- Both
`aoforce`and even more`Numforce`require well converged SCF-/DFT-calculations (e.g.`$scfconv 8`

and`jobex [-ri] -gcart 4`

). - The maximum core memory the program
`aoforce`is allowed to allocate should be defined in the data group`$maxcor`; the recommended value is about 50% of the available (physical) core memory (in case of RI-calculations subtract the memory specified in`$ricore`). - To start
`aoforce`in the lowest eigenvalue search mode, use the keyword`$les`. For its use as well as other keywords dealing with the calculation of only some irreps, see the Referenceguide part of this manual. `Numforce`additionally requires the file`gradient`

and will not work, if the calculation is not done at a stationary point of the molecular total energy. For reliable results, always use`Numforce`with the option`-central`

(i.e. central differences) and be aware of effects due to the step length (option`-d`

*real*;, default value is 0.02a.u.). It is strongly recommended to use`Numforce`in DFT calculations only with the option`weight derivatives`in`$dft`, since this provides more accurate gradients and thus frequencies, see Section 14.2.8.- The
`Numforce`script can be run for different levels of theory, which means that the binaries it calls have to be specified additionally. To perform calculations using the RI approximation, call`Numforce`with the option`-ri`

. MP2 and CC2 calculations are requested via the options`-level mp2`

and`-level cc2`

, respectively. To select the correct option(s), use the explanations you get by calling`NumForce -h`

.

For a review of theory and implementation see refs. [104,105].