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High-pressure structure and elastic properties of tantalum single crystal:First principles investigation
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Since knowledge of the structure and elastic properties of Ta at high pressures is critical for addressing the recent controversies regarding the high-pressure stable phase and elastic properties, we perform a systematical study on the highpressure structure and elastic properties of the cubic Ta by using the first-principles method. Results show that the initial body-centered cubic phase of Ta remains stable even up to 500 GPa and the high-pressure elastic properties are excellently consistent with the available experimental results. Besides, the high-pressure sound velocities of the single- and polycrystals Ta are also calculated based on the elastic constants, and the predications exhibit good agreement with the existing experimental data. 相似文献
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Structural, electronic, and magnetic properties of boron cluster anions doped with aluminum: BnAl- (2≤n≤9)
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The geometrical structures, relative stabilities, electronic and magnetic properties of small B n Al (2 ≤ n ≤ 9) clusters are systematically investigated by using the first-principles density functional theory. The results show that the Al atom prefers to reside either on the outer-side or above the surface, but not in the centre of the clusters in all of the most stable B n Al (2 ≤ n ≤ 9) isomers and the one excess electron is strong enough to modify the geometries of some specific sizes of the neutral clusters. All the results of the analysis for the fragmentation energies, the second-order difference of energies, and the highest occupied-lowest unoccupied molecular orbital energy gaps show that B 4 Al and B 8 Al clusters each have a higher relative stability. Especially, the B 8 Al cluster has the most enhanced chemical stability. Furthermore, both the local magnetic moments and the total magnetic moments display a pronounced odd-even oscillation with the number of boron atoms, and the magnetic effects arise mainly from the boron atoms except for the B 7 Al and B 9 Al clusters. 相似文献
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Structural,electronic, and magnetic properties of boron cluster anions doped with aluminum:BnAl-(2〈n〈9)
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The geometrical structures, relative stabilities, electronic and magnetic properties of small BnAl-(2〈n〈9)clusters are systematicalyy investigated by using the first-principles density functional theory. The results show that the A1 atom prefers to reside either on the outer-side or above the surface, but not in the centre of the clusters in all of the most stable BnAl-(2〈n〈9) isomers and the one excess electron is strong enough to modify the geometries of some specific sizes of the neutral clusters. All the results of the analysis for the fragmentation energies, the second-order difference of energies, and the highest occupied-lowest unoccupied molecular orbital energy gaps show that B4A1- and B8A1- clusters each have a higher relative stability. Especially, the BsA1-cluster has the most enhanced chemical stability. Furthermore, both the local magnetic moments and the total magnetic moments display a pronounced oddeven oscillation with the number of boron atoms, and the magnetic effects arise mainly from the boron atoms except for the B7A1- and BgA1- clusters. 相似文献
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本文采用基于密度泛函理论的第一性原理平面波赝势和局域密度近似方法,优化了立方和六方氮化硼的几何结构,系统地研究了零温高压下立方和六方氮化硼的几何结构、力学、电学以及光学性质.结构与力学性质研究表明:立方氮化硼的结构更加稳定,两种结构的氮化硼均表现出一定的脆性,而六方氮化硼的热稳定性则相对较差;电学性质研究表明:立方氮化硼和六方氮化硼均为间接带隙半导体,且立方氮化硼比六方氮化硼局域性更强;光学性质结果显示:立方氮化硼和六方氮化硼对入射光的通过性都很好,在高能区立方氮化硼对入射光的表现更加敏感.此外,还研究了高温高压下立方氮化硼的热力学性质,并得到其热膨胀系数、热容、德拜温度和格林艾森系数随温度和压力的变化关系.本文的理论研究阐述了高压下立方氮化硼和六方氮化硼的相关性质,为今后的实验研究提供了比较可靠的理论依据. 相似文献
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本文利用密度泛函理论中的广义梯度近似对碳化钨晶体的三种结构(碳化钨相、闪锌矿相以及纤锌矿相)进行了优化,得到能量最低的稳定构型,并在此基础上计算了它的力学、电子、光学和高温高压下的热力学性质.研究表明:在0~300 GPa压力范围内,碳化钨相具有最高的稳定性.同时,高压下碳化钨相的弹性常数满足Born-Huang准则,且0 GPa和300 GPa下的声子色散没有虚频,证明了高压下碳化钨相的静力学稳定性和动力学稳定性.电子性质表明了碳化钨的金属性.光学性质表明碳化钨在高能区很难吸收光.热力学性质的研究表明:体积比V/V_0对压强的变化更敏感;高温时C_V曲线近似一条直线;给定压强下热膨胀系数α在600 K温度以上增长非常缓慢;压强对德拜温度Θ_D的影响较大;在低压下格林艾森系数γ的变化较大. 相似文献
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