晶胞Unit cell

计算晶胞中原子数时：顶点原子被 8 个晶胞共享（计 1/8），棱上原子被 4 个共享（计 1/4），面心原子被 2 个共享（计 1/2），体内原子完全属于该晶胞。例如简单立方含 1 个原子，体心立方 2 个，面心立方 4 个。晶体密度 ρ = Z·M / (N_A·V)，Z 为晶胞内的化学式单位数。原胞只含一个阵点，而惯用晶胞为了体现对称性可能含多个阵点。

When counting atoms in a cell, a corner atom is shared by 8 cells (counts 1/8), an edge atom by 4 (1/4), a face atom by 2 (1/2), and an interior atom belongs wholly to the cell. Simple cubic thus has 1 atom per cell, body-centred cubic 2 and face-centred cubic 4. Density ρ = Z·M / (N_A·V), where Z is the number of formula units per cell. A primitive cell contains one lattice point, while the conventional cell may contain several to display the full symmetry.

NaCl 为面心立方，Z = 4；CsCl 为简单立方型（Cs⁺ 在体心），Z = 1；金刚石为面心立方加四个四面体空隙，Z = 8；铁（α-Fe）为体心立方，铜、铝、金为面心立方，镁、锌、钛为六方密堆积。

NaCl is face-centred cubic with Z = 4; CsCl is primitive cubic with Cs⁺ at the body centre, Z = 1; diamond is face-centred cubic with four tetrahedral sites filled, Z = 8; α-iron is body-centred cubic, copper, aluminium and gold are face-centred cubic, and magnesium, zinc and titanium are hexagonal close-packed.

晶胞参数由 X 射线、中子或电子衍射峰的位置确定，原子在晶胞中的位置由衍射强度推算。剑桥结构数据库（CSD）收录了 100 多万个有机和金属有机晶体结构，无机晶体结构数据库（ICSD）收录了数十万个无机结构。

Cell parameters come from the positions of X-ray, neutron or electron diffraction peaks, and atomic positions from their intensities. The Cambridge Structural Database holds over a million organic and metal–organic structures, and the Inorganic Crystal Structure Database hundreds of thousands of inorganic ones.