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从离散的SSH模型出发,考虑了链内的电子相互作用,以及由杂质和周围链上的荷电孤子产生的库仑势的影响,探讨了各种掺杂浓度的反式聚乙炔中孤子晶格的能谱与电子束缚态。计算结果表明:在孤子晶格的能谱中,在价带底有两条定域能级,在导带顶存在着多个电子束缚态,随掺杂浓度的升高,束缚态的局域性减弱,禁带中的孤子能级形成孤子能带。当掺杂浓度高达16.67%时,所有的电子束缚态都消失,转变为扩展态。孤子晶格的禁带宽度随着掺杂浓度的增加而增大,最高占据态与导带底之间的能隙则随之逐渐减小。孤子能带底与价带顶之间的能隙在临界浓度附近有一极大值。还讨论了电子-电子相互作用对孤子晶格能谱的影响。
关键词: 相似文献
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苯环取代聚乙炔是一类具有简并基态的发光聚合物.利用扩展的SuSchriefferHeeger模型,研究了这类聚合物链中的孤子、极化子等元激发特性.结果表明:由于苯环与聚乙炔主链间的强π电子耦合,苯环取代抑制了聚乙炔主链的二聚化,减小了导带与价带之间的能隙;因此取代聚乙炔中的元激发具有较小的激发能,同时具有更大的相干长度.尽管苯基取代对元激发有很大的影响,但是非取代聚乙炔中元激发的基本物理规律依然成立,表明这些元激发的基本特性不受取代基团的影响
关键词:
孤子
极化子
苯基取代聚乙炔 相似文献
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本文在苏武沛、Schrieffer和Heeger(SSH)模型的基础上,分别考虑site-type杂质势和Hubbard电子强关联的作用,计算了反式聚乙炔链的电子能谱、本征矢和序参量。结果发现,杂质势对孤子有较强的钉扎作用,它破坏了电子能谱对称性,并使midgap态发生移动,这与Hubbard电子强关联对孤子能级的影响根本不同。值得指出的是,只有同时考虑site-type杂质势和Hubbard相互作用,才能对聚乙炔的掺杂光吸收实验做出正确的理论解释。 相似文献
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在均匀电子气模型下,通过求解Dirac方程,计算了类氢离子束缚态能级能量与等离子体密度的关系,得到了能近似估算能级能量随等离子体密度变化的新拟合公式,该公式同样可以用以估算不同束缚态能级发生压致电离时的临界电子密度.通过与自洽场离子球模型计算结果的比较,作为一种简单和快捷的计算方法,均匀电子汽模型在近似计算束缚态能级能量及压致电离临界电子密度方面是自洽场离子球模型得很好近似方法. 相似文献
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《Current Applied Physics》2015,15(11):1417-1420
By using first-principles calculations within the density functional theory and the many-body perturbation theory, we investigate the structural, electronic, and optical properties of bulk Cu2Se with a recently discovered low-temperature layered configuration. We demonstrate that the effects of the van der Waals forces significantly modify the interlayer binding and distance in the layered Cu2Se, while the band gap is invariant. Our density functional theory and post-processing GW calculations reveal that for the layered structure, GW correction remedies the serious band-gap underestimation of the density functional theory from 0.12 eV to 0.99 eV. By solving the Bethe–Salpeter equation, we find that the optical gap of the layered Cu2Se is 0.86 eV, which is in close agreement with previous experimental observations. In addition, we show that the high-temperature fluorite structure has no band gap, even after GW correction, explaining that the band gap controversy among the theories stems from different structural models. This work may serve as an important guide in designing and evaluating photovoltaic devices using Cu2Se-based materials. 相似文献
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Yu. G. Korobova D. I. Bazhanov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2013,7(3):479-484
Our theoretical studies using methods of electron density functional theory show that hydrogen, fluorine, and oxygen impurities must be present in the chamber during the synthesis of linear-chain carbon to form and stabilize experimentally observed kinks in carbon chains. The kink in the carbon chain forms during the adsorption of impurity atoms onto the chain. It is shown that it is energetically advantageous for impurity atoms to form kinks rather than to occupy other adsorption positions. The optimal kink angle of carbon chains is determined. The stability of bent carbon chains is estimated as a function of the length of linear fragments. It is shown that the formation of kinks leads to that the formation of a narrow band gap near the Fermi level: E gH = 0.56 eV, E gF = 0.59 eV, and E gO = 1.04 eV. 相似文献
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M.R Manaa 《Solid State Communications》2004,129(6):379-383
I report electronic structures and the cohesive energy for face-centered-cubic (fcc) solid C48N12 using generalized-gradient density-functional theory. The full vibrational spectrum of the C48N12 cluster is calculated within the harmonic approximation at the B3LYP/6-31G* level of theory. The results show that fcc is energetically preferred and a more stable crystal form than body-centered-cubic (bcc). C48N12 clusters are found to condense by a weak (0.29 eV) van der Waals force. The band gap of fcc C48N12 is calculated to be 1.3 eV at the GGA-PW91 level, whereas the HOMO-LUMO gap is calculated to be 2.74 eV using B3LYP/6-31G*. 相似文献
