This is a typical silicate crystal. Unless the unit cell is very small, ball-and-stick display is too complicated for most silicates, and showing the SiO4 groups as polyhedra is usually more satisfactory. The atomic radii used for Mg and Ca are approximately half the ionic radii, which works fairly well as a general practice.
Select the New command from the File menu. See the start of the Tutorials section for general comments.
Dialog - Title/Structure Axes. In the Title field, enter "Diopside". In the Structure axes combo box, select "monoclinic". For the a, b and c axes, enter 9.746, 8.899 and 5.251, and for beta enter 105.63.
Dialog - Symmetry Option. Select Space group from Table.
Sub-Dialog - Symmetry - Space Group from Table. Enter "C2/c" in the H-M Symbol field, and make sure that the radio button for this option is checked. Or, you can select this space group in the list box, clicking on the Select button, and it makes no difference which option (H-M, Hall or Number) is selected.
Dialog - Boundary Option. Select Enter Forms.
Sub-Dialog - Boundary - Enter Forms. Set the Symmetry for boundary forms to Center only. At the bottom of the dialog, Use individual atom distances should be unchecked and all the Lattice translation boxes should be checked. Now click on the Add Forms button.
Sub-Sub-Dialog - Add/Revise Form. For each form, enter the indices shown below in the h, k and l edit boxes, and the distance in the Central distance box. When finished with each, click on the New Form button to go to the next. When done, click on OK.
h k l distance
1) 1 0 0 4.0
2) 0 1 0 7.0
3) 0 0 1 11.0
Back in the Boundary - Enter Forms dialog, check the list and correct the entries if necessary with the Revise button. When done, click on OK.
Dialog - Crystal Forms for Display. In the Display forms group of radio buttons, select Same as boundary.
Dialog - Input Atoms. Click on the Add Atoms button.
Sub-Dialog - Revise Atom.
Atom 1) is silicon. The Label should be Si, the Type should be 14 (the atomic number) and the Radius 0.15 - silicon atoms will not appear by themselves unless skeletal or transparent polyhedra are selected for 3D Drawing modes. The colors and pattern numbers can be ignored for this reason. The x, y and z coordinates are 0.2862, 0.0933, and 0.2293. When done, click on the New button.
Atom 2) is magnesium - Mg and Ca atoms will be shown as spheres. The Label should be Mg, the Type should be 12 (the atomic number) and the Radius 0.36. The x, y and z coordinates are 0.0, 0.9082 and 0.25. The colors can be selected as desired; however black (RGB components 0, 0, 0) is recommended for rims, and red (255, 0, 0) for the fill. For Black-and-white pattern numbers, 15 is recommended for rims and 6 for fills. When done, click on the New button.
Atom 3) is calcium. The Label should be Ca, the Type should be 20 (the atomic number) and the Radius 0.56. The x, y and z coordinates are 0.0, 0.3015 and 0.25. The colors can be selected as desired; however black (RGB components 0, 0, 0) is recommended for rims, and blue (0, 0, 255) for the fill. For Black-and-white pattern numbers, 15 is recommended for rims and 4 for fills. When done, click on the New button.
Now enter three oxygen atoms. For all these atoms, the Type will be 8 (the atomic number) and the Radius will be 0.0 - oxygen atoms only appear as corners of polyhedra, and if they are to be shown as spheres they can be given a uniform radius. The rim color can be black and the fill color cyan (0, 255, 255). For Black-and-white pattern numbers, 15 is recommended for rims and 1 for fills.
The fields which will change between atoms are the Label, and the coordinates (x, y and z). For the first atom, fill in the fields from the values given for atom number 1 below. Then, if you have filled in the remainder of the fields as described in the previous paragraph, click on the New button. For the second atom, all the fields will be the same; replace the values for Label, x, y and z for atom 2) below. In like manner continue on to the third carbon atom.
Oxygen atoms:
4) O1 0.1156 0.0873 0.1422
5) O2 0.3611 0.25 0.3180
6) O3 0.3503 0.0176 -0.0047
When finished with atom 6), click on OK.
