基于DFTB法的碳纳米管(CNT )储氢机理的探讨

碳纳米结构材料(C60,CNT)被认为是氢能的主要载体而备受关注,但近几年来的报道不尽一致。基于DFTB分析法,结合相关的研究成果,从氢与碳纳米结构的原子相互作用入手,探讨CNT储氢的可行性,并介绍了氢化的C60-H和CNT-H结构和电化学特性。理论分析表明,H2分子直接穿透碳结构网进入内部(C60笼,碳纳米管)的趋势受到来自碳纳米结构本身势垒的抑制,而通过转换极性,利用电化学的方式储存与释放氢气是可行的。

采用优化的DFTB参数对铜(111)表面碳二聚化的分子动力学研究（英文）

针对铜表面化学反应,我们发展了一套铜-碳体系的密度泛函紧束缚(DFTB)参数。测试结果表明这套参数可以很好的描述吸附铜或碳原子前后铜表面的几何结构和能量。基于这套参数,我们对Cu(111)表面的碳二聚化过程进行了分子模拟研究。即使在高温下,直接的分子动力学模拟也很难观察到碳二聚体的形成。这是因为高温下铜表面显著的结构弛豫一定程度上阻止了二聚化。为了研究高温下铜表面碳二聚化的机理,我们进行了赝动力学模拟。发现在二聚化的过程中,碳原子形成C-Cu-C桥状结构以后,会绕中间Cu原子转动,最后形成碳二聚体。1300 K下碳二聚化的自由能垒约0.9 eV。

Density Functional Based Tight Binding (DFTB) Study on the Thermal Evolution of Amorphous Carbon

Density functional based tight binding (DFTB) model is employed to study the sp3-to-sp2 transformation of diamond-like carbon at elevated temperatures. The understanding could lead to the direct-growth of graphene on a wide variety of substrates.

Molecular Simulations in Materials Science

Molecular simulation finds application in a wide range of research fields based on life and materials sciences.It helps comprehend and predict the chemical and physical properties of substances;thus,it is useful in directing R&D and industrial production.In this special issue,we focus on molecular simulations in material sciences.Molecular simulation employs computational models from microscopic to mesoscopic levels,which is reflected in this special issue.For example,Liu et al.1 reported modulation of catalytic activity for CO2 hydrogenation using quantum density functional theory(DFT).Yin et al.2 parameterized a semiempirical density functional tight-binding(DFTB)model to study deposition of carbon on copper surface.At the atomic level,Ren et al.

理论研究应变调控硅纳米管的稳定性和带隙

采用SCC-DFTB方法,研究了不同手性参数的单臂硅纳米管在不同拉伸应变作用下的稳定性和带隙变化。结果表明,随着拉伸应力的增加,不同孔径的硅纳米管的形成能都增大,稳定性降低。当拉伸应变大于6%时,表现出较明显的尺寸效应,大孔径的硅纳米管相对不容易被拉伸。当拉伸应变小于4%时,不同孔径的硅纳米管的带隙总体都会增大,然后随着拉伸应变的增加,带隙逐渐变小,当拉伸应变大于9%之后,则变成了金属。拟合得到了不同孔径和应变下硅纳米管的带隙变化分布图,为实验上制备不同的应变和不同的孔径纳米管,进行带隙调控提供一定的理论参考。

First principles study of field effect device through van der Waals and lateral heterostructures of graphene, phosphorene and graphane

Chemical modification and vertical stacking of two-dimensional materials are promising techniques for new nanoelectronic devices. We present Density Functional Tight Binding(DFTB) calculations of a field-effect device,based on lateral and vertical heterostructures of 2D materials. The device consists of a phosphorene channel protected by graphene sheets, which work as contacts and are divided into the source and drain by local hydrogenation of graphene, which gives insulating graphane. In this device composed of only 3 layers, single sheets of graphene-graphane can work as both leads and oxide gate, while also acting as protective layers for a phosphorene channel. We show how for perfect vd W heterostructures of graphane/phosphorene/graphane and graphene/phosphorene/graphene the Schottky barrier is deeply influenced by normal electric fields, and we characterize electronic transport of such a device. Finally, we characterize phosphorene channel doping and defects, which, at very high densities in the transport direction, enables transport inside the phosphorene bandgap.

