What is it used for?

In practice MOPAC is used:

to optimize a structure

-variables to be optimized are followed by the "1" flag in the input file.

to obtain a description of the molecular orbitals, coefficients, charges.

-the keywords VECTORS and LOCALIZE will print the coefficients in the output file.

to perform a line search, describing how the energy (heat of formation) depends on one variable (distance, angle, torsion)

-the variable to be scanned is marked by a "-1" flag.

-values are added at the bottom of the input file.

-MOLDEN can visualize the output of a line search (plot and structures)

to do a grid search, varying two variables

-the number of points and the step size are specified in the keyword line.

-the data from a grid search can be plotted by e.g. Gnuplot.

to search for transition states in reactions

-e.g. optimize the maximum resulting from a line search, or the saddle point in a grid surface.

Last updated on August 22nd, 1996