3.3.4.1. BALSAC/LATTICE SESSIONS

next, previous Section / Table of Contents / Index In order to learn about the numerical analysis of lattice sections using graphics output of a BALSAC/LATTICE session you restart BALSAC with input from the backup file 'balsac.lat' which you have created in Sec. 3.3.1. To do this you start BALSAC from the command line with options as balsac -lr or balsac -l balsac.lat Both commands tell BALSAC to load the structure file 'balsac.lat' and move to the BALSAC/LATTICE main option menu. Pressing [X] produces a plot of the ZnS(0 0 1) surface as shown before. After plotting has been completed and the option menu shows at the bottom of the screen you enter the graphic analysis by pressing [Q] which displays a one-line menu Analyze[DVRAEPMN_B_WG] build[L!_CK] draw/view[Z_IJ_FSQ+] [?,]esc at the bottom and a graphical pointer (standard mouse graphics pointer, "arrow", or crossing lines, "+", if no mouse is available) shows at the center of the screen (maybe only after an analysis option has been selected below). Now you can analyze each visible atom on the screen, obtain distances between two atoms, or angles and planar directions defined by three atoms using the graphical pointer. Let us try it out. First you select the distance analysis requiring two different atoms by pressing [D]. This allows you to move the graphical pointer on the screen by moving the mouse up/down/left/right on the table or by pressing the cursor keys (arrow up/down/left/right or number keys 2/8/4/6, see Sec. 5.5). Pressing [+] or [-] increases/decreases the step size of the pointer movement in keyboard mode. When the pointer points at the surface of an atom sphere (not necessarily the atom center itself) this atom can be analyzed by clicking the left mouse button (L-click) or by pressing [enter]. You choose the Zn atom (small sphere) of the topmost layer closest to you and L-click or pressing [enter] marks the location you selected by a white "+" and shows a line 1: Xyz,R,Id( 110)= 1.7677670 2.4748737 1.5000000 0.139644 30/Zn 1 at the bottom of the screen. This tells you that you have selected as the first atom the 110th atom of the section located at (1.7678, 2.4749, 1.5000) in cartesian coordinates, with a sphere radius equal to 0.1396, element name Zn and nuclear charge = 30, and which is described by the first lattice basis vector ("1" at the end of the line). Next you point at the Zn atom of the topmost layer to the right of atom no. 110. L-clicking or pressing [enter] shows the second atom as 2: Xyz,R,Id( 106)= 1.0606602 2.4748737 1.5000000 0.139644 30/Zn 1 Since by now you have selected two different atoms you can perform the distance analysis by clicking the right mouse button (R-click) or by pressing [X]. This yields (X,Y,Z),LV = (-0.70710678 0.00000000 0.00000000) 0.70710678 telling you that atoms 106 and 110 are connected by a vector (-0.7071, 0.0000, 0.0000) in absolute cartesian coordinates and of length 0.7071. If you had selected the lattice direction analysis (selecting [M] in the analysis menu) pointing at atoms 110, 106 and R-clicking or pressing [X] would have shown (hkl) = (-0.2500 -0.2500 -0.5000) (-0.5000 -0.5000 -0.0000)c indicating that the vector connecting the two atoms can be described by a linear combination (-0.2500 -0.2500 -0.5000) of Bravais reciprocal lattice vectors and (-0.5000 -0.5000 -0.0000) of simple cubic reciprocal lattice vectors. So this vector points parallel to the cubic (-1 -1 0) crystal direction. You can repeat this analysis as many times as you like by selecting other atoms. This allows you to examine the complete visible part of the lattice section in a straightforward manner. If you R-click or press [M] after an analysis step is finished BALSAC returns to the analysis menu offering other analysis types. Try as an exercise the distance/angle analysis (selecting [V] from the graphical analysis menu) or the net plane decomposition (select [N]) which require three atoms or the neighbor shell analysis (select [E]) which requires one atom. For further explanations consult Sec. 6.2.14. R-clicking or pressing [,] in the graphical analysis menu finishes the graphic analysis and allows you to continue with plotting or return to the BALSAC/LATTICE main option menu. next, previous Section / Table of Contents / Index