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arXiv 0810.5452cond-mat.str-elcond-mat.supr-con
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BEDT-TTF盐的哈伯德模型参数化:孤立分子的密度泛函研究

Towards the parameterisation of the Hubbard model for salts of BEDT-TTF: A density functional study of isolated molecules

Edan Scriven, B. J. Powell

摘要:

我们计算了电子/空穴,U,和网站之间的有效库仑排斥能量为一个孤立的BEDT-TTF [双(亚乙基二硫代)四硫富瓦烯]分子在真空中。U=4.2 \pm 0.1 eV的44个实验几何形状取自广泛的构象,多晶型物,阴离子,温度和压力(引用的“误差”是一个标准偏差)。因此,我们得出结论,U基本上是相同的所有研究的化合物。这表明,在BEDT-TTF盐的相图中观察到的强(流体静力学和化学)压力依赖性不是由于U。因此,如果哈伯德模型足以描述BEDT-TTF盐的相图,则由于分子与可极化晶体环境的相互作用,必须存在对哈密顿量中的分子内项的显著压力依赖性和/或哈伯德U的减少。U的重整化值明显小于库仑积分的裸值:在同一组几何结构中,F_0=5.2 \pm 0.1 eV,强调了使用U的重整化值的重要性。位置能量(对于空穴),xi=5.0 \pm 0.2 eV,在同一组几何结构中变化仅比U多一点。然而,我们认为,这起着关键作用,在理解的作用,ET盐的无序一般,并在解释之间的差异,β_L和β_H相的β-(BEDT-TTF)_2I_3特别是。

英文摘要:

We calculate the effective Coulomb repulsion between electrons/holes, U, and site energy for an isolated BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene] molecule in vacuo. U=4.2 \pm 0.1 eV for 44 experimental geometries taken from a broad range of conformations, polymorphs, anions, temperatures, and pressures (the quoted `error' is one standard deviation). Hence we conclude that U is essentially the same for all of the compounds studied. This shows that the strong (hydrostatic and chemical) pressure dependence observed in the phase diagrams of the BEDT-TTF salts is not due to U. Therefore, if the Hubbard model is sufficient to describe the phase diagram of the BEDT-TTF salts there must be significant pressure dependence on the intramolecular terms in the Hamiltonian and/or the reduction of the Hubbard U due to the interaction of the molecule with the polarisable crystal environment. The renormalised value of U is significantly smaller than the bare value of the Coulomb integral: F_0=5.2\pm0.1 eV across the same set of geometries, emphasising the importance of using the renormalised value of U. The site energy (for holes), xi=5.0\pm0.2 eV, varies only a little more than U across the same set of geometries. However, we argue that this plays a key role in understanding the role of disorder in ET salts in general and in explaining the difference between the beta_L and beta_H phases of beta-(BEDT-TTF)_2I_3 in particular.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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