Spin-correlated crystal field

SCCF spin-correlated crystal field K isothermal compressibility... 

Another possibility to address the problem of the correlation crystal fields is an approach based on different wavefunctions for the spin-up and spin-down electrons. This spin-correlated crystal-field model merely doubles the number of crystal-field parameters and thus can be applied in most cases. Shen and Holzapfel (1995c) presented a high pressure study on spin-correlated crystal fields in MFCl Sm2+ (M = Ba, Sr, Ca). In particular, they considered the splitting ratio R of the 5Di and 7Fi multiplets, which should be equal to 0.298 within the conventional one-electron crystal-field theory and independent of the host crystal. In a first step, Shen and Holzapfel (1995c) considered ambient pressure as well as high pressure data of the isoelectronic Eu3+ ion. In this case they found a ratio of R = 0.238, which could be explained by taking into account a spin-correlated crystal-field parameter C2 = —0.007(3). 

Spin-correlated crystal field 276 4.5. The configuration interaction model ... 

The LCCF is a trademark. First introduced by Yeung and Newman (1987), it is based on a concept analogous to the spin-correlated crystal field, and consists in replacing Si iS by Ir in the above formula. This model proved its efficiency in eliminating the discrepancy of the D2 levels of Pr in LaCb. R id (1987) showed that I is a... 

SCCF, see spin-correlated crystal field under crystal... 

However, applying the same model to the high-pressure results for Sm +, extreme deviations were encountered. The authors attributed these deviations to a breakdown of the spin-correlated crystal-field model for Sm " ". As the reason for this failure, configuration interactions with the 4f 5d configuration were determined. These interactions are expected to be much stronger for Sm " ", because the energy of the excited configuration is much lower (at about 20 000 cm ) than in the case of Eu + (at about 50 000 cm ). 

Judd (1977a) proposed that a large part of the correlation effects may be parametrized as a spin-correlated crystal field (SCCF). SCCF is based on the observation that crystal-field parameters seem to be dependent on the spin multiplicity of a term, and considers correlations which result from a difference in the crystal field seen by 4f electrons with different spins y, relative to the direction of the total spin 5 (5 = 2, ... 

Here we comment on the shape of certain spin-forbidden bands. Though not strictly part of the intensity story being discussed in this chapter, an understanding of so-called spin-flip transitions depends upon a perusal of correlation diagrams as did our discussion of two-electron jumps. A typical example of a spin-flip transition is shown inFig. 4-7. Unless totally obscured by a spin-allowed band, the spectra of octahedral nickel (ii) complexes display a relatively sharp spike around 13,000 cmThe spike corresponds to a spin-forbidden transition and, on comparing band areas, is not of unusual intensity for such a transition. It is so noticeable because it is so narrow - say 100 cm wide. It is broad compared with the 1-2 cm of free-ion line spectra but very narrow compared with the 2000-3000 cm of spin-allowed crystal-field bands. 

K GiQ correlation crystal-field parameters S total spin angular momentum... 

Searching along the lines of selective modification of the radial wavefunctions, Newman (1970) and Judd (1977b) found another source of correlated crystal field in the exchange forces between 4f electrons with similarly directed spins. They introduce a correction of the type s, S (where s,- is the zth electron spin and S the total spin) as a multiplicative factor to apply to the operators. The effective crystal field Hamiltonian therefore becomes ... 

In fact, spin-correlated and orbitally correlated crystal field are not two different correlation actions both are part of the more general correlated crystal field described... 

---