Spin-crossover theory

Paulsen H, Trautwein AX (2004) Density Functional Theory Calculations for Spin Crossover Complexes. 235 197-219 Penades S,see Rojo J (2002) 218 45-92 Perrio C, see Lasne M-C (2002) 222 201-258... 

Density Functional Theory Calculations for Spin Crossover Complexes... 

Keywords Spin crossover Ligand field theory Optical properties Vibronic structure Configurational coordinate... 

H. Paulsen, A. X. Trautwein. Density functional theory calculations for spin crossover complexes. In P. Giitlich H.A. Goodwin, editors. Spin Crossover in Transition Metal Compounds III, volume 235 of Top Curr Chem, pages 197-219. Springer-Verlag, 2004. 

Jahn-Teller effects are rarely adopted in theoretical treatments of spin-crossover phenomena, except Kambara s model for Fe(II) complexes [24] and Bersuker s for Fe(III) complexes [19,25]. In the Kambara theory, abrupt spin-crossover transitions are given an FO => LS character, while gradual transitions are of the HS LS type. However, experimental evidences of cooperative Jahn-Teller transitions (FO HS) have not yet been reported for Fe(II) spin-crossover complexes. Kambara s theory ignores the spin-orbit interaction and appears to overestimate the Jahn-Teller coupling, producing an unphysical (for Fe(II) complexes) FO => HS transition. 

Zhang, Y., Oldfield, E. 57Fe Mossbauer quadrupole splittings and isomer shifts in spin-crossover complexes A density functional theory investigation. J. Phys. Chem. A 2003,107, 4147-50. 

The present chapter is organized in three sections the first section is devoted to basic theoretical backgroimd concerning the spin-crossover phenomenon, viz ligand field theory, thermodynamics and cooperativity the second section reports on some examples that we feel are particularly relevant to illustrate the main directions in which research on synthetic aspects of cooperativity is being directed finally, the third section describes three approaches, up to now reported, concerning spin bistability in supramolecular and molecular systems and memory effect. 

The critical behaviours of higher order satellites near a continuous phase transition are of particular interest, as they provide the opportunity to study the crossover exponents of the respective symmetry breaking perturbations in the spin Hamiltonian. Each order of satellite has an associated order parameter critical exponent given by / = 2 - a -where a is the specific heat exponent, and crossover exponent As an example, if the transition is described by the 3DXY model, then the exponent 2 measures the crossover caused by a perturbation of uniaxial symmetry. For this model, theory predicts that = o P, with... 

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