By default, MOPAC will attempt to optimize the geometry. If this is not wanted, then two methods are provided for doing a single SCF calculation and then stopping.
The following data sets illustrate these two methods.
AM1 1SCF Formic acid Example of a single-point calculation O C 1.20 1 O 1.32 1 116.8 1 0.0 0 2 1 H 0.98 1 123.9 1 0.0 0 3 2 1 H 1.11 1 127.3 1 180.0 0 2 1 3 0 0.00 0 0.0 0 0.0 0 0 0 0 AM1 Formic acid Example of a single-point calculation O C 1.20 0 O 1.32 0 116.8 0 0.0 0 2 1 H 0.98 0 123.9 0 0.0 0 3 2 1 H 1.11 0 127.3 0 180.0 0 2 1 3 0 0.00 0 0.0 0 0.0 0 0 0 0 |
The recommended way to do a single SCF calculation is by explicitly using the keyword 1SCF. This will cause MOPAC to do one SCF calculation and then stop. No derivatives will be calculated; if you want them, add GRADIENTS.
An alternative is to set all the optimization flags to zero. This is not the preferred option because the flags might all be set to zero when the data set was created, and if you don't notice that, the results might not be what you expected. By using 1SCF, the user has to make a conscious decision to explicitly request that a single SCF be done. |