ABSTRACT
From equation (2.75) for Ĥ rve, we see that the rovibronic Schrödinger equation (2.76) does not involve molecular parameters, such as bond lengths and angles, and that the only quantities occurring are the masses and charges of the l particles (nuclei and electrons) that make up the molecule. Thus, we can easily set up the Schrödinger equation for any molecule. One might think that we could then simply use numerical methods to solve it. However, even using the most efficient numerical methods, current computers do not have enough power for this to be possible with the required precision except for three- and four-particle systems such as H 2 + https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315273334/90d251cd-96eb-444c-8581-8842f96b239c/content/eq233.tif"/> and H2. This will change as computer power increases.
For most molecules, to solve the rovibronic Schrödinger equation accurately, we are forced to make approximations and then to correct for them as best we can. The approximations introduce concepts that allow us to understand molecules.
