8.3 Mopac calculation

This dialog window allows to run the Mopac semi-empirical calculation. Press the Run button to start the calculation, otherwise press Cancel to close the dialog. Please note that the Mopac executables are included in the standard VEGA ZZ package. If you want use another Mopac version, you must replace the included executable placed in the VEGA ZZ installation folder with the new one.
When you press Start, a file requester is shown in order to select the output file. Mopac runs in background and VEGA ZZ remains fully functional. When the calculation ends without errors, the processed structure is automatically reloaded. To abort a Mopac calculation, use the Task Manager or click with the right mouse button on the 3D view and select Stop calculation.
Checking Update the 3D view, available only if Mopac2007 is installed, the molecule structure is automatically updated during the calculation and the progress is shown in the console (step number, energy and gradient).

Mopac Calculation

 

8.3.1  Parameter fields

With these fields you can specify the type of calculation (AM1, MINDO/3, MMDO, PM3 and PM6, RM1 if Mopac2007 is installed), the total charge (if the pre-calculated charge is wrong) and the extra keywords (Other field). The default parameter is AM1 and the total charge that is calculated using the atomic partial charges if they are already assigned, otherwise is calculated on the basis of the charge group recognition. Is it possible that the molecule has wrong or incomplete atomic charges and so a wrong value is shown. To force the group-based total charge calculation, the user can click the Calc. button.
When Mopac2007 is installed, it's automatically recognized and the graphic interface adapts itself to the new features (e.g. PM6, RM1 etc). Mopac2007 isn't included in the VEGA ZZ package and it can be installed follow these steps.

 

8.3.2 Switches

They are the main switches for Mopac calculation. To understand what they mean, please read the Mopac Manual.

Switch Description
Precise Increase the criteria for terminating all optimizations by a factor, normally 100.
GEO-OK Override some safety checks (e.g. in the structure geometry).
MMOK Use the molecular mechanics correction for the amidic bonds (CONH). It can be automatically switched on if an amidic bond is detected.
1SCF Do a single point energy calculation.

 

8.3.3 Limits

VEGA ZZ includes two versions of Mopac 7.01-4: Mopac_50_100.exe (max 50 heavy atoms and max 100 hydrogens) and Mopac_100_200.exe  (max 100 heavy atoms and max 200 hydrogens). The two executables are selected automatically by VEGA ZZ  for a balanced use of the hardware resources. No more than 300 atoms (100 heavy atoms + 200 hydrogens) can be used by VEGA ZZ in Mopac calculations. These limits can be superseded installing Mopac2007 (for more information, click here).