Perturbation Treatment of the Lithium Ground State

Let us carry out a perturbation treatment of the ground state of the lithium atom. 

We found in Section 10.5 that to satisfy the Pauli principle the ground-state configuration must be l5 2s the correct zeroth-order wave function is (10.40)  

To find we must evaluate ( // 0 ). We begin by grouping together terms in  

Because of the orthogonality of the different spin functions in A, B, and C [Eq. (10.12)], the last six integrals in (10.51) are zero. Since the spin functions are normalized, summation over spins in the first three integrals in (10.51) gives unity. Tberefore, 

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Section 10.7 Perturbation Treatment of the Lithium Ground State 297... 

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