25 research outputs found
Ab initio derivation of multi-orbital extended Hubbard model for molecular crystals
From configuration interaction (CI) ab initio calculations, we derive an
effective two-orbital extended Hubbard model based on the gerade (g) and
ungerade (u) molecular orbitals (MOs) of the charge-transfer molecular
conductor (TTM-TTP)I_3 and the single-component molecular conductor
[Au(tmdt)_2]. First, by focusing on the isolated molecule, we determine the
parameters for the model Hamiltonian so as to reproduce the CI Hamiltonian
matrix. Next, we extend the analysis to two neighboring molecule pairs in the
crystal and we perform similar calculations to evaluate the inter-molecular
interactions. From the resulting tight-binding parameters, we analyze the band
structure to confirm that two bands overlap and mix in together, supporting the
multi-band feature. Furthermore, using a fragment decomposition, we derive the
effective model based on the fragment MOs and show that the staking TTM-TTP
molecules can be described by the zig-zag two-leg ladder with the
inter-molecular transfer integral being larger than the intra-fragment transfer
integral within the molecule. The inter-site interactions between the fragments
follow a Coulomb law, supporting the fragment decomposition strategy.Comment: 16 pages, 8 figures, published versio
Research and Design of a Routing Protocol in Large-Scale Wireless Sensor Networks
无线传感器网络,作为全球未来十大技术之一,集成了传感器技术、嵌入式计算技术、分布式信息处理和自组织网技术,可实时感知、采集、处理、传输网络分布区域内的各种信息数据,在军事国防、生物医疗、环境监测、抢险救灾、防恐反恐、危险区域远程控制等领域具有十分广阔的应用前景。 本文研究分析了无线传感器网络的已有路由协议,并针对大规模的无线传感器网络设计了一种树状路由协议,它根据节点地址信息来形成路由,从而简化了复杂繁冗的路由表查找和维护,节省了不必要的开销,提高了路由效率,实现了快速有效的数据传输。 为支持此路由协议本文提出了一种自适应动态地址分配算——ADAR(AdaptiveDynamicAddre...As one of the ten high technologies in the future, wireless sensor network, which is the integration of micro-sensors, embedded computing, modern network and Ad Hoc technologies, can apperceive, collect, process and transmit various information data within the region. It can be used in military defense, biomedical, environmental monitoring, disaster relief, counter-terrorism, remote control of haz...学位:工学硕士院系专业:信息科学与技术学院通信工程系_通信与信息系统学号:2332007115216
Optical Conductivity in a Two-Dimensional Extended Hubbard Model for an Organic Dirac Electron System α-(BEDT-TTF)2I3
The optical conductivity in the charge order phase is calculated in the two-dimensional extended Hubbard model describing an organic Dirac electron system α -(BEDT-TTF) 2 I 3 using the mean field theory and the Nakano-Kubo formula. Because the interband excitation is characteristic in a two-dimensional Dirac electron system, a peak structure is found above the charge order gap. It is shown that the peak structure originates from the Van Hove singularities of the conduction and valence bands, where those singularities are located at a saddle point between two Dirac cones in momentum space. The frequency of the peak structure exhibits drastic change in the vicinity of the charge order transition