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1.
蒋文灿  陈华  张伟斌 《物理学报》2016,65(12):126301-126301
利用第一性原理并结合vd W-DF2范德瓦耳斯力校正研究了TATB(C6H6O6N6)晶体声子谱及比热容.采用冷冻声子法计算了TATB晶体声子谱和声子态密度,发现在2.3 THz附近TATB声子态密度最大,证实了太赫兹光谱实验观察到的2.22 THz附近的强吸收峰.基于声子态密度研究了振动模式对比热容的贡献,分析结果表明,常温下0—27.5 THz频段振动模式贡献了比热容的93.7%.同时比较了升温过程中振动模式对比热容的贡献,指出TATB热分解的引发键是C—NO_2键断裂的可能性更大.  相似文献   

2.
采用基于密度泛函平面波赝势方法(PWP)方法,计算了六角晶系2H-PbI2晶体的电子结构、力学性质和硬度.采用局域密度近似(LDA)方法计算的晶格常数、带隙、弹性常数与实验值和理论值符合较好.计算表明,2H-PbI2是一种直接带隙的半导体,带隙大约为2.38eV.运用复杂晶体硬度计算公式计算了六角晶系2H-PbI2晶体的硬度,硬度值大约为2.54GPa.还发现2H-PbI2晶体的各向异性非常明显.  相似文献   

3.
采用Hartree-Fock方法和密度泛函 BPW91方法,对TATB分子的几何结构进行了优化,计算了其电子能量和热运动的能量.计算并讨论了TATB的生成焓.结果表明,TATB分子中的苯环离域电子结构引起TATB生成焓计算的较大的系统偏差;利用具有相似离域电子结构的苯和NO的生成焓进行修正,计算得到的TATB生成热与实验结果符合较好.?  相似文献   

4.
在密度泛函理论的基础上,运用局域密度近似(LDA)和广义梯度近似(GGA)两种方法,并通过第一性原理等方法对锆晶体在0~50 GPa下的物理性质进行了深入、系统的研究.结果表明,相比于广义梯度近似的计算结果而言,局域密度近似的计算结果和实验值更接近,但两者相差不是很大.并通过经典方法对锆晶体模拟计算了高压下的结构性质,得到的结果表明,在讨论的压强范围内,晶格参数与晶胞体积发生了非线性的变化,然而晶胞能量却随压强线性变化.通过对其相应的弹性性质的分析,发现随着压强的增大,锆晶体获得较好的延展性以及力学的稳定性.同时还得到了关于金属锆的能带结构特性及其光学性质,证实压强的改变对金属锆电子性质不会带来太大影响.  相似文献   

5.
采用基于密度泛函平面波赝势方法(PWP)方法,计算了六角晶系2H-PbI2晶体的电子结构、力学性质和硬度。采用局域密度近似(LDA)方法计算的晶格常数、带隙、弹性常数与实验值和理论值符合较好。计算表明,2H-PbI2是一种直接带隙的半导体,带隙大约为2。38eV。运用复杂晶体硬度计算公式计算了六角晶系2H-PbI2晶体的硬度,硬度值大约为2. 54 GPa。还发现2H-PbI2晶体的各向异性非常明显。  相似文献   

6.
TATB分子的结构及分子间相互作用   总被引:2,自引:1,他引:1       下载免费PDF全文
采用Hartree-Fock方法和密度泛函BPW91方法,对TATB双分子系统的几何结构和能量进行了优化和计算,得到双分子共平面的平衡结构.结果表明在TATB分子内部H和O之间存在着明显的氢键.分子之间的相互作用使TATB分子的对称性下降.一般地,没有充分计入分子之间的相互作用的影响时,计算得到的C-N键长比实验测得值大,而计算得到的C-C键长比实验测得值小.计算并讨论了TATB分子之间的相互作用能,表明TATB分子形成晶体结构时,应当以层状晶体结构最为稳定.  相似文献   

7.
采用密度泛函理论B3LYP方法,在6-311g**水平上对TATB的结构进行优化,得到了TATB的稳定几何结构和分子内部质子迁移后形成的亚稳结构,计算了这两个结构的电子能量.对计算结果进行了讨论.  相似文献   

8.
固态氩弹性性质的量子力学从头计算   总被引:1,自引:1,他引:0  
本文从量子力学第一性原理出发,用平面波赝势 (PWP)结合广义梯度近似(GGA)密度泛函理论方法,计算了零温下固态氩晶体0~82 GPa压力范围内的弹性性质,体系电子-离子相互作用采用硬赝势描述.计算结果与静高压实验数据良好相符,通过计算表明采取合理的方法和计算参数,惰性气体固态晶体高压下的力学性质可以比较准确地计算出来,这可为实验上难于进行研究的物质提供有意义的参考.  相似文献   

