User`s guide

3. Running Jobs
Advanced Mopac Options Page
The Symmetry Number of the molecule may be specified for thermochemistry calculations. A
Solvent may be specified, although this significantly increases the calculation time. For a Saddle
Calculation, the Second Geometry must be specified by supplying its job number. The default
specification of molecular geometry is with a z-matrix; however, Cartesian Coordinates may be
used instead. Mopac carries out the calculation in the coordinates that are used to specify the
molecular geometry. A filename of External Parameters may be supplied. CPU% specifies
what fraction of the CPU this job should consume. Specifying 100% claims exclusive use of the
computational server, whereas specifying 50% would permit another 50% job to run
simultaneously on the same server. Additional Keywords permits the specification of additional
keywords in the keyword section. Some useful additional keywords are
PRECISE - Tighten convergence criteria
MMOK - Add a mechanics correction to amide linkages
GEO-OK - Allow atoms to be closer than 0.8 Angstom
F. Failed Calculations
When running computational chemistry jobs, especially on new molecular systems, it is inevitable
that some jobs will fail. After diagnosing the cause of failure, changes can be made that allow
most jobs to run successfully.
The most important step in analyzing a failed job is to view the output file by clicking Raw
Output in the Job Manager. The cause of failure will usually be indicated near the end of the file.
Once the cause of failure is identified, appropriate corrective action can be taken.
Some common causes of job failure (and possible solutions) include:
• A job exceeding the maximum job time limit (use a lower theory or smaller basis set)
• Incorrect specification of charge or multiplicity (specify correctly)
• Change of molecular symmetry during the calculation (choose Disable Symmetry from
the Advanced Options)
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