R-factor：
It is usually the sum of the absolute difference between observed (Fo) and calculated (Fc) over the sum of the observed.
It is also possible to lower the R-factor by deleting observed data and by raising the number of parameters.
well-refined structures have R-factors below 20–25 percent.
Free R-factor：
If refinement is progressing correctly, the free R-factor will drop as well.the free R-factor is generally below 30 percent.
Root-mean-square (r.m.s.) deviations should not be much larger than 0.02Å for bond lengths, and 3° for bond angles.
φ,ψ plot：
main-chain dihedral angles： φ （空间二面角）
if more than a few percent of all the residues have φ,ψ values completely outside allowed regions, one should suspect errors.
Nonstandard Stereochemistry：
Solvent Structure：
winson-B:
是假设每个原子的b因子都一样， 所应该得到的结构的b因子的数值。是一种衍射强度的性质。因为wilson B在计算时会忽略结构中最高的b因子， 所以wilson-b一般会小于average-b。
mosaicity：
In crystallography, mosaicity is a measure of the spread of crystal plane orientations. A mosaic crystal is an idealized model of an imperfect crystal, imagined to consist of numerous small perfect crystals (crystallites) that are to some extent randomly misoriented. Empirically, mosaicities can be determined by measuring rocking curves.
Asymmetric Unit
The asymmetric unit is the smallest portion of a crystal structure to which symmetry operations can be applied in order to generate the complete unit cell (the crystal repeating unit). Symmetry operations most common to crystals of biological macromolecules are rotations, translations and screw axes (combinations of rotation and translation).
biological assembly
The biological assembly (also sometimes referred to as the biological unit) is the macromolecular assembly that has either been shown to be or is believed to be the functional form of the molecule.
单晶和孪晶
晶向
occupancy
Rmerge
分辨率函数的指标 Rmerge=|I (k)-I|/I (k)
Patterson function
POLARRFN
Matthews Coeff
The Matthews number is usually between 1.66+ and 4.0+ corresponding to protein contents of 75% to 30% but proteins with higher solvent contents will give higher values.
P(reso) is the probability using the input high resolution limit and P(tot) is the probability across all resolution ranges
反常散射
晶体衍射中弗里德耳定律，不论晶体中是否存在对称中心,在晶体衍射中总存在着对称中心,即FHKL=FHKL。但是当使用的X射线波长与待测样品中某一元素的吸收边靠近时,就不遵从上述定律,也即FHKL≠FHKL。这是由电子的反常散射造成的,利用这一现象可以解决待测物的相角问题。
Scherrer公式
可根据谱线变宽的量估算晶粒在该衍射方向上的厚度
B-factor：
温度值（也称为温度系数或B系数）是用来表示原子的热稳定性的一个温度因子。可以应用于每个原子（或原子组）的因子，它描述了电子密度的弥散程度。原子会在自己的位置上震动。因为在连续晶胞中的同一原子会处于不同的震动位置，他们所展示的x－ray衍射所表示的原子的大小其实是大于原子本身的大小的。B因子与原子的均方位移（U）的平方成正比；随着U增加，B因子也增加，原子对散射的贡献减小了。如果原子在模型中的位置不正确，则它们的B因子将高于附近正确放置的原子。所以在计算原子位置时需要换算上一个热力参数b，也就是b因子。结构越不稳定，震动越强烈，这个原子的b因子也就越高。而average-b则是整个分子的平均b因子。温度因子还跟晶体数据的分辨率有关，如果分辨率越差，蛋白整体温度因子越高，坐标误差也越大。