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In the alkali-metal doped C60, the charge transfer induces the distortion of the bond structure and forms the self-trapping electronic bound states. Our theory manifests: 1, the charge transfer reduces the symmetry of C60 from Ih to D5d. 2, Both the bond distortion and the self-trapping states possess layer structures and are localized in the equatorial area. 3, The carbon atoms in charged C60 are divided into eight layers with an inversion center, then there exist four nonequivalent groups of carbon atoms. It makes the NMR line split into a fine structure with strength ratio 1:1:2:2. 4, The charged C60 has two self-trapping bound states, one is 0.06eV above HOMO with odd parity and the other is 0.05 eV below LUMO with even parity. 相似文献
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Shuhui Lv Hongping Li Deming HanZhijian Wu Xiaojuan Liu Jian Meng 《Journal of magnetism and magnetic materials》2011,323(5):416-421
Electronic structure calculations based on density functional theory (DFT) within the generalized gradient approximation (GGA) and GGA+U for manganite cuprate compound LuCu3Mn4O12 have been performed, using the full-potential linearized augmented plane wave method. The calculated results indicate that LuCu3Mn4O12 is ferrimagnetic and half-metallic in both GGA and GGA+U calculations. The minority-spin band gap is 0.7 eV within GGA, which is larger than that of LaCu3Mn4O12 (0.3 eV), indicating its better half-metallicity. Further, the minority-spin gap enlarges from 0.7 to 2.8 eV with U taken into account, and simultaneously the Fermi level being shifted to the middle of the gap, making the half-metallic energy gap to be 1.21 eV. These results demonstrate that electronic correlation effect enhances the stability of half-metallic property. These facts make this system interesting candidates for applications in spintronic devices. 相似文献
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Vanessa Cristina de Medeiros Railton Barbosa de Andrade Glauco Favilla Bauerfeldt 《Molecular physics》2018,116(17):2187-2195
Highly correlated calculations at the multi-reference configuration interaction levels including singles and doubles excitations (MR-CISD) and extensivity corrections (MR-CISD?+?Q) have been performed to study some low-lying valence and Rydberg states of the CF3 radical. Our highest level results (at the MR-CISD?+?Q level) yield the following energy ordering: 3s (7.90?eV)?12A2 (8.61?eV)?3pπ (8.72?eV)?3pz (8.73?eV). MR-CISD results indicate transitions of similar intensities from the ground to the following three final states, in the following order: 3pπ?>?3pz?>?3s. It has also been found that the aforementioned Rydberg states should be responsible for visible emissions and correspond to transitions between bound states. Therefore, it is suggested that the lack of vibrational structure in the visible band of parent systems (e.g. CF3Cl) may be due to a transition from a bound to an unbound state of the parent molecule. 相似文献
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The electronic structure of silicon carbide with increasing germanium content have been examined using first principles calculations based on density functional theory. The structural stability is analysed between two different phases, namely, cubic zinc blende and hexagonal phases. The zinc blende structure is found to be the stable one for all the Si1-xGexC semiconducting carbides at normal pressure. Effect of substitution of Ge for Si in SiC on electronic and mechanical properties is studied. It is observed that cubic SiC is a semiconductor with the band gap value 1.243?eV. The band gap value of SiC is increased due to the substitution of Ge and the band gap values of Si 0.75 Ge 0.25 C, Si 0.50 Ge 0.50 C, Si 0.25 Ge 0.75 C and GeC are 1.322 eV, 1.413 eV, 1.574 eV and 1.657?eV respectively. As the pressure is increased, it is found that the energy gap gets decreased for Si1-x GexC (X?=?0, 0.25, 0.50, 0.75, 1). The elastic constants satisfy the Born – Huang elastic stability criteria. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also calculated and compared with the other available results. 相似文献