基于改进ReaxFF力场的全氟己酮热分解机理研究

采用基于密度泛函的紧束缚模型(DFTB)和改进的反作用力场(ReaxFF)对全氟己酮的热分解机理进行反应分子动力学仿真研究,分析了热分解的初始反应路径、微观反应过程以及体系内气体的生成机理,探讨了温度对全氟己酮热分解的影响,建立了以仿真数据为基础的一级动力学方程并对热分解过程进行一级动力学评估。结果表明,全氟己酮热分解的起始反应为:全氟己酮→全氟异戊烷+一氧化碳,全氟己酮热分解的主要产物为一氧化碳、四氟甲烷、六氟丙烯、全氟异丁烯、十氟丁烷、全氟异戊烷及大量活性基团。经一级动力学评估得到指前因子和表观活化能分别为5.0217×1014s-1和1771.96 kJ/mol。

Interaction of Boron-Nitrogen Substitued Graphene Nanoribbon with Nucleobases: The Idea of Biosensor

In this paper we have designed a biosensor device built from B-N substituted graphene nanoribbon within density functional based tight-binding (DFTB) framework. We have investigated the interaction of the nucleobases adenine (A), Guanine (G), Cytosine (C) and Thymine (T) with device. Our calculation suggests that all the nucleobases have different interaction strength when they interact with device and shows that guanine has stronger interaction with device than other nucleobases. It reveals that the absorption energy shows the hierarchy: G > C > T > A. Our results also demonstrate the transport properties of the device and how the transport properties change due to the absorption of nucleobases on the device.

Si-P掺杂石墨烯的稳定性和能带结构的理论研究

采用基于紧束缚密度泛函的计算方法,研究比较了Si掺杂、P掺杂、Si-P掺杂石墨烯的稳定性和能带结构。在Si和P掺杂的石墨烯体系中,发现在掺杂元素方面,Si掺杂石墨烯比P掺杂石墨烯稳定;在掺杂方式方面,高对称性的对位掺杂石墨烯结构的形成能较低,比较稳定。Si掺杂石墨烯的能带结构在G点产生了约0.1 eV的带隙,从良导体过渡到了半导体。在P或Si-P掺杂石墨烯体系中,费米能级上升而穿过价带,使掺杂系统保持金属性。态密度计算表明,P或Si-P掺杂石墨烯体系中费米能级附近主要由P原子的3p态电子和C原子的2p态电子占据,主要的电子性质与P的3p轨道和C的2p轨道相互作用有关。

Efficient predictions of formation energies and convex hulls from density functional tight binding calculations

Defects in materials significantly alter their electronic and structural properties,which affect the per-formance of electronic devices,structural alloys,and functional materials.However,calculating all the possible defects in complex materials with conventional Density Functional Theory(DFT)can be compu-tationally prohibitive.To enhance the efficiency of these calculations,we interfaced Density Functional Tight Binding(DFTB)with the Clusters Approach to Statistical Mechanics(CASM)software package for the first time.Using SiC and ZnO as representative examples,we show that DFTB gives accurate results and can be used as an efficient computational approach for calculating and pre-screening formation ener-gies/convex hulls.Our DFTB+CASM implementation allows for an efficient exploration(up to an order of magnitude faster than DFT)of formation energies and convex hulls,which researchers can use to probe other complex systems.

