为了高效地控制分子电子学器件的局域磁学性质，实现外电场对金属表面分子自旋自由度的调控是十分必要的。然而，目前电场对分子自旋态的调控机理尚不明确，难以进行理性的材料设计，需要从微观层次进行系统的理论研究。利用第一性原理方法研究磁性分子-表面体系面临的主要挑战是对范德华作用和强关联效应的处理。申请人发现密度泛函理论结合局域Hubbard U修正的DFT+U方法能处理好3d电子的强关联效应，从而能准确地预测分子的自旋态，而计算量却远小于同等精度的杂化泛函。本项目拟实现基于改进的范德华泛函的DFT+U方法，以在同一框架下准确描述范德华作用和强关联效应。接着以吸附在Cu(111)表面的二茂铁(Fc)分子为模型，探索电场对Fc分子自旋态的调控作用，并通过探索电荷转移和Fc分子电子结构的变化阐明调控机理。本研究有望对分子自旋电子学器件的开发提供一定的理论基础。

It is essential to realize the manipulation of the molecular spin degrees of freedom in molecule-on-metal systems with an external electric field (EEF), for an efficient control of the local magnetic properties of molecule-based electronic devices. However, the mechanism of the manipulation of the EEF on the molecular spin states is still not clear, which makes the rational design of the materials rather difficult, such that it is necessary to perform a systematic theoretical study at the microscopic level. The main challenge for first-principles simulations of the magnetic molecule-surface interacting systems, is to deal with the van der Waals (vdW) interaction and the strong correlation effects. We have found that the strong correlation of the 3d electrons can be tackled by the DFT+U approach, which combines density functional theory with the local Hubbard U correction, and thus DFT+U can accurately predict the spin states of molecules, while the computational cost is much lower than that of the hybrid functionals with comparable accuracy. In this study, we will develop the DFT+U approach based on the optimized vdW density functionals, in order to describe the vdW interaction and strong correlation accurately within the same framework. Then we employ the ferrocene (Fc) molecule deposited on the Cu(111) surface as a model system, and explore the modification of the EEF on the spin state of the Fc molecule, and explain the mechanism in terms of the charge transfer and variations of the electronic structure of the Fc molecule. This work will provide a theoretical basis for the development of molecular spintronic devices.