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MOPlot is a handy visualization application specially designed for fast molecular orbitals plotting from the outputs of the Gaussian 03/98/94, Molcas, Gamess/US quantum chemical calculation packages. This Molecular Orbital Plotting Program will prove to be easy-to-use and very efficient.

MOPlot can display:
· Geometries, including the Cartesian coordinate axes, atom numbers according to the geometry definition in the calculation. Molecules can be turned in all directions under mouse control, or, for more precision, using the controls in the "camera" menu. Bonds can be displayed as cylinders or as simple lines.
· Mulliken atomic charges, group charges (charges of hydrogens summed into heavy atoms), and atomic spin populations (for open shell systems), if the corresponding information is available in the output of the calculation.
· Molecular orbitals (hence the name of the program), according to the protocol defined by Haselbach and Schmelzer and described below. MO's can be from RHF; UHF alpha/beta (cf switch in the "MO" menu), or CASSCF calculations. SCF MOs are ordered by energies, CASSCF MOs or natural orbitals are ordered by occupation numbers.
· Normal vibrations, both as displacement vectors and in animated form. For complex molecules where the calculation of the displacements may become slow, a "loop" mode is available to speed up the animation.
· The gradient difference and derivative coupling vectors at conical intersections, as well as any linear combination of the orthonormalized vectors.

In addition, MOplot can:
· Compute geometric parameters (bond lengths, angles, dihedrals) for any set of atoms or midpoints between two atoms (the latter is a unique feature of MOPlot).
· Plot the energy change in the course of a geometry optimization or a "scan" run (similar to Molden). The geometry at each step of the optimization can be displayed and saved to a file.
· Form linear combinations of vibrations. This feature is useful for example to visualize the circular movement of atoms along degenerate normal modes (presently the different frequencies of non-degenerate modes are not taken into account).
· Generate (interpreted or encapsulated) postscript output in vector format, using a flat or a pseude-3D shaded mode. Pages can be configured to hold multiple images of any kind that can be displayed on the screen. MOPlot output can thus be imported into most current drawing programs (Adobe Illustrator, CorelDraw ?) for further processing.
· Recognize output from Gaussian 94/98/03 calculations, and input to the Molden viewing utility, such as it is for example generated by the Molcas program. In addition, we have defined a proprietary standard format which MOPlot also recognizes. Users who want to interface MOPlot to their favorite quantum chemical program should write scripts that convert the output of that program into the standard format.
· Be freely configured by the user with regard to colors and fonts that appear in the various displays. In addition, a toggle is available to switch between color and b/w renditions, e.g. for publication purposes.