# What is "physicist's water"?

There is a statement on page 60 of this dissertation:

the "physicist's water molecule" ($\ce{O-H = 1.1 \mathrm{\mathring{A}}, \angle HOH = 104^\circ}$)

I understand it to be a model similar to the "spherical cow in a vacuum,", in that it's meant to be an easy-to-remember approximation, but

• What is the etymology of this phrase or definition?

• Why this specific choice of parameters? It could just as easily be $\pu{1.0 \mathrm{\mathring{A}}}$, according to Wikipedia, and the angle could vary as well.

• Googling the phrase "physicist's water molecule" yields the dissertation cited as the only hit. So it seem like a phrase the author invented.
– MaxW
Nov 18 '17 at 1:02
• That's a (odd) phrase, not a definition. Obviously you cannot define a water molecule, physicist's or other's, as it is given by nature.
– Karl
Nov 18 '17 at 9:01
• @Karl I disagree; I think it is a definition in the same way that linear water or planar ammonia are definitions. It is supposed to invoke some well-defined picture in your mind, even if it isn't physically sensible most of the time. Nov 18 '17 at 22:10
• (What would you do with a linear water molecule? Not even didactically useful.) I just checked the values for actual water, and they are 0.958 Angstroms and 104.45°. A spherical cow is a useful appoximation, as it simplifys modeling the cow. Using very imprecise values to stick into a computer simulation is however simply stupid imo, and using a wrong value like 1.1A is terribly stupid. I don't know what the author of that dissertation was thinking, but i wager it wasn't much. Tried and failed to sound clever, with that phrase.
– Karl
Nov 19 '17 at 8:32
• (Or is he simply using those values as starting point to successfully refine better values? In that case I take back anything I said about stupid. Sorry, too lazy now to read the diss myself.)
– Karl
Nov 19 '17 at 8:34