LiF-CrF3二元系的热力学模拟

采用相图计算(CALPHAD)技术对LiF-CrF3体系进行了相图的优化计算.对液相分别采用置换熔体模型与缔合物模型进行描述,中间化合物Li3CrF6则采用准化学计量比化合物模型描述.模型参数的优化选取实验相平衡数据及第一性原理预测的数据,优化结果表明,缔合物模型比置换熔体模型更能准确地描述液相的实验相平衡数据.     

First-principle calculation for the phonon structure on iron-based superconductors

We perform first-principle phonon calculations for three typical iron-based superconductors, i.e., LaFeAsO,BaFe₂As₂, and FeSe. Though those crystals have different structures, we find that the optical modes associated with Fe vibration have almost similar characters. Moreover, we examine the pressure effect on phonons in FeSe. By increasing the external pressure, the phonon mode frequency related to Fe vibration effectively rises up and the electronic density of states at Fermi level also increases. These results may correlate to the critical temperature enhancement under high pressure.     

First-principle calculations of dilute nitride GaP1−xNx alloy in zinc-blende structures

First-principle plane-wave pseudopotential calculations using the density-functional theory within the local density approximation (LDA) have been carried out to investigate the structural, electronic and thermodynamic properties of zinc-blende dilute nitride GaP_1−xN_x alloy. We have found that the unit cell volumes of GaP_1−xN_x alloys are smaller than the value calculated from the linear interpolation of GaN and GaP binary alloys and there exists a negative deviation from Vegard's law. The Ga-P and Ga-N bond lengths of GaP_1−xN_x alloys reveal a slight relaxation. The incorporation of nitrogen into GaP leads to the giant reduction of the bandgap energy. We have investigated the thermal stabilities and obtained the most stable configurations of the GaP_1−xN_x alloy. In addition, the formation enthalpies have also been calculated, which could explain the difficulty in nitrogen incorporation into GaP.     

Strain engineering for ZnO nanowires: First-principle calculations

We employ density-functional theory to investigate the strain engineering for infinitely long [0001] ZnO nanowires with rectangular cross sections. The structural and electronic properties of ZnO nanowires with uniaxial, lateral and shear strain are systemically calculated. The results show that the band-gaps of ZnONWs will decrease (increase) with increasing (decreasing) tensile (compressive) uniaxial strain. The tensile (compressive) lateral strain on {10 1̅0} surfaces will improve (reduce) the band-gaps for ZnONW with clearly nonlinear characteristic, while the change trend of band-gaps for ZnONW with lateral strain on {1 2̅10} surfaces is basically opposite. When we enhance shear strain on ZnONWs, the band-gaps are reduced. The increasing shear strain along [10 1̅0] direction will sharply reduce the band-gap and the curve is nonlinear, while the band-gap decreases nearly linearly with the increase of shear strain along [1 2̅10] direction.     

Moiré superstructures of silicene on hexagonal boron nitride: A first-principles study

Using first-principles calculations, we predicted hexagonal boron nitride (h-BN) with flat surface is an ideal substrate for silicene. Van der Waals interactions hold silicene and h-BN together, forming silicene/BN moiré superstructures. The moiré superstructures open a band gap of about 30 meV at the Dirac point of silicene at equilibrium distance. The band gap is almost independent of the rotation angle between the two lattices, but can be effectively tuned by changing the interlayer spacing. The high Fermi velocity of silicene is well preserved in these superstructures. These features are helpful in achieving applications of silicene in nanoscale electronic devices.     

Electronic and optical properties of kesterite Cu2ZnSnS4 under in-plane biaxial strains: First-principles calculations

The electronic structures and optical properties of Cu₂ZnSnS₄ (CZTS) under in-plane biaxial strain were systematically investigated using first-principles calculations based on generalized gradient approximation and hybrid functional method, respectively. It is found that the fundamental bandgap at the Γ point decreases linearly with increasing tensile biaxial strain perpendicular to c-axis. However, a bandgap maximum occurs as the compressive biaxial strain is 1.5%. Further increase of compressive strain decreases the bandgap. In addition, the optical properties of CZTS under biaxial strain are also calculated, and the variation trend of optical bandgap with biaxial strain is consistent with the fundamental bandgap.     