Back in the Input Atoms dialog, check the list. If there are any mistakes, you can correct them by selecting the atom and clicking on the Revise button.
Dialog - Polyhedra. Click on Add Polyhedra.
Dialog - Polyhedron Data. The only polyhedron will be the silicate tetrahedron, although is is also possible to do Mg octahedra. The Coordination number is four, the Maximum bond distance can be 1.8, the Central type (Si) is 14 and there is only one Ligand type, 8 for oxygen; put the number eight in the first Ligand type box and be sure the other 6 boxes are empty. The rim color should be black, and the fill color can be yellow (255, 255, 0). Rim pattern should be 15 (black) and fill pattern can be 2. Click on OK when finished.
Back in the Polyhedra dialog, in the Show ligands as spheres group, select the Use single radius radio button, with radius 0.2.
Click on OK if the single polyhedron entry is correct.
Dialog - Bonds. Click on the Add Bonds button.
Sub-Dialog - Bond Data. We will add two bonds. The Atom types, Max. distance and rim color are given below. The Radius should be set to 0.0 for single-line bonds, which will use the rim color and pattern number - the fill color and pattern are ignored. Rim pattern number should be 15. The Min distance field can be set to 0.4 or any small number.
For bond 1), Mg-0, the two types are 12 and 8; the maximum distance is 2.3; and rim color can be blue (0, 0, 255). After entering the values for bond 1), click on New to go to 2). For bond 2), Ca-0, the two types are 20 and 8; the maximum distance is 3.0; and rim color can be magenta (255, 0, 255). Click on OK when finished with bond 2)
Back in the Bonds dialog, correct any mistaken entries. Click on OK when done.
Dialog - End of Mandatory Input. At this point you have the choice of continuing with the dialogs in the Input2 menu, or accepting default values for the parameters in those dialogs. If a structure file was in memory when you started the New input, you can also accept the parameters used in that structure (the current values). Let us continue, to insure that the result is the same as the sample file DIOPSIDE.STR.
Dialog - Crystal Edges. You can select either Both or Atoms only from the Display group. Set the dash length to 0.2 and the dash ratio to 0.45. colors can be yellow (255,255,0) for front edges and blue (0,0,255) for back edges. Pattern numbers for both front and back edges should be 15.
Dialog - Perspective Viewing. Check the box and set the Perspective distance to 50.0.
Dialog - Stereopairs. You can check the box if you like, although you may need a special viewer to see the screen image in 3D.
Dialog - Rims. Check all the boxes. Unshaded drawings look best with rims, and shaded drawings in color usually look better without rims.
Dialog - Line Widths. Click on the Set All to 0 button - this will result in widths of one dot in screen display and raster output. Be sure that the Use Individual check boxes are off.
Dialog - Shading. Uncheck the boxes Shading for atoms, Shading for bonds and Shading for polyhedra. You can switch later to shading.
Dialog - Background Color. A light or medium gray, such as (170, 170, 170) usually works best on the screen.
Dialog - Axes/Unit Cell. In the Display group, select Neither.
Dialog - Thermal Ellipsoid Parameters. Click on Cancel to skip this dialog.
Dialog - Initial Orientation. We want to look almost directly down the c axis, so set the Initial Cartesian rotations (x, y and z) to 0.0, 92.5 and 0.0. Uncheck the Clinographic viewing box.
Dialog - Scaling. Set the Scale mode to Maximize size for each view.
Dialog - Centering/Displacement. Select Automatic Centering.
Dialog - Calculation Output. In the Output combo box, select "No Output".
After the last dialog has been completed, a message box appears saying "New input completed - calculate now?". Click on Yes, and the drawing should appear quickly.
You can compare the results of this input process with the file DIOPSIDE.STR in the \SAMPLES subdirectory. If there are differences, you can print out the input parameters in either or both files with the List Input command in the File menu (Listings sub-menu).