Valence-Rydberg state mixing

The dependence of the Fermi-sea on symmetry, spin, and the parameters of the Hamiltonian. Valence-Rydberg state mixing... 

In the early 1970s, when it had been recognized that experiments of beam-foil specfroscopy could produce lifetimes for many types of atomic transitions, we carried out a number of computations and analyses of transifion probabilities in atoms, with and without heavy valence-Rydberg state mixing. As we wrote in Ref. [26b], fhaf work revealed that (non int) corresponds to correlation vectors with small coefficients which are reasonably well decoupled from T and (int). This implies A) Their direct contribution to (, D /) is very small. I.e., the last three terms of eq. (12) are negligible because of the small... 

One of the severe bottlenecks of the CASPT2 approach is the size of the active space. It is very hard to perform calculations with more than 12 active orbitals when the system has no symmetry. With symmetry it is possible to extend the practical limit to 13 or 14, but above that the calculations become too heavy. When studying only one energy surface, it is rare that more than 12 active orbitals are needed to describe the near-degeneracies in the system. Calculations in spectroscopy are, however, more demanding. Different orbitals are active in different excited states. Most electronic spectra have Rydberg states mixed in with the valence states. Thus Rydberg orbitals have to be included. As an example, consider the molecule methylenecyclopropene (MCP) [(1) in Fig. 3], the spectrum of which is discussed in more detail below. A... 

The extensive calculations of Serrano-Andres et al [31] have shown a spurious valence-Rydberg mixing in the CASSCF wave functions when valence (7t,7r )and Rydberg orbitals are optimized all together in a state average calculation it was shown that these orbitals loose their diffuse character and instead tend to provide an extra correlation to valence orbitals. To avoid such interaction, the orbitals used for the Cl treatment of the electronic spectrum were obtained by a two step procedure ... 

It thus appears that a judicious application of correction curves of the form of (III.l) can transform a uniform set of ab initio potential-energy curves into a set of corrected curves that are very representative of the actual system. Such curves must be of similar chemical character such as all valence states or all Rydberg states. Rydberg-valence mixing cannot be easily accounted for in ab initio calculations, and simple empirical corrections do not seem possible for such situations. 

In this chapter we have implicitly assumed the Rydberg atom to be a one electron-atom. In the perturbed Rydberg series of, for example, alkaline earth atoms, Rydberg states can have mixed valence-Rydberg character. In such states the black body effects are reduced by a factor equal to the fractional Rydberg character.14... 

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