University of Groningen, Nijenborgh 4, Groningen 9747AG, The Netherlands.
Phys Chem Chem Phys. 2011 Jan 7;13(1):144-8. doi: 10.1039/c0cp01310b. Epub 2010 Oct 29.
Magnetic properties of the TTF-CA molecular crystal below the neutral to ionic transition temperature are studied using the embedded cluster approach in combination with density functional theory. The calculated values of the Heisenberg exchange integral between the neighboring TTF and CA molecules stacked along the crystallographic axis a suggest that the ionic phase of the TTF-CA can be described as an alternating antiferromagnetic spin-1/2 Heisenberg chain with the exchange integral J = 1124 cm(-1) and the alternation parameter δ = 0.46. Although the combination of ferroelectricity of the ionic phase with the antiferromagnetic ordering renders TTF-CA multiferroic (as predicted theoretically in G. Giovannetti et al., Phys. Rev. Lett., 2009, 103, 266401), the large value of the alternation parameter should result in a nonmagnetic ground state of this phase. The dependence of the magnetic coupling parameters on the crystal structure is studied and the implications for experimental observation of magnetic properties of TTF-CA are discussed.
采用嵌入簇方法结合密度泛函理论研究了中性到离子转变温度以下 TTF-CA 分子晶体的磁性。计算得到的沿晶体学轴 a 堆积的相邻 TTF 和 CA 分子之间的海森堡交换积分的数值表明，TTF-CA 的离子相可以被描述为具有交换积分 J = 1124 cm(-1)和交替参数 δ = 0.46 的交替反铁磁自旋 1/2 海森堡链。尽管离子相的铁电性与反铁磁有序结合使 TTF-CA 成为多铁性材料（如 G. Giovannetti 等人在 2009 年的 Phys. Rev. Lett.，103，266401 中预测），但交替参数的大值应该导致该相的非磁性基态。研究了磁性耦合参数对晶体结构的依赖性，并讨论了对 TTF-CA 磁性实验观测的影响。
