## 1.2.1. FEATURES OF BALSAC/LATTICE

next, previous Section / Table of Contents / Index BALSAC/LATTICE uses a lattice definition and appropriate Miller indices to construct sections of lattice planes which are displayed as 3-dimensional arrays of atoms for visual inspection and interactive analysis. The program allows you to study lattices (both primitive and non-primitive, with up to 200 atoms per unit cell) and comes provided with several standard lattice structures predefined internally. Lattice planes are described by appropriate Miller indices (h k l). For fcc and bcc type lattices (h k l) can be defined with respect to simple cubic lattice vectors (commonly used) as well as to Bravais reciprocal lattice vectors. For hcp and Graphite structures a 3- and 4-index notation, (h k l) and (l m n q), is implemented. The bottom/top plane of a lattice section can be selected freely to allow for surface planes of different termination in non-primitive lattices. Any number of selected planes may be completely restructured (including 3-dimensional shifts, modified planar periodicities, modified atom basis sets) to allow for most general geometries. BALSAC/LATTICE contains various graphical options to visualize structural properties. Lattice sections of variable size and shape (blocks or spherical cuts) are displayed either layer-by-layer (net plane stacking) starting with a selected plane, atom-by-atom as 3-dimensional arrays of atoms, or as arrays of elementary cells starting with the atoms farthest away from the viewer. Atoms can be visualized by dots, (filled) circles, or (shaded) spheres (with/without sticks connecting atoms) and may be labelled/painted according to their layer or element label. A 3-dimensional impression of the structure is given by parallel or central projection where the viewing direction and position can be chosen freely. The structural impression can be further improved by red/blue stereo viewing (using color filter viewing glasses) or by full color stereo viewing (with optical stereo viewing glasses). Various manipulations of the graphical output such as size reduction / enlargement, rotation about the viewing direction, or changes in perspective are readily available. Further, atom coordinates, distances, angles, local symmetries, geometries, and subplanes of a lattice section may be read off from the screen by selection via a graphical pointer (keyboard or mouse). Apart from graphical output, numerical coordinates of all atoms of given sections can be listed and saved for separate graphical or numerical applications. (This feature allows you to run BALSAC without a graphics adapter.) Numerical information on lattice sections (such as real and reciprocal lattice vectors, transformed basis vectors, restructure information, atomic coordinates etc.) determined by BALSAC/LATTICE can be saved on separate files. These files may be transferred to the BALSAC/CLUSTER part (see below) or modified externally with text editors and used as input for subsequent runs of BALSAC or other programs. BALSAC/LATTICE is fully menu-driven in interactive mode using keyboard or mouse input and is mostly self-explanatory. The user may start from scratch building any lattice or use predefined lattice structures or he/she can start with structures generated by previous runs. In batch mode BALSAC/LATTICE runs by itself using input from an ASCII file which was generated in a preceding session or written with a text editor or produced by other programs. This feature allows you to interface BALSAC with other application programs. In batch mode the program simulates an interactive session defined by a set of option parameters and input data taken from the input file. Most of the important manipulations of the interactive mode of BALSAC/LATTICE such as changing lattices, Miller indices, views, graphics options etc. are possible in batch mode. Switching between interactive and batch mode is always possible if appropriate data transfer files for in/output are provided. BALSAC/LATTICE allows file output of structure and graphics data in various ASCII formats for subsequent use with BALSAC as well as with other professional visualization programs (SARCH, LATUSE, PLOT3D, SCHAKAL, etc.). This includes encapsulated color PostScript format for generating structure graphics. BALSAC PostScript files are written specifically for good readability and easy editing to further modify/embellish structure plots. Amongst other applications, BALSAC/LATTICE is particularly useful to - quickly explore a variety of bulk structures and terminations, both qualitatively and quantitatively. - visualize lattice sections of various shapes with planar and spherical boundaries, allowing to show - crystal blocks with planar surfaces, - hemispherical lattice sections describing facetted FIM, FEM, or STM tips, - spherical crystal sections describing clusters, - spherical cavities inside crystals. - inspect and analyze local geometries and symmetries of any (h k l) oriented surfaces in complex lattices, with or without adsorbates, including surface restructuring (layer relaxation, commensurate/ incommensurate reconstruction).In particular, lattice planes of large Miller index values describing stepped / kinked surfaces are accurately accounted for. (All basis vectors are determined using integer algorithms based on solutions of diophantene equations rather than by direct vector operations). - generate instructive high quality (color) graphics of complex lattice and surface geometries for presentations and publications. next, previous Section / Table of Contents / Index