9.
采用第一性原理密度泛函理论,结合平面波赝势和广义梯度近似(GGA),用虚拟晶体近似(VCA)的方法建立高熵合金的固溶结构模型,计算了高熵合金Al_xFeTiCrZnCu的结构性能、弹性性能和生成热.计算结果表明,Al_xFeTiCrZnCu高熵合金的密度随着Al元素含量的增加而减小,晶格常数在Al元素摩尔含量为1时最小. Al元素含量的增加能提高高熵合金Al_xFeTiCrZnCu的力学稳定性.基态总能量和生成热都随着Al元素含量的增加而增加,但是合金系的稳定性和热力学稳定性有所下降.  相似文献   

10.
采用LSDA(局域自旋密度近似) U(有效库仑相关能)方法计算研究了PuO2的电子结构和成键特征。计算的平衡体积和半导体带隙分别为0.03875 nm3和0.18 eV,与实验结果符合得很好。能态密度和电子密度的分析表明PuO2并不是纯粹的离子晶体,Pu5f和O2p轨道杂化形成共价键。计算结果有助于理解PuO2晶体中Pu5f电子的关联效应。  相似文献   

11.
First-principles calculations based on density functional theory, both with the local density approximation (LDA) and with generalized gradient corrections (GGA), have been used to simulate solid and liquid MgO in direct coexistence in the range of pressure 0 < or = p < or = 135 GPa. The calculated LDA zero pressure melting temperature is T(LDA)m = 3110 +/- 50 K, in good agreement with the experimental data. The GGA zero pressure melting temperature T(GGA)m = 2575 +/- 100 K is significantly lower than the LDA one, but the difference between the GGA and the LDA is greatly reduced at high pressure. The LDA zero pressure melting slope is dT/dp approximately 100 K/GPa, which is more than 3 times higher than the currently available experimental one from Zerr and Boehler [Nature (London) 371, 506 (1994)]. At the core mantle boundary pressure of 135 GPa MgO melts at Tm = 8140 +/- 150 K.  相似文献   

12.
The phase transition of graphite to a diamond-like LA3 phase is simulated by the methods of the density functional theory (DFT). The calculations are performed in the local density approximation (LDA) and the generalized gradient approximation (GGA). It is found that the structural transformation must occur at a pressure of 60 or 74 GPa according to calculations based on the DFT–LDA and DFT–GGA, respectively. The height of the potential barrier separating the structural state corresponding to the LA3 phase from the state corresponding to graphite exceeds 0.13 eV/atom. This indicates the possibility of stable existence of the diamond-like LA3 phase under standard conditions.  相似文献   

13.
The structure, elastic properties and elastic anisotropy of orthorhombic OsB2 are investigated by density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation (GGA) as well as local density approximation (LDA). The obtained structural parameters, elastic constants, elastic anisotropy and Debye temperature for OsB2 under pressure are consistent with the available experimental data and other theoretical results. It is found that the elastic constants, bulk modulus and Debye temperature of OsB2 tend to increase with increasing pressure. It is predicted that OsB2 is not a superhard material from our calculations.  相似文献   

14.
The structural phase stability, elastic parameters and thermodynamic properties of YN at normal and under high pressure are reported. The calculations are mainly performed using the full-potential linearized augmented plane wave method within the density functional theory. Both local density approximation (LDA) and generalized gradient approximation (GGA) are used to model the correlation-exchange potential. The calculated equilibrium lattice parameter and the bulk modulus show good accordance with the experimental and previous theoretical reports. The phase transition from the NaCl (B1) structure to the CsCl (B2) structure is found to occur at 131?GPa within GGA and 115?GPa within LDA. The linear pressure coefficients of the different elastic moduli being addressed here are also determined along with the mechanical and dynamical stability criteria which are shown to be satisfied for YN with B1 phase under normal conditions. Besides, the heat capacity and other thermodynamic parameters are examined and discussed versus temperature.  相似文献   

15.
In the framework of density functional theory, the structural, electronic and lattice dynamical properties of platinum pernitride have been investigated using the plane wave pseudopotential within the GGA and LDA functional for treating the effects of exchange correlation implemented in PWSCF and ABINIT packages. The computed lattice constant and bulk modulus agree well with the experiment and other theoretical calculations. Both packages and correlation functional agree well on the lattice constant within the deviation of about 1.6%. The bulk modulus has been quite successfully predicted by LDA. The electronic structure and DOS of platinum pernitride show a narrow gap and confirms semiconducting nature of this compound. The lattice dynamical calculation shows that the platinum nitride in pyrite structure (platinum pernitride) is dynamically stable. The zone center phonon frequencies particularly the Raman active phonons agree well with the experimental Raman data in the case of GGA implemented in PWSCF. The pressure variation of Raman active modes shows a linear variation; however, at higher pressure the variation is fast.  相似文献   

