12. I don't get the contour plot that I'm expecting.

Without knowing the problem, the most common cause of weird-looking plots is the location of the plane of the contour plot. An often overlooked trick in HyperChem is to use "selection" to define the plane for the plot (after calculating the wavefunction without a selection!) The plane for the plot is parallel to your screen and relative to the center of mass of the selection or of the whole system if there is no selection. (You can see the centre of mass of the selection via Display/Show Inertial Axes.) The offset of the plane from the centre of mass is set in the Grid Control dialog box.

Thus to get "good" plots:

1. Get the structure that you want plots for in the workspace.
2. Align the molecule and your view.
3. Clear the selection or select the subset to be treated with QM.
4. Do a single point.
5. Select an atom that you want the plot to pass through.
6. Set Plane offset to 0 in the Grid Control dialog box (and bump up grid points to at least 60 x 60) and plot.

Repeat 5 and 6 to build up a 3D understanding of the property. You can also change the view (NOT molecular coordinates) and replot.

If you still think that the plots look like there is bug in the program, please send email to support@hyper.com, or FAX +1 352 371-3662. Note that for problems with semi-empirical methods per se, we only implement established, published methods from the literature in HyperChem, and improving these methods is not part of our product support!

Note that a bug has been found in electrostatic potential plotting of HyperChem Release 2, 3 and 4 for large systems. The electronic contribution is subject to an integral cutoff threshold, but the nuclear contribution is not. Thus for distances more than ~10 Angstrom from the center of a large molecule, the potential will only be shown as positive, and this will "swamp" the potential closer to the center. This has been fixed in HyperChem Release 4.5.

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