Integral over space of the type \(\int \psi _{r}\ast \ \hat{H}\ \psi _{r}\ \text{d}\tau \) where \(\hat{H}\) is the hamiltonian operator containing electrostatic potential energy terms and \(\psi \) is a one-electron wavefunction.

*Source: *Green Book, 2nd ed., p. 17 [

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