Magnetic susceptibility of alkali-tetracyanoquinodimethane salts and extended Hubbard models with bond order and charge density wave phases

作者：Manoranjan Kumar, Benjamin J. Topham, RUIHUI YU, Quoc Binh Dang Ha, Z. G. Soos · 发表于：The Journal of Chemical Physics · 年份：2011 · DOI：10.1063/1.3598952 · 被引用次数：14 · 研究领域：Organic and Molecular Conductors Research、Magnetism in coordination complexes、Quantum and electron transport phenomena

The molar spin susceptibilities χ(T) of Na-tetracyanoquinodimethane (TCNQ), K-TCNQ, and Rb-TCNQ(II) are fit quantitatively to 450 K in terms of half-filled bands of three one-dimensional Hubbard models with extended interactions using exact results for finite systems. All three models have bond order wave (BOW) and charge density wave (CDW) phases with boundary V = Vc(U) for nearest-neighbor interaction V and on-site repulsion U. At high T, all three salts have regular stacks of \documentclass[12pt]{minimal}\begin{document}$\rm TCNQ^-$\end{document} TCNQ − anion radicals. The χ(T) fits place Na and K in the CDW phase and Rb(II) in the BOW phase with V ≈ Vc. The Na and K salts have dimerized stacks at T < Td while Rb(II) has regular stacks at 100 K. The χ(T) analysis extends to dimerized stacks and to dimerization fluctuations in Rb(II). The three models yield consistent values of U, V, and transfer integrals t for closely related \documentclass[12pt]{minimal}\begin{document}$\rm TCNQ^-$\end{document} TCNQ − stacks. Model parameters based on χ(T) are smaller than those from optical data that in turn are considerably reduced by electronic polarization from quantum chemical calculation of U, V, and t of adjacent \documentclass[12pt]{minimal}\begin{document}$\rm TCNQ^-$\end{document} TCNQ − ions. The χ(T) analysis shows that fully relaxed states have reduced model parameters compared to optical or vibration spectra of dimerized or regular \documentclass[12pt]{minimal}\begi...