= Molecular orbital
{title2=$\psi(\mathbf r)$}
{wiki}
A <molecular orbital> is a one-<Electron> spatial <wavefunction> for the combined <atomic nuclei> of a <molecule>. For a normalized <molecular orbital>, the <Born rule> gives the position <probability density> $|\psi(\mathbf r)|^2$, with $\int_{\mathbb R^3}|\psi|^2\,d^3\mathbf r=1$. The <molecular orbital> is the amplitude, rather than its squared <modulus> or a classical trajectory.
In the independent-orbital approximation, a doubly occupied <molecular orbital> contributes $2|\psi|^2$ to the <Electron> number density, whose <integral> is two. An empty <molecular orbital> contributes zero, even though its shape is still part of the model. The <molecular hydrogen> example therefore uses one occupied spatial <molecular orbital> for two <Electrons>, distinguished by their <spins>. A negative real <probability amplitude> means a relative <quantum phase> of $\pi$, not positive <electric charge>; multiplying the whole <wavefunction> by $-1$ changes only its <global phase>.
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