第一性原理研究
(廣西大學(xué) 物理科學(xué)與工程技術(shù)學(xué)院，南寧 530004)
摘 要: 采用基于密度泛函理論(DFT)的平面波贗勢(shì)(PW-PP)方法，計(jì)算并分析了Mg2Ni1−xMx(M=Mn, Fe, Co, Ni, Cu, x=0.25)合金及其氫化物Mg2Ni1−xMxH4的電子結(jié)構(gòu)和熱力學(xué)穩(wěn)定性。計(jì)算結(jié)果表明：Mg2NiH4和Mg2Ni1−xMx的晶胞參數(shù)與實(shí)驗(yàn)值吻合較好。對(duì)Mg2Ni1−xMxH4的電子結(jié)構(gòu)分析發(fā)現(xiàn)：氫化物中的Ni—H和M—H鍵為共價(jià)鍵、Mg—H鍵為離子鍵，且Ni—H與M—H鍵的相互作用強(qiáng)于Mg—H鍵的。Mn、Fe和Co的部分替代對(duì)Ni—H鍵的相互作用影響較小，而Cu的替代則減弱了Ni—H鍵的相互作用，這可能是Cu替代后氫化物結(jié)構(gòu)穩(wěn)定性降低的一個(gè)原因。計(jì)算了Mg2Ni0.75M0.25H4 (M=Mn, Fe, Co, Ni, Cu )的生成焓，分別為−57.7、−61.5、−61.4、63.4和41.6 kJ/mol，與實(shí)驗(yàn)值吻合較好。
關(guān)鍵字: Mg2Ni；第一性原理；電子結(jié)構(gòu)；熱力學(xué)穩(wěn)定性
thermodynamic stability of Mg2Ni hydride:
A first-principle investigation
（College of Physical Science and Technology, Guangxi University, Nanning 530004, China）
Abstract:The electronic structures and thermodynamic stabilities of Mg2Ni1−xMx (M=Mn, Fe, Co, Ni, Cu, x=0.25) alloys and their hydrides Mg2Ni1−xMxH4 were investigated by plane-wave pseudo-potential approach based on the density functional theory. It is found that the calculated cell parameters of Mg2NiH4 and Mg2Ni1−xMx alloy are in good agreement with the experimental results. For Mg2Ni1−xMxH4, the interaction between Mg—H bonds is ionic bond, while the interactions between Ni—H and M—H are covalent bonds, which are stronger than that of Mg—H bonds. The Ni—H bond strength is almost unchanged when Ni is partially replaced by Mn, Fe and Co, and the Ni—H bond strength is weakened when Ni is partially substituted by Cu, which may be one of the reasons for causing the reduced structure stability of Mg2Ni0.75Cu0.25H4. The calculated formation enthalpies of Mg2Ni0.75M0.25H4 (M=Mn, Fe, Co, Ni, Cu) are −57.7, −61.5, −61.4, 63.4 and 41.6 kJ/mol, respectively, which are in good agreement with the experimental results.
Key words: Mg2Ni; first principle; electronic structure; thermodynamic stability