甲胺基-甲脒基混合钙钛矿的第一性原理研究

有机铅卤钙钛矿APbX_3的稳定性是制约其应用的重要因素,对APbX_3钙钛矿中A和X采用不同种类离子混合的化学组分调控是改进其稳定性最有效的方式之一。其中,A位点采用不同比例的甲脒离子(FA)和甲胺离子(MA)是当前研究的热点方向。本文通过第一性原理计算,系统研究了FA_(1-x)MA_xPbI_3体系的结构和光电性质。研究发现FA与MA的混合增加体系的稳定性,其中FA_(0.5)MA_(0.5)PbI_3最稳定。通过分析不同混合比例的结构,揭示了晶格常数随x的增加线性减小;以及带隙随x减小而线性增加。此外,计算结果发现MA所占比例增加时吸收光谱蓝移。研究表明通过FA和MA离子的混合能有效调控钙钛矿的光电性质,从而获得更有效的钙钛矿太阳能电池。     

First-principles calculations of stability of graphene-like BC_3 monolayer and its high-performance potassium storage

With increasing demand for renewable energy,graphene-like BC_3 monolayer as high performance electrode materials for lithium and sodium batteries are drawing more attention recently.However,its structural stability,potassium storage properties and strain effect on adsorption properties of alkali metal ions have not been reported yet.In this work,phonon spectra,AIMD simulations and elastic constants of graphene-like BC_3 monolayer are investigated.Our results show that graphene-like BC_3 monolayer possesses excellent structural stability and the maximum theoretical potassium storage capacity can reach up to 1653 mAh/g with the corresponding open circuit voltages 0.66 V.Due to potassium atom can be effectively adsorbed at the most energetically favorable h-CC site with obvious charge transfer,making adsorbed graphene-like BC_3 monolayer change from semiconductor to metal which is really good for electrode utilization.Moreover,the migrations potassium atom on the graphene-like BC_3 monolayer is rather fast with the diffusion barriers as low as 0.12 eV,comparing lithium atom with a relatively large diffusion barrier of 0.46 eV.Additionally,the tensile strains applied on the graphene-like BC_3 monolayer have marginal effect on the adsorption and diffusion performances of lithium,sodium and potassium atoms.     

锂硫电池中钴磷共掺杂MoS2催化性能的第一性原理研究

基于第一性原理计算, 探究了未掺杂、 Co单掺杂、 Co, P共掺杂MoS₂表面上多硫化物的吸附和转化, 揭示了Co, P共掺杂对MoS₂材料吸附能力和催化能力的影响. 研究结果表明, 共掺杂使得MoS₂吸附能力增强, 特别是对产物Li₂S的稳定吸附提供了多硫化物转化动力, 进而增强了催化能力. Co, P共掺杂表面与长链、 中链、 短链多硫化物之间均存在Li—S和S—P双重成键, 具备最大的吸附能力; 另一方面, 共掺杂表面对于产物Li₂S的显著稳定化作用降低了多硫化物转化过程中解离步骤的能量需求, 增大了转化过程的能量释放, 为多硫化物转化提供了驱动力. 上述两方面因素共同增强了MoS₂的催化活性, 有效抑制了穿梭效应, 提升了电池的电化学性能.     

双氮协同钴掺杂锐钛矿相二氧化钛电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理计算了双氮原子协同钴原子共掺杂TiO2的几何结构和电子结构. 计算结果发现: 双氮原子掺杂引起的双空穴位与钴原子形成了较强的耦合作用, 并引起晶格结构发生明显变化. 共掺杂的协同效应引起TiO2禁带宽度变窄,在价带顶和导带底出现大量杂质能级, 从而引起吸收带边发生明显红移. 该掺杂方式对调制TiO2禁带宽度有明显的效果, 有望指导后续的实验合成.