Spin crossover in the CsFe^II[Cr^III(CN)₆] Prussian blue analogue: phonons and thermodynamics from hybrid functionals

Middlemiss, D.S., Portinari, D., Grey, C.P., Morrison, C.A. and Wilson, C.C. (2010) Spin crossover in the CsFe^II[Cr^III(CN)₆] Prussian blue analogue: phonons and thermodynamics from hybrid functionals. Physical Review B, 81(18), p. 184410. (doi: 10.1103/PhysRevB.81.184410)

Abstract

Solid-state lattice-dynamics calculations within the hybrid density-functional approach are applied to the study of the thermally induced Fe2+ low spin(LS;S=0)↔high spin(HS;S=2) crossover (SCO) in the extended network of the CsFe[Cr(CN)6] Prussian blue analog. The variations in the thermodynamic parameters defining the SCO transition with the Fock exchange content (F0) of the functional are obtained and discussed, where, in keeping with the findings of previous studies of isolated complexes, it is found that an admixture F0≈14% provides reliable values. The transition is shown to be dominated by the entropy difference, ΔS, associated with the softening of low-frequency vibrational (vib) modes in the HS state, as has been suggested previously for a wide range of SCO materials, more than half of ΔSvib deriving from modes with wave numbers of 250 cm−1 or less. Analysis of the influence of the spectroscopic selection rules upon the apparent SCO thermodynamics reveals that determinations based solely upon infrared or Raman frequencies, or upon their combination, lead to significant errors. The effect upon the SCO transition of the electronic entropy associated with the degenerate Fe2+ HS (eg2t2g4) configurations is also detailed, evidence for the existence of an associated dynamic Jahn-Teller distortion being presented. Optimized structures, bulk moduli, Γ-point vibrational frequencies, and crystal-field energy models are discussed for all relevant spin states.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Middlemiss, Dr Derek and Wilson, Professor Charles and Portinari, Mr Damiano
• Authors: Middlemiss, D.S., Portinari, D., Grey, C.P., Morrison, C.A., and Wilson, C.C.
• Subjects: Q Science > QD Chemistry; Q Science > QC Physics
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Physical Review B
• Publisher: American Physical Society
• ISSN: 1098-0121
• ISSN (Online): 1550-235X
• Published Online: 12 May 2010