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采用基于密度泛函理论的广义梯度近似,对C60富勒烯-巴比妥酸及其二聚体的几何结构和电子结构进行了计算研究.发现:C60富勒烯-巴比妥酸只有一种稳定结构,且掺杂巴比妥酸基团对C60分子构型的影响是局域的.C60富勒烯-巴比妥酸的二聚体有三种同素异构体,分别以[6,5]—[6,5],[6,6]—[6,5]和[6,6]—[6,6]三种方式键合,从能隙大小顺序和总能相对大小来看,[6,6]—[6,6]结构最为稳定.电子结构方面,在C60富勒烯-巴比妥酸单体中,Donor-Acceptor电荷转移体系为C60富勒烯-巴比妥酸,即电荷是从C60向巴比妥酸转移.由前线轨道和自旋布居数得知,C60富勒烯-巴比妥酸单体很好地保留了C60的电磁性质,但稳定性下降,易发生二次加成反应形成二聚体.对于C60富勒烯-巴比妥酸二聚体,Mulliken电荷分析显示,在加成四元环处的碳原子分别得到0104e和0106e电荷,而与它们邻近的碳原子则失去电子,带有正电荷,且距加成位置越近的碳原子失去的电荷越多.在远离加成位置处,碳原子的净电荷变化相对较小.与单体152eV能隙相比,二聚体中的能隙为1.45eV.其前线轨道分布与单体相比,最高占据轨道几乎未变,但最低未占据轨道发生了很大变化.
关键词:
几何结构
电子结构
密度泛函 相似文献
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Abdelaziz M. Ibraheem Mohammed A.H. Khalafalla Mohamed H. Eisa 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(3):42
We report on the first principle density functional calculation of the charge transition levels of native defects (vacancies and interstitials) in CaF2 structure. The transition level was defined as the Fermi level where two charge states of given defect have the same formation energy. The common error in the band gap inherited to semiclocal density functional has been accounted for by incorporating the hybrid density functional method, leading to correct placement of the transition levels within the band gap. The band gap size from hybrid calculation has been validated using the full potential, Linearized Augmented Planewave method with the Modified-Becke-Johnson exchange potential. Prior to level calculations, we ensured that an agreement between the formation energies from small (95–97 atoms) and large (323–325 atoms) supercells was achieved after applying the Makov-Payne correction method. Our calculated transition level for the anion vacancy was 2.97 eV below the conduction band, agreeing with the experimental optical absorption band at 3.3 eV associated with the electron transition from the ground state F-center to the conduction band in CaF2. 相似文献
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Cd1-x ZnxS nanocrystals are prepared by a co-precipitation method with different atomic fractions of Zn.The texture,structural transformation and optical properties with increasing x value in Cd1-x ZnxS are studied with scanning electron microscopy,electron diffraction patterning,and absorption spectra respectively.Quantum confinement in a strained CdS/Cd1-xZnxS related nanodot with various Zn content values is investigated theoretically.Binding energies on exciton bound CdS/CdxZn1-xS quantum dot are computed,with consideration of the internal electric field induced by the spontaneous and piezoelectric polarizations,and thereby the interband emission energy is calculated as a function of the dot radius.The optical band gap from the UV absorption spectrum is compared with the interband emission energy computed theoretically.Our results show that the average diameter of composite nanoparticles ranges from 3 nm to 6 nm.The X-ray diffraction pattern shows that all the peaks shift towards the higher diffracting angles with an increase in Zn content.The lattice constant gradually decreases as the Zn content increases.The strong absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as the Zn content increases.The values of the absorption edge are found to shift towards the shorter wave length region and hence the direct band gap energy varies from 2.5 eV for the CdS film and 3.5 eV for the ZnS film.Our numerical results are in good agreement with the experimental results. 相似文献