Vibrational clamped-nucleus

In the second approach, the so-called clamped-nucleus treatment, the effect of the perturbation on the electronic and nuclear motion is treated sequentially. First, the Born-Oppenheimer approximation is applied to the vibronic wavefunction of the ground state, ov ri, Rk ), which is therefore expressed as a product of an electronic wavefunction o( ri Rk ) vibrational wavefunction (. R/f )... 

For polyatomic molecules the electronic polarizability in the clamped-nucleus treatment is frequently expressed as the polarizability evaluated at an equilibrium geometry Rk,s plus a vibrational correction Aa ... 

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