16.
We report results of first-principles calculations for the electronic and optical properties under pressure effect of Li2O, Na2O, Ki2O and Rb2O compounds in the cubic antifluorite structure, using a full relativistic version of the full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method based on density functional theory, within the local density approximation (LDA) and the generalized gradient approximation (GGA). Moreover, the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is also used for band structure calculations. The calculated equilibrium lattices and bulk moduli are in good agreement with the available data. Band structure, density of states, and pressure coefficients of the fundamental energy gap are given. The critical point structure of the frequency dependent complex dielectric function is also calculated and analyzed to identify the optical transitions. The pressure dependence of the static optical dielectric constant is also investigated.  相似文献   

17.
侯永  袁建民 《物理学报》2007,56(6):3458-3463
在密度泛函理论下,用缀加平面波加局域轨道方法,分别采用广义梯度近似(GGA)和局域密度近似(LDA)对金的面心立方晶格结构(fcc)、体心立方晶格结构(bcc)和六角密堆积结构(hcp)的结构能量进行了计算.在GGA下,计算得出fcc向hcp和hcp向bcc的相变分别发生在380GPa 和1250GPa;而LDA下相变分别发生在490GPa和790GPa.当计算压强达到2TPa时,bcc在这两种近似下仍然保持稳定的结构.根据不同体积下不同结构的电子态密度的特征,对发生相变的物理原因进行了定性的分析,在此基础上得到了金的零温状态方程. 关键词: 缀加平面波方法 固态相变 电子态密度 物态方程  相似文献   

18.
Ab initio total energy calculations have been performed for superconducting GdBa2Cu3O7 and insulating PrBa2Cu3O7 using the full-potential linear augmented plane-wave method in the local density approximation (LDA) and generalized gradient approximation (GGA). The comparison of the calculated unit cell volume and lattice parameters with the experimental data indicates the improvement of these parameters in the GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about 6% smaller and 1.25% larger than the experimental data, respectively for both systems. Thus frozen phonon calculations have been performed to determine the eigenvalues and eigenvectors of the k=0 Ag modes of the two systems in equilibrium structure have been obtained in GGA. The calculated frequencies in the GGA are in good agreement with the other LDA calculations for similar systems. Comparison of computational data with experimental data indicates that calculations determine the frequencies about ten percent below the experimental data. Even by improving LDA to GGA in these calculations, the calculated phonon frequencies have remained almost ten percent below the experimental data, even though the calculated unit cell volumes are nearly equal to the experimental data. So, applying GGA has not considerably decreased the difference between the computational and experimental data. The effect of Pr doping on the eigenvalues and eigenvectors have also been investigated.  相似文献   

19.
Vacancy-induced magnetism in perovskite SrTiO3 is investigated by ab initio calculations and magnetic measurements. The calculations of the generalized gradient approximation (GGA), the local density approximation (LDA) and the local density approximation with on-site effect U (LDA+U) methods show that stoichiometric SrTiO3 is nonmagnetic. The GGA calculated results indicate that Ti or O vacancy could induce magnetism rather than Sr vacancy. The LDA and LDA+U calculations show that the Ti vacancy could induce magnetism, while Sr and O vacancies couldn't. The experimental results confirm that SrTiO3 nanocrystalline powders exhibit room-temperature ferromagnetism (FM) and the magnetic moment results from cation vacancies.  相似文献   

20.
The electric field effect in ultrathin zigzag graphene nanoribbons containing only three or four zigzag carbon chains is studied by first-principles calculations, and the change of conducting mechanism is observed with increasing in-plane electric field perpendicular to the ribbon. Wider zigzag graphene nanoribbons have been predicted to be spin-splitted for both valence band maximum(VBM) and conduction band minimum(CBM) with an applied electric field and become half-metal due to the vanishing band gap of one spin with increasing applied field. The change of VBM for the ultrathin zigzag graphene nanoribbons is similar to that for the wider ones when an electric field is applied. However, in the ultrathin zigzag graphene nanoribbons, there are two kinds of CBMs, one is spin-degenerate and the other is spin-splitted, and both are tunable by the electric field. Moreover, the two CBMs are spatially separated in momentum space. The conducting mechanism changes from spin-degenerate CBM to spin-splitted CBM with increasing applied electric field. Our results are confirmed by density functional calculations with both LDA and GGA functionals, in which the LDA always underestimates the band gap while the GGA normally produces a bigger band gap than the LDA.  相似文献   

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