詹國(guó)富， 莫玉梅

(廣東理工學(xué)院 工業(yè)自動(dòng)化系，廣東 肇慶 526100)

二氮化鋨結(jié)構(gòu)和彈性性質(zhì)的第一性原理計(jì)算

詹國(guó)富， 莫玉梅

(廣東理工學(xué)院 工業(yè)自動(dòng)化系，廣東 肇慶 526100)

研究了在瑩石結(jié)構(gòu)(C1)，黃鐵礦結(jié)構(gòu)(C2)和白鐵結(jié)構(gòu)(C18)下二氮化鋨的結(jié)構(gòu)和彈性性質(zhì)。通過(guò)密度泛函理論，計(jì)算了它不同的結(jié)構(gòu)參數(shù)和體彈模量、剪切模量以及彈性常數(shù)。彈性常數(shù)的計(jì)算反應(yīng)了OsN2具有很強(qiáng)的硬度。

密度泛函理論；結(jié)構(gòu)參數(shù)；彈性性質(zhì)

過(guò)渡金屬的氮化物、氧化物、硼化物等因其優(yōu)越的物理化學(xué)性質(zhì)，諸如耐高溫、半導(dǎo)體性質(zhì)、超導(dǎo)性能等[1]，因而在光學(xué)涂層、耐磨涂層、切割工具方面有著廣泛地應(yīng)用[2]。眾多研究3d和4d金屬化合物的工作已經(jīng)做過(guò)了，而鉑、銥、銠的氮化物在極端條件下相繼被合成出來(lái)[3-7]，相關(guān)的性質(zhì)也有了一定的研究。作為過(guò)渡金屬的二氮化鋨，它的一些常溫常壓下的結(jié)構(gòu)性質(zhì)、電子結(jié)構(gòu)等都有了一定的了解[8,9]。

1 理論計(jì)算方法

總能量計(jì)算是基于密度泛函理論，采用Perdew-Burke-Ernergof(PBE)交換關(guān)聯(lián)泛函[10]和廣義梯度近似(GGA)的交換關(guān)聯(lián)勢(shì)。整個(gè)計(jì)算過(guò)程用Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA)[11]計(jì)算完成。采用原子軌道線性組合方法來(lái)計(jì)算總能和原子間作用力。采用Sanky-niklewsky贗原子軌道[12](PAOs)形成贗勢(shì)，電子與芯核之間的相互作用通過(guò)分離的Troullier-Martins[13]模守恒贗勢(shì)來(lái)模擬。對(duì)于鋨來(lái)說(shuō)，其價(jià)電子為5d66s2，而對(duì)于氮來(lái)說(shuō)價(jià)電子為2s22p3。為了達(dá)到一定要求的計(jì)算精度，所以原子弛豫到原子間作用力小于0.04eV/?；瑩石結(jié)構(gòu)(C1)、黃鐵礦結(jié)構(gòu)(C2)、白鐵礦結(jié)構(gòu)(C18)的截?cái)嗄芊謩e為700eV、800eV和700eV；布里淵區(qū)積分采用Monkhorst-Pack形式的K點(diǎn)網(wǎng)格，分別取12×12×12、12×12×12、15×12×11，所有自洽計(jì)算最后能量的收斂精度都達(dá)到0.1meV/atom。

2 結(jié)果與討論

通過(guò)對(duì)OsN2三種結(jié)構(gòu)進(jìn)行結(jié)構(gòu)(C1瑩石結(jié)構(gòu)、C2黃鐵礦結(jié)構(gòu)、C18白鐵礦結(jié)構(gòu))優(yōu)化，在優(yōu)化過(guò)種中允許對(duì)原胞參數(shù)和坐標(biāo)進(jìn)行弛豫，得到不同結(jié)構(gòu)的能量—體積曲線后。通過(guò)Brich-Murnaghan狀態(tài)方程[11,12]對(duì)能量-體積曲線進(jìn)行擬合，得到零溫零壓三種結(jié)構(gòu)的晶格參數(shù)、體積和體模量及其一階導(dǎo)數(shù)和其它的理論實(shí)驗(yàn)結(jié)果，一起列在了表1中。從中可以看到，計(jì)算結(jié)果總體上來(lái)說(shuō)與其它的計(jì)算結(jié)果、實(shí)驗(yàn)結(jié)果比較一致。

其次，計(jì)算了三個(gè)結(jié)構(gòu)的彈性常數(shù)(C1瑩石結(jié)構(gòu)、C2黃鐵礦結(jié)構(gòu)、C18白鐵礦結(jié)構(gòu))，體彈模量，剪變模量以及楊氏模量，同時(shí)列出了其它的計(jì)算結(jié)果與相關(guān)的實(shí)驗(yàn)結(jié)果。從表2中可以看到，計(jì)算結(jié)論與相關(guān)理論計(jì)算結(jié)果及實(shí)驗(yàn)結(jié)果吻合的比較好。

