Page 283 - Strategies and Applications in Quantum Chemistry From Molecular Astrophysics to Molecular Engineer
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266 M. TADJEDDINE AND J. P. FLAMENT
• If the excited state is a valence state, without Rydberg character, its contribu-
tion to the polarizability may be important and sometimes essential. This is
the case of the first state.
• If the excited state presents an important Rydberg character, its contribution
is very weak and is even negligible. For instance, this is the case for all the
states states but the 7 and 8 ones.
To summarize, if the low–lying states connected to the ground state by allowed dipole
transition are not valence states but present a predominant Rydberg character, we
have to introduce a lot of states; if not, the value of dynamic polarizability near
the first resonance is poor.
To circumvent this difficulty, we have developed a procedure which allows us to reach
an extrapolate value of a from a finite number N of low–lying true spectral states
We have shown that (1) :
1. Within the limits of a complete molecular basis set with exact the
coefficients of tend to zero as N becomes infinite.
2. We can write an extrapolation formula of the form
