Antiferromagnetic ferromagnetic transition in zigzag graphene nanoribbons induced by substitutional doping

Using first-principles calculations based on density functional theory, we show that the ground state of zigzag-edged graphene nanoribbons(ZGNRs) can be transformed from antiferromagnetic(AFM) order to ferromagnetic(FM) order by changing the substitutional sites of N or B dopants. This AFM–FM transition induced by substitutional sites is found to be a consequence of the competition between the edge and bulk states. The energy sequence of the edge and bulk states near the Fermi level is reversed in the AFM and FM configurations. When the dopant is substituted near the edge of the ribbon, the extra charge from the dopant is energetically favorable to occupy the edge states in AFM configuration. When the dopant is substituted near the center, the extra charge is energetically favorable to occupy the bulk states in FM configuration. Proper substrate with weak interaction is necessary to maintain the magnetic properties of the doped ZGNRs. Our study can serve as a guide to synthesize graphene nanostructures with stable FM order for future applications to spintronic devices.     

Ab initio investigations of the charge transport properties of endohedral M@C20（M=Na and K）metallofullerenes

Using density functional theory and quantum transport calculations based on nonequilibum Green’s function formalism,we investigate the charge transport properties of endohedral M@C 20 (M=Na and K) metallofullerenes.Our results show that the conductance of C 20 fullerene can be obviously improved by insertion of alkali atom at its centre.Both linear and nonlinear sections are found on the I-V curves of the Au-M@C 20-Au two-probe systems.The novel negative differential resistance behaviour is also observed in Na@C 20 molecule but not in K@C 20.     

Adsorption of sodium ions and hydrated sodium ions on a hydrophobic graphite surface via cation-π interactions

Using density functional theory computation, we show that sodium ions and hydrated sodium ions can be strongly adsorbed onto a hydrophobic graphite surface via cation-π interactions. The key to this cation-π interaction is the coupling of the delocalized π states of graphite and the empty orbitals of sodium ions. This finding implies that the property of the graphite surface is extremely dependent on the existence of the ions on the surface, suggesting that the hydrophobic property of the graphite surface may be affected by the existence of the sodium ions.     

Differences in the adsorption of FePc on coinage metal surfaces

A study of the electronic and structural properties of iron phthalocyanine(FePc) molecules adsorbed on coinage metal surfaces Cu(100) and Cu(110) has been conducted by means of density functional theory calculations.The strength of the molecule-substrate interactions is interpreted in terms of the lateral adsorption geometry and the site specific electronic structure of the molecule.In the case of FePc on a(100)-oriented copper surface,the benzopyrrole leg is found to be oriented at an angle of 9° or 3° from the [01-1] substrate direction.Further,an upward bend in the molecular plane ranging from 7° to 10° is also observed;giving an almost buckled shape to the molecule.However,in the case of FePc on Cu(110),neither a bend nor a sizable rotation is observed.From the knowledge of the principle structural and electronic properties,it is concluded that FePc-Cu(100) interaction is relatively stronger than FePc-Cu(110) interaction,which is further evidenced by the charge transfer,work function changes,changes in the shape of the adsorbed molecular orbitals,and the orbital shifts.Furthermore,density of states analysis shows that the valence band level shift is surface-and site-dependent.     

Structures,stabilities,and electronic properties of GaAs tubelike clusters and single-walled GaAs nanotubes

<正>The geometric structures,stabilities,and electronic properties of(GaAs)_n tubelike clusters at up to n=120 and single-walled GaAs nanotubes(GaAsNTs) were studied by density functional theory(DFT) calculations.A family of stable tubelike structures with a Ga-As alternating arrangement were observed when n≥8 and their structural units (four-membered rings and six-membered rings) obey the general developing formula.The average binding energies of the clusters show that the tubelike cluster with eight atoms in the cross section is the most stable cluster.The sizedependent properties of the frontier molecular orbital surfaces explain why the long and stable tubelike clusters can be obtained successfully.They also illustrate the reason why GaAsNTs can be synthesized experimentally.We also found that the single-walled GaAsNTs can be prepared by the proper assembly of tubelike clusters to form semiconductors with large band gaps.     

