TTF-CA有机分子晶体多铁性的数值研究

基于一维派尔斯-哈伯德模型,采用数值精确对角化和约束路径量子蒙特卡罗数值方法,研究有机分子晶体TTF-CA（tetrathiafulvalene-p-chloranil）的多铁性特征.当填充电子数与格点数相等时（即半填充）,两种方法的计算结果表明,在一定的参数空间体系存在反铁磁和铁电极化共存的多铁状态.在弱电子关联区间,数值计算结果与哈特利-福克平均场得到的结果一致.但在中等至强电子关联区间,数值结果预言,多铁性产生的电声子相互作用强度远低于平均场给出的结果.当填充电子数略低于格点数时,体系存在铁磁与铁电极化共存的状态.研究结果有助于理解和设计新型有机多铁性材料.

Numerical study of multiferroicity in the TTF-CA organic molecular crystal

Based on the one-dimensional Peierls-Hubbard model,the multiferroicity of the TTF-CA organic molecular crystal was studied by using numerical exact diagonalization and constrained-path Monte Carlo methods.At half filling,the calculated results from both numerical methods showed that there existed antiferromagnetism and ferroelectricity in a certain parameter regime.At weak electron correlation,the numerical results were in agreement with the results obtained from Hartree-Fock mean field theory.However,at intermediate and strong electron correlations,the electron-phonon coupling for producing multiferroicity predicted from numerical study was much smaller than the one from mean field prediction.Away from half filling,it existed ferromagnetism and ferroelectricity.The numerical results were useful for understanding and designing novel organic multiferroic materials.