。 相似文献
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一维非公度调制结构安康矿X射线衍射及四维空间指标化研究 总被引：1，自引：0，他引：1
采用最新的CCD单晶衍射仪,对一维非公度调制结构矿物安康矿进行了单晶和粉晶X射线衍射研究,利用单晶X射线衍射和三维超结构分析方法测定晶胞参数a=1.014 08(10)nm,b=1.014 08(10)nm,c=0.295 72(6)nm,α=90,°=β90,°γ=90,°调制向量q=0.444c*,据此对单晶衍射数据进行了四维空间的指标化。并用新近研究开发的利用单晶体来进行粉晶衍射的新方法对粉晶衍射实验及粉晶数据的四维空间进行指标化研究。 相似文献
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