User instructions

Installation

Sources (if needed, please contact authors) and binaries should be placed into main directory called „Lattices“. Several code files, fontfiles, and an auxiliary file t2.tcl should be in the subdirectory „Subgroups“. This directory is a working one where the results are stored. The links to the binaries - viewer (vwr.exe), graphical interface (gr.exe) and computing & constructing part (lr.exe) - are made in the working directory.

Running the LAT_SUB software

The program is started by issuing the command ./gr in the working directory. The graphical interface is initiated. It allows user to enter input data (specifying the space group G and its subgroup H) either interactively from keyboard, or from a file placed in the working directory.

Sample data files are provided. When using keyboard, the user is interactively navigated through several pop-up windows and/or menus.

During the process of entering the data, an input file is written; it can be used next time, or may serve as a template.

Space group symbols vs. selection of translation lattice basis

In order to obtain the correct space group symbols, canonical primitive bases of translational Bravais lattices should be used. It is recommended to select a basis of a primitive ('non-centred') translation group T^P according to International Tables for Crystallography, Vol. A, say a,b,c. The bases of centred translation lattices should be given in terms of the basis of T^P as follows:

Supergroup G

    A : a, (b-c)/2, (b+c)/2                           I: (-a+b+c)/2, (a-b+c)/2, (a+b-c)/2

    B : (c+a)/2, b, (c-a)/2

    C : (a-b)/2, (a+b)/2, c                          R:(2a+b+c)/3, (-a+b+c)/3, (-a-2b+c)/3

    F : (b+c)/2, (c+a)/2, (a+b)/2                  [obverse setting should be used]

Subgroup H

For a centred translation lattice select a basis that is consistent with the description given above. That is, for I-centred group the basis used, say a_I,b_I,c_I , should be such that vectors b_I+c_I, c_I+a_I, a_I+b_I would form a basis of a primitive translation lattice that will be equivalent to the basis a,b,c chosen according to the Vol. A International Tables for Crystallography.

Hint

Sometimes it is convenient instead of the subgroup H enter its translational group T₂, i.e. the triclinic group P1 ~ (1,T₂), and use an arbitrary basis of T_2. The group H will appear among subgroups H' ~ (P₂ ,T₂) of G; correct centering of its translation lattice is determined by the program and given in the quotient L₄.