Data defining a calculation are supplied to MOPAC in a file called the data-set or simply input file. This file is named [filename].dat where [filename] is a name given by the user.
The input file is the only file which must be present. Other files may need to be present if specified by the input data. For example, if the input contains the keyword "RESTART", then the restart ([filename].res and density ([filename].den) files must exist.
In a normal simple job, only two files are produced: the results file [filename].out and the archive file [filename].arc.

Overview of Data-Set

Data-sets consist of at least three parts: one keyword line, two comment lines, and geometry data:

• Line 1: Keywords (one line). These control the calculation. The number of keywords used, can range from none to about 20, space permitting. When more keywords are needed than will fit on one line, more lines can be used (see keyword "+").
• Line 2: Description of the calculation, e.g. the name of the molecule.
• Line 3: Any other information describing the calculation.
• Line 4, 5, ...: Internal or Cartesian coordinates (one line per atom).
• Last line: Blank line to terminate the geometry definition.

Definition of keywords

There are three classes of keywords:
• those which control substantial aspects of the calculation, i.e., those which affect the final heat of formation,
  
• those which determine which output will be calculated and printed, and
  
• those which dictate the working of the calculation, but which do not affect the heat of formation. The assignment to one of these classes is designated by a C, O or W, respectively, following each keyword in the keyword list.

• MOPAC 6 at Darmstadt
  
• MOPAC 6 at the Ohio Supercomputer Center Gopher site
  

Last updated on August 13th 1996