Probing structural and electronic properties of divalent metal Mgn+1 and SrMgn (n=2–12) clusters and their anions

Divalent metal clusters have received great attention due to the interesting size-induced nonmetal-to-metal transition and fascinating properties dependent on cluster size,shape,and doping.In this work,the combination of the CALYPSO code and density functional theory(DFT)optimization is employed to explore the structural properties of neutral and anionic Mg_n+1 and SrMgn(n=2-12)clusters.The results exhibit that as the atomic number of Mg increases,Sr atoms are more likely to replace Mg atoms located in the skeleton convex cap.By analyzing the binding energy,second-order energy difference and the charge transfer,it can be found the SrMg9 cluster with tower framework presents outstanding stability in a studied size range.Further,bonding characteristic analysis reveals that the stability of SrMg9 can be improved due to the strong s-p interaction among the atomic orbitals of Sr and Mg atoms.     

Structure and electronic structure of S-doped graphitic C₃N₄ investigated by density functional theory

The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers.The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4.The S doptant is prone to substitute the N atom bonded with only two nearest C atoms.The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.     

Structure and electronic structure of S-doped graphitic C3N4 investigated by density functional theory

The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers.The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4.The S doptant is prone to substitute the N atom bonded with only two nearest C atoms.The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.     

Real-space observation on standing configurations of phenylacetylene on Cu(111) by scanning probe microscopy

The adsorption configurations of molecules adsorbed on substrates can significantly affect their physical and chemical properties. A standing configuration can be difficult to determine by traditional techniques, such as scanning tunneling microscopy(STM) due to the superposition of electronic states. In this paper, we report the real-space observation of the standing adsorption configuration of phenylacetylene on Cu(111) by non-contact atomic force microscopy(nc-AFM).Deposition of phenylacetylene at 25 K shows featureless bright spots in STM images. Using nc-AFM, the line features representing the C–H and C–C bonds in benzene rings are evident, which implies a standing adsorption configuration. Further density functional theory(DFT) calculations reveal multiple optimized adsorption configurations with phenylacetylene breaking its acetylenic bond and forming C–Cu bond(s) with the underlying copper atoms, and hence stand on the substrate.By comparing the nc-AFM simulations with the experimental observation, we identify the standing adsorption configuration of phenylacetylene on Cu(111). Our work demonstrates an application of combining nc-AFM measurements and DFT calculations to the study of standing molecules on substrates, which enriches our knowledge of the adsorption behaviors of small molecules on solid surfaces at low temperatures.     

Geometrically induced π-band splitting in graphene superlattices

According to band folding analyses, the graphene superlattices can be differed by whether the Dirac points are folded to Γ point or not. In previous studies, the inversion symmetry preserved defects open bandgap in the former superlattices while they cannot in the latter ones. In this paper, by using density functional theory with generalized gradient approximation, we have carefully studied the electronic properties of the latter graphene superlattices, in which the defects would induce π-band splitting to get the π_a1–π_a2 and π_z1–π_z2 band sets. Based on our detailed studies, such splitting could be attributed to the geometrically induced bond-symmetry breaking. In addition, these band sets could be shifted toward each other by the methodology of strain engineering. A bandgap would be opened once the band sets start to overlap. Then,its gap width could be continuously enlarged by enhancing strain until reaching the maximum value determined by the defect density. These studies contribute to the bandstructure engineering of graphene-based nanomaterials, which would be interesting to call for further investigations on both theory and experiment.     

Study of the Binding Energy of Relativistic Nuclear Matter in the Relativistic σ-ω-π Model

A relativistic σ-ω-π model is proposed to calculate the binding energy of relativistic nuclear matter. We put emphasis on the relativistic particle-hole, delta-hole excitation of pion propagator in nuclear matter. The renormalization of the nucleon self-energy in nuclear matter is made for the pseudo-vector πNN and πNΔ couplings by introducing corresponding form factor and by dispersion relation. We find that the density dependence correction to meson-NN coupling constants is very important to saturate the binding energy of nuclear matter. The density dependence correction to πNN and πNΔ coupling constants has the effect of softening the EOS of nuclear matter.     

The ρ-π Puzzle of J/φ and φ′ Decays

The recent BES Collaboration data on φ →PV, particularly the isospin violating mode φ′ → π^oω^o and finding of a finite number for B(φ′ → K^*OK^O), enable us now to deal more precisely about the challenges to theory concerning this extraordinary and remarkableso-called ρ-π puzzle of J/φ and φ′ decays. In terms of the existing data and deploying the simplest phenomenology, measurement of φ′ → π⁺π^- and whether a finite number for the K^*+K^- mode might require a significantly large accumulation of data remain interesting questions.     

