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Orbital disproportionation and spin crossover as a pseudo Jahn-Teller effect
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10.1063/1.2346682
/content/aip/journal/jcp/125/10/10.1063/1.2346682
http://aip.metastore.ingenta.com/content/aip/journal/jcp/125/10/10.1063/1.2346682

Figures

Image of FIG. 1.
FIG. 1.

Cross section of the APES along the coordinate for the states arising from the electronic configuration of . Its main features are (as predicted by the theory) a very weak JTE in the excited state, a strong PJTE between the excited and states that produces the global minimum with a distorted configuration, and a second conical intersection along (with two more, equivalent, in the full space). The spin-triplet state is shown by dashed line.

Image of FIG. 2.
FIG. 2.

Conventional energy level scheme for electronic configurations in tetrahedral (also valid for octahedral) vs icosahedral geometries. The and states in tetrahedral symmetry merge to form the fivefold state in symmetry. Vertical arrows show allowed PJT coupling via the indicated normal modes.

Image of FIG. 3.
FIG. 3.

Calculated relative contribution (weight) of the two possible disproportionate distributions the state (that produces the global minima of ) represented by the two Slater determinants, and , in the wave function. At (undistorted configuration) the weights of both components are equal and the electronic density distribution is totally symmetric. As a result of the PJT distortion one of the components becomes dominant, producing an orbitally disproportionate electron distribution.

Image of FIG. 4.
FIG. 4.

The molecule in symmetry.

Image of FIG. 5.
FIG. 5.

Calculated cross section of the APES of using CASSCF along the angle in Fig. 4 showing the very weak JTE in the excited state and a strong PJTE between the and states. The inset shows in more detail the two conical intersections in the state in this direction.

Image of FIG. 6.
FIG. 6.

Ground and excited states of along the coordinate. The PJTE pushes down the component of the degenerate term, which has also a weak linear JTE resulting in two conical intersections in this direction, one at and the other nearby, seen in the more detailed picture in the inset.

Image of FIG. 7.
FIG. 7.

Cross section of the APES of along the mode that distorts the system from square-planar to rhombic geometry due to the PJT coupling.

Image of FIG. 8.
FIG. 8.

Cross section of the APES of along the -mode distortion transforming the system from tetrahedral to square-planar geometry due to the PJT coupling.

Image of FIG. 9.
FIG. 9.

Cross section of the APES of along the effective mode that takes the system from the undistorted high-spin minimum to the distorted low-spin minimum due to the multimode PJT coupling. The zero-point energies (ZPEs) along this mode (which are different from the global ZPEs) are to show that the lowest vibronic state associated with the electronic spin-doublet state is lower than that of the spin-quadruplet state.

Tables

Generic image for table
Table I.

Vibronic and force constants of in the states arising from the splitting of the term of electronic , , and configurations (in notations).

Generic image for table
Table II.

The parameters of the JT spin crossover in several systems. is the energy difference between the ground states of the high-spin and low-spin configurations, and and are the respective energy barriers, the energy difference between the minima and the crossing point between the two spin states (Fig. 9). All the energies are read off the zero-point vibrations.

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/content/aip/journal/jcp/125/10/10.1063/1.2346682
2006-09-08
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Orbital disproportionation and spin crossover as a pseudo Jahn-Teller effect
http://aip.metastore.ingenta.com/content/aip/journal/jcp/125/10/10.1063/1.2346682
10.1063/1.2346682
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