Thermal bridging of graphene nanosheets via covalent molecular junctions: A non-equilibrium Green's functions-density functional tightbinding study

Despite the uniquely high thermal conductivity of graphene is well known,the exploitation of graphene into thermally conductive nanomaterials and devices is limited by the inefficiency of thermal contacts between the individual nanosheets.A fascinating yet experimentally challenging route to enhance thermal conductance at contacts between graphene nanosheets is through molecular junctions,allowing covalently connecting nanosheets,otherwise interacting only via weak Van der Waals forces.Beside the bare existence of covalent connections,the choice of molecular structures to be used as thermal junctions should be guided by their vibrational properties,in terms of phonon transfer through the molecular junction.In this paper,density functional tight-binding combined with Green's functions formalism was applied for the calculation of thermal conductance and phonon spectra of several different aliphatic and aromatic molecular junctions between graphene nanosheets.Effects of molecular junction length,conformation,and aromaticity were studied in detail and correlated with phonon tunnelling spectra.The theoretical insight provided by this work can guide future experimental studies to select suitable molecular junctions,in order to enhance the thermal transport by suppressing the interfacial thermal resistances.This is attractive for various systems,including graphene nanopapers and graphene polymer nanocomposites,as well as related devices.In a broader view,the possibility to design molecular junctions to control phonon transport currently appears as an efficient way to produce phononic devices and controlling heat management in nanostructures.

DFT study on the interaction of HCHO molecule with S-doped TiO_(2) (001) surface without and with water and oxygen molecules

The interactions of formaldehyde(HCHO)molecule with S-doped anatase TiO_(2)(001)surface without and with water and oxygen were studied by density functional theory(DFT).The adsorption energy of HCHO adsorption on S-doped TiO_(2) surface with water and oxygen(-709.62 kJ/mol)is much larger than that without water and oxygen(-312.14 kJ/mol).For HCHO adsorption system without water and oxygen,one CeH bond of HCHO molecule is broken.The oxygen and carbon atoms of HCHO are bonded to the titanium and sulfur atoms of SeTiO_(2) surface,respectively,and form a CH_(2)OS structure.For the system with water and oxygen,H_(2)O and HCHO molecules are both dissociated.HCHO molecule not only interacts with TiO_(2) surface,but also combines with O_(2) molecule.Two CeH bonds of HCHO are broken,one hydrogen atom(H1)is bonded to the sulfur atom(S)of TiO_(2) surface doping,while another hydrogen atom(H_(2))is bonded to the O atom(O_(2))of O_(2) molecule.The remaining CeO bond can be oxidized to form CO_(2) in subsequent action by oxygen from the atmosphere.The surface doping of sulfur have significant impact on the degradation of HCHO molecule on anatase TiO_(2)(001)surface with H_(2)O and O_(2).

几何限制对碳纳米管中气体小分子吸附与分离的影响

使用DFTB方法研究多种单壁碳纳米管(SWCNTs)的应力-应变关系,预测了在几何限制作用下,其杨氏模量和能带结构的变化规律.系统探讨了外部应力作用下SWCNTs内外表面吸附H_2,N_2和H_2S气体分子能力的变化规律,确定了SWCNTs对于上述混合气体的分离和提纯能力.

Toward molecular models of proton pumping：Challenges,methods and relevant applications

Motivated by several long-lasting mechanistic questions for biomolecular proton pumps,we have engaged in developing hybrid quantum mechanical/molecular mechanical(QM/MM) methods that allow an efficient and reliable description of long-range proton transport in transmembrane proteins.In this review,we briefly discuss several relevant issues:the need to develop a "multi-scale" generalized solvent boundary potential(GSBP) for the analysis of chemical events in large trans-membrane proteins,approaches to validate such a protocol,and the importance of improving the flexibility of QM/MM Hamiltonian.Several recent studies of model and realistic protein systems are also discussed to help put the discussions into context.Collectively,these studies suggest that the QM/MM-GSBP framework based on an approximate density functional theory(SCC-DFTB) as QM holds the promise to strike the proper balance between computational efficiency,accuracy and generality.With additional improvements in the methodology and recent developments by others,especially powerful sampling techniques,this "multi-scale" framework will be able to help unlock the secrets of proton pumps and other biomolecular machines.