Exploring excited‐state proton transfer mechanism for 9,10‐dihydroxybenzo[h]quinolone

In this work, we mainly focus on the excited‐state intramolecular proton transfer mechanism of a new molecule 9,10‐dihydroxybenzo[h]quinoline (9‐10‐HBQ). Within the framework of density functional theory and time‐dependent density functional theory methods, we have theoretically investigated its excited‐state dynamical process and our theoretical results successfully reappeared previous experimental electronic spectra. The ultrafast excited‐state intramolecular proton transfer process occurs in the first excited state (S₁ state) forming 9‐10‐HBQ‐PT1 structure without potential energy barrier along with hydrogen bond (O₃–H₄···N₅). Then the second proton may transfer via another intramolecular hydrogen bonded wire (O₁–H₂···N₃) with a moderate potential energy barrier (about 7.69 kcal/mol) in the S₁ state forming 9‐10‐HBQ‐PT2 configuration. After completing excited‐state dynamical process, the molecule on the first excited electronic state would come back to the ground state. We not only clarify the excited‐state dynamical process for 9‐10‐HBQ but also put forward new predictions and successfully explain previous experimental results.     

FT‐Raman,IR and UV‐visible spectral investigations and ab initio computations of a nonlinear food dye amaranth

Amaranth (E123, Food Red 9, FD & C Red 2) is a sulfonated azo dye used as a color additive in foodstuffs, pharmaceuticals and cosmetics. FT‐IR and FT‐Raman spectra of amaranth were recorded and analyzed. Density functional theory (DFT) calculations were performed to derive the equilibrium geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The results of the optimized molecular structure gave clear evidence for the intramolecular charge transfer (ICT) and intramolecular hydrogen bonding in the molecule. Azo stretching wavenumbers are lowered owing to conjugation and π‐electron delocalization. Time‐dependent density functional theory (TD‐DFT) calculations of the electronic spectra were performed on the optimized structure and compared with the experimental UV‐visible spectrum. Vibrational spectra, natural bonding orbitals (NBO) analysis and optimized geometry indicate C H·N hydrogen bonding in the molecule. The first hyperpolarizability of the molecule was calculated. The optical nonlinearity of the dye is due to the donation of the electron density from the hydroxyl group of the conjugated system via naphthalene ( 2 ) ring into π*‐orbital of the azo moiety. Copyright © 2008 John Wiley & Sons, Ltd.     

基于密度泛函的茶多酚分子EGCG和GCG的光谱计算

茶多酚是绿茶中主要生化活性成分之一。选取茶多酚中含量较高,同时也是性质较活泼、功效较明显的表没食子儿茶素没食子酸酯（EGCG）及其异构体没食子儿茶素没食子酸酯（GCG）分子做红外光谱和紫外光谱的计算和研究。使用Gaussian软件,采用B3LYP密度泛函理论（DFT）在6-311g(d,p)基组水平上优化其几何构型。频率计算得到红外光谱后,再进行振动特征分析,可以看到在EGCG和GCG的红外光谱图中每个振动模式下所有基团振动的权重,结合谱图做出相应的振动归属和对比分析。发现：两分子红外谱图相似,分别在1 711和1 717 cm-1处为羰基的伸缩振动吸收峰,苯环上酚羟基的伸缩振动吸收峰集中在3 500~3 800 cm-1,1 000～1 600 cm-1的多个峰都有苯环面内弯曲振动参与,在1 350和1 280 cm-1附近吸收峰是亚甲基次甲基面内弯曲振动引起的,在500 cm-1以下吸收峰都为原子的面外弯曲振动。采用固相粉末压片法,使用IRPRESTIGE-21红外光谱仪测量了EGCG分子的红外光谱（400～4 000 cm-1）,对比理论计算的EGCG分子红外光谱各吸收峰位值,发现在固相中实际测得的EGCG分子的红外光谱与气相下的理论计算值基本吻合,理论计算值略微有些红移,原因可能是理论计算在气相条件下采用的势函数存在误差,相比于无分子相互作用力的气相,实际测量固相光谱的分子键强度比气相条件下要略大些。使用Gaussian软件,采用含时密度泛函理论（TD-DFT）,选取乙醇作为溶剂,计算了EGCG分子的15个激发态,分析了激发态的组成和能级跃迁情况。计算所得的2个吸收峰分别位于229.3和276.4 nm处,主要对应p电子与苯环π键上电子形成的p-π共轭的电子跃迁及苯环、杂环上π→π*跃迁。从分析振子强度得知,基态跃迁到S4,S5,S6和S12激发态为产生紫外光谱的主要原因,另外的激发态可能为禁阻跃迁,振子强度均小于0.01。上述计算值与使用UV-6100S型紫外分光光度计所测得的EGCG分子在乙醇溶剂中235.1和278.7 nm的最大吸收峰吻合,计算值略有蓝移,可能是茶多酚提取时或本身就带有弱碱性所致。该研究可为研究EGCG分子和GCG分子的性质和生物活性及茶多酚的抗氧化性提供理论参考。     

CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利，属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV)，表明在较低温度下，CO分子在Pu (100)表面会发生离解吸附，离解的C，O原子将占据能量最低的穴位.     

CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利,属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV),表明在较低温度下,CO分子在Pu (100)表面会发生离解吸附,离解的C,O原子将占据能量最低的穴位. 关键词： 密度泛函理论 Pu (100) CO 分子和离解吸附     

基于石墨烯电极的Co-Salophene分子器件的自旋输运

采用基于非平衡格林函数结合第一性原理的密度泛函理论的计算方法,研究了基于锯齿型石墨纳米带电极的Co-Salophene分子器件的自旋极化输运性质.计算结果表明,当左右电极为平行自旋结构时,自旋向上的电流明显大于自旋向下的电流,自旋向下的电流在[-1V,1V]偏压下接近零,分子器件表现出优异的自旋过滤效应.与此同时,在自旋向上电流中发现负微分电阻效应.当左右电极为反平行自旋结构时,器件表现出双自旋过滤和双自旋分子整流效应.除此之外,整个分子器件还表现出较高的巨磁阻效应.通过分析器件的自旋极化透射谱、局域态密度、电极的能带结构和分子自洽投影哈密顿量,详细解释该分子器件表现出众多特性的内在机理.研究结果对设计多功能分子器件具有重要的借鉴意义.     

基于密度泛函理论的对二甲苯分子电子光谱的外场效应研究

对二甲苯（PX）是化工领域一种非常重要的原料,被广泛地用于香料、医药、油墨和农药等的生产,因此研究PX分子的电子光谱和外场效应,对于它的检测和降解具有十分重要的意义。为研究外电场作用下,PX分子的紫外-可见（UV-Vis）光谱的变化,采用密度泛函理论（density functional theory,DFT）B3LYP方法在6-311++G(d, p)基组水平上,优化了不同外电场（0～0.025 a.u.,0～1.285 6×1010 V·m-1）作用下PX分子的基态几何构型,在此基础上利用含时密度泛函理论（TDDFT）计算了PX分子的UV-Vis吸收光谱,最后对PX分子紫外吸收峰和摩尔吸收系数受外电场作用的的影响规律进行了研究。结果表明：有波长为189 nm、摩尔吸收系数为35 580 L·mol-1·cm-1的强吸收峰,处于E₁带,它是环状共轭的三个乙烯键的苯型体系中的π→π*电子跃迁产生的;与苯分子相比,吸收峰出现11 nm的红移：由于两个甲基和苯环形成p-π共轭,苯环的大π键变弱,故PX分子的紫外吸收峰出现红移;当增加了外电场后,最低未占据轨道(LUMO)向外电场的反方向偏移,导致苯环上的电子密度减小,大π键变弱,π→π*跃迁需要的能量降低,电子跃迁产生的波长增大,吸收峰出现显著红移,当外电场增大到0.020 a.u.时,红移已经非常明显;外电场的引入,导致苯环上的电子密度减小,大π键变弱,π→π*跃迁的电子数减少,摩尔吸收系数降低,随着外电场的增强,摩尔吸收系数降低明显,尤其在外电场增强到0.020a.u.后,摩尔吸收系数降低非常显著。这些工作为PX的检测和降解方法研究提供了一定的理论依据,也对其他有机污染物的检测方法和降解机理的研究有启示作用。     

ab initio Studies on Molecular Conductor (BEDSe-TTF)2[Fe(CN)5NO]

In this paper the ab initio study using pseudopotential plane wave method with the local spin density functional approximation is presented for the molecular conductor (BEDSe-TTF)₂[Fe(CN)₅NO]. The mean electronic density distributions are obtained, and we find that the extended π orbital of the selenium does not affect the properties of material as assumed in other papers and the "side-by-side" type S...S interaction is the primary interaction between donors. From band structure calculations we analyze the influence of the NO groups on the electronic structure and magnetic properties of molecule. It is shown that the itinerant electrons important to electronic properties in these types of hybrids are delocalized electrons contributed by NO groups, instead of by the 3d electrons of Fe. Additionally, we have found that the localized magnetic moment is also contributed by the NO groups in this molecular conductor. From total energy calculations the molecular structure with the lowest energy is found due to the interaction between split spins, and the particular positions of the NO groups are obtained.