Theory of Neutral-Ionic Transition in Organic Crystals. I. Monte Carlo Simulation of Modified Hubbard Model
Theory of Neutral-Ionic Transition in Organic Crystals. I. Monte Carlo Simulation of Modified Hubbard Model
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DOI：
10.1143/jpsj.55.2735
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发表时间：
1986-08
影响因子：
1.7
通讯作者：
N. Nagaosa;J. Takimoto
中科院分区：
文献类型：
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作者：
N. Nagaosa;J. Takimoto
利用量子蒙特卡罗模拟研究了中性离子跃迁最简单的一维修正Hubbard模型。有关基态的物理量（动能、电荷转移程度、双占据概率）、相关函数和激发能（电荷转移隙E CT和磁隙E MAC）作为位能差的函数Δ计算。根据Δ得出该模型表现为两个阶段。离子相（Δ<Δ c）的特征是无间隙的自旋波导致相关函数发散，其方式与Δ=0 （Hubbard模型）的情况相同。当Δ超过Δ c时，E MAG开始持续上升（中性期），而E CT在Δ c左右出现最小值。在统计精度范围内，我们的模拟没有排除金属态在过渡点的出现。
The one dimensional modified Hubbard model, which is a simplest model showing the neutral-ionic (NI) transition, is investigated by the quantum Monte Carlo simulation. The physical quantities concerning the ground state (the kinetic energy, the degree of charge transfer, the probability of the double occupancy), correlation functions and excitation energies (charge transfer gap E CT and magnetic gap E MAC ) are calculated as functions of the site energy difference Δ . It is concluded that the model shows two phases according to Δ. The ionic phase (Δ<Δ c ) is characterized by the gapless spin wave which leads to the divergence of the correlation functions in the same manner as the case of Δ=0 (the Hubbard model). When Δ exceeds Δ c , E MAG starts to rise continuously (neutral phase), while E CT has a minimum around Δ c . Within the statistical accuracy, our simulation does not exclude the appearance of the metallic state at the transition point.