Single point calculations¶

A single point calculation is the simplest task available in the AMS driver. It simply runs the engine once for the given geometry. In other words, the AMS driver does not explore the potential energy surface (PES), but simply samples a “single point” of it.

A single point calculation is performed by selecting it with the Task keyword:

Task SinglePoint

Note that a single point calculation in AMS includes the calculation of PES point properties. Many of these, such as the nuclear gradients and the Hessian, are derivatives at this PES point with respect to nuclear displacements. These derivatives might be done numerically by the AMS driver, in which case it would technically run the engine multiple times and sample PES points around the initial point. However, in AMS this is still considered a single point calculation. Take for example the calculation of the normal modes of vibration of a molecule. This used to be a separate task in the 2017 release of the DFTB program, but in AMS is just a single point calculation with a request for normal modes:

Task SinglePoint

Properties
   NormalModes True
End

See the manual section on PES point properties for an overview of which properties can be calculated with the SinglePoint task in AMS.