As all the bells sound, the common explanation of geometry of a molecule (consider the water molecule) is due to overlaping electron density.
The valence bond theory of the water molecule describes the two O-H bonds as resulting from the overlap of the H 1s orbitals with the two half-filled 2p orbitals of the oxygen atom. Since the two 2p orbitals are at right angles to one another, valence bond theory predicts a bent geometry for the water molecule with a bond angle of 90°. To do this, draw the following picture:
The opening of the angle to a value greater than the predicted one of 90° can be accounted for in terms of a lessening of the repulsion between the hydrogen nuclei.
But what do we have in MO-LCAO (aka HF) theory?
Methods of quantum chemical calculations give us the following picture of orbitals
For me personally, the picture of molecular orbitals in the second case does not at all agree with the picture of atomic orbitals in the first case. How can you identify the first in the second picture? Or in other words, how does the MO-LCAO (aka HF) theory explain the direction of valence bonds?