Hi Everybody,

I would like to run a geometry optimization with additional harmonic (quadratic) constraints.

The goal is to optimize the most strained part of an input conformation only. Aiming see which part of the molecule relaxes most and in which direction. Other QM packages have the same feature (Gaussian, Gamess).

Internally the geometry optimization adds a quadratic potential to the deviation from the input geometry.

eg.

```
- if atom1 is in its original x,y,z coordinate it gets a penalty of 0
- if atom2 is 0.1A from its original xyz position a penalty of
k * (0.1)^2 is added to the total energy
```

k would be a user defined parameter.

Ideally this could be done on a whole molecule (all atom have the same k) or per atom basis (each atom could have a different k).

Does anybody know if this is doable in Psi4 or how difficult it would be to implement?

Thanks,

Alberto