Cell Lattice Vectors

The cell lattice vectors may be specified in Cartesian coordinates or in terms of the lattice vector magnitudes and the angles between them ( $a, b, c, \alpha, \beta, \gamma$). Only one of LATTICE_CART and LATTICE_ABC may occur in a cell definition file.

The definitions of these keywords are as follows:

%BLOCK LATTICE_CART
[units]

$$\begin{array}{ccc} R_{1x} & R_{1y} & R_{1z} \\ R_{2x} & R_{2y} & R_{2z} \\ R_{3x} & R_{3y} & R_{3z} \end{array}$$

%ENDBLOCK LATTICE_CART

Here $R_{1x}$ is the x-component of the first lattice vector, $R_{2y}$ is the y-component of the second lattice vector etc.

[units] specifies the units in which the lattice vectors are defined. If not present, the default is Å.

%BLOCK LATTICE_ABC
[units]

$$\begin{array}{ccc} R_{a} & R_{b} & R_{c} \\ R_{\alpha} & R_{\beta} & R_{\gamma} \\ \end{array}$$

%ENDBLOCK LATTICE_ABC

Here $R_a$ is the value of $a$, $R_\gamma$ is the value of $\gamma$ etc. If the lattice is specified in this manner, the absolute orientation is arbitrary. In this case the orientation is defined by applying the following constraints:

• a lies along the x-axis
• b lies in the xy plane
• c forms a right-handed set with a and b

[units] specifies the units in which the lattice vector magnitudes are defined. If not present, the default is Å. Angles should be specified in degrees.