平面芳香分子的集体自旋和电荷激发
Collective Spin and Charge Excitations in Planar Aromatic Molecules
摘要：
采用高精度的固定节点扩散蒙特卡罗（DMC）方法，计算了一系列电荷中性平面非梯形芳香族化合物的最低三重态集体激发（自旋能隙）和单重态激发（电荷能隙）的上限.两个激发能都低于从Hartree-Fock轨道得到的粒子-空穴激发能的连续谱。因此，它们可以被解释为粒子-空穴通道中真正的束缚态。假设最近提出的$sp^2$键合体系的共振价键（RVB）基态[ M. Marchi，{ \em et. al.}，物理修订版信函{ \bf 107}，086807（2011）]提供了作为两个自旋和双光子-holon束缚态的两种激发态的统一描述。我们证实了我们的解释，通过精确对角化研究有限蜂窝集群上的极小模型。
英文摘要：
Employing high accuracy fixed node diffusion Monte Carlo (DMC) method we calculated the lowest triplet collective excitation (spin gap), as well as an upper bound for the singlet excitations (charge gap) in a series of charge neutral planar non-ladder aromatic compounds. Both excitation energies lie below the continuum of particle-hole excitation energies obtained from Hartree-Fock orbitals. Hence they can be interpreted as genuine bound states in the particle-hole channel. Assuming a resonating valence bond (RVB) ground state which has been recently suggested for $sp^2$ bonded systems [ M. Marchi, {\em et. al.}, Phys. Rev. Lett. {\bf 107}, 086807 (2011)], offers a unified description of both excited states as two-spinon and doublon-holon bound states. We corroborate our interpretation, by Exact diagonalization study of a minimal model on finite honeycomb clusters.
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