Why always 180°?

1

Good day. I’m just starting with PSI4, and I’m trying to optimize simple water molecule’s geometry. Nevertheless, the hydrogens are always at 180°, and we know that is not the optimal geometry. It should give something like the next image as result:

The code I’m using is:

memory 250 mb

molecule h2o {
  O 
  H 1 0.96
  H 1 0.96 2 180
}

set basis cc-pVDZ

op, wfn = optimize('hf', return_wfn=True, molecule=h2o)

molden(wfn, "op.molden", density_a=wfn.Da())

What should I do differently so the optimization gets a little more “real”. Maybe some kinetic energy added to it? (room temperature or so).

Thanks a lot, good bye!

2

The optimizer detected that the input geometry has D_inv_h symmetry and will not take any steps that break that. If you just nudge it out of D_inv_h (e.g. 179.9) it’ll find the correct geometry.