Theory of Neutral-lonic Transition in Organic Crystals.I.Monte Carlo Simulation of Modified Hubbard Model

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The one dimensional modified Hubbard model, which is a simplest model showingthe neutral-ionic (Nl) transition, is investigated by the quantum Monte Carlo simula-tion. The physical quantities concerning the ground state (the kinetic energy, thedegree of charge transfer, the probability of the double occupancy), correlation func-Lions and excitation energies (charge transfer gap E.. and magnetic gap E...) arecalculated as functions of the site energy difference A . It is concluded that the modelshows two phases according to A. The tonic phase (J< A.) is characterized by thegapless spin wave which leads to the divergence of the correlation functions in thesame manner as the case of ,4 =0 (the Hubbard model). When A exceeds A., E...starts to rise continuously (neutral phase), while E.. has a minimum around A..Within the statistical accuracy, our simulation does not exclude the appearance of themetallic state at the transition point.
社団法人日本物理学会の論文
1986-08-15