表1 零溫零壓下二氮化鋨的晶格參數(shù)(?)，平衡態(tài)體積(?3)，體彈模量(GPa)以及體彈模量一階導(dǎo)數(shù)

aRef.[14],bRef.[10],cRef.[15]dRef.[16]eRef.[6]

表2 零溫零壓下二氮化鋨的彈性常數(shù)、體模量、切變模量及楊氏模量計(jì)算結(jié)果

aRef.[14],bRef.[10],cRef.[9]

3 總結(jié)

從晶體結(jié)構(gòu)參數(shù)及相應(yīng)的體彈模量的討論可以發(fā)現(xiàn)，OsN2具有較高硬度，能夠承受的壓力非常大。不同結(jié)構(gòu)的彈性常數(shù)顯示其彈性性質(zhì)各向異性。C1結(jié)構(gòu)和C2結(jié)構(gòu)各彈性常數(shù)比較接近，反映出其結(jié)構(gòu)較相似；而C18結(jié)構(gòu)的各彈性常數(shù)與C1、C2結(jié)構(gòu)相差較大，反映其結(jié)構(gòu)上的差異很大。

[1] WU Z, ZHAO E. Structural stability and electronic properties of Co2N, Rh2N and Ir2N[J]. Journal of Physics and Chemistry of Solids, 2008, 69(11): 2723-2727.

[2] TOTH L E. Transition metal carbides and nitrides [M]. New York: Academic press, 1974.

[3] GREGORYANZ E, SANLOUP C, SOMAYAZULU M, et al. Synthesis and characterization of a binary noble metal nitride[J]. Nature materials, 2004, 3(5): 294-297.

[4] CROWHURST J C, GONCHAROV A F, SADIGH B, et al. Synthesis and characterization of the nitrides of platinum and iridium[J]. Science, 2006, 311: 1275-1278.

[5] JUN L, XIAO Y K, ZHEN H W, et al. Pressure-induced structural transition and thermodynamic properties of RhN2and the effect of metallic bonding on its hardness[J]. Chinese Physics B, 2012, 21(8): 086103-086107.

[6] YOUNG A F, SANLOUP C, GREGORYANZ E, et al. Synthesis of novel transition metal nitrides IrN2and OsN2[J]. Physical review letters, 2006, 96(15): 155501-155505.

[7] CROWHURST J C, GONCHAROV A F, SADIGH B, et al. Synthesis and characterization of nitrides of iridium and palladium[J]. Journal of Materials Research, 2008, 23(1): 1-5.

[8] FAN C Z, ZENG S Y, LI L X, et al. Potential superhard osmium dinitride with fluorite and pyrite structure: First-principles calculations[J]. Phys. Rev. B. 2006, 74 (12):125118-125123.

[9] WU Z, HAO X, LIU X, et al. Structures and elastic properties of OsN2investigated via first-principles density functional calculations[J]. Physical Review B, 2007, 75(5): 054115-054119.

[10] PERDEW J P, BURKE K, ERNZERHOF M. Generalized gradient approximation made simple[J]. Physical review letters, 1996, 77(18): 3865-3869.

[11] ORCLEJON P, ARTACHO E，SOLER J M. Self-consistent order-N density-functional calculations for very large systems[J]. Phys. Rev. B (Rapid Commun). 1996, 53(16): 10441-10446.

[12] SOLER J M, ARTACHO E, GALE J D, et al. The SIESTA method for ab initio order-N materials simulation[J]. Journal of Physics: Condensed Matter, 2002, 14(11): 2745-2749.

[13] SANKEY O F, NIKLEWSKI D J. A initio multicenter tight-binding model for molecular-dynamics simulations and other applications in covalent systems[J]. Physical Review B, 1989, 40(6): 3979-3984.

[14] ZHANG M, WANG M, CUI T, et al. Electronic structure, phase stability, and hardness of the osmium borides, carbides, nitrides, and oxides: First-principles calculations[J]. Journal of Physics and Chemistry of Solids, 2008, 69(8): 2096-2102.

[15] LIU C M, GE N N, FU Z J, et al. PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES: Structural and thermodynamic properties of OsN2from first-principles calculations[J]. Chinese Physics B, 2011, 20(4): 045101-045104.

[16] WU Z, HAO X, LIU X, et al. Structures and elastic properties of OsN2investigated via first-principles density functional calculations[J]. Physical Review B, 2007, 75(5): 054115- 054120.

Structure and Elastic Properties of OsN2from First-principles Study

ZHAN Guo-fu, MO Yu-mei

(Department of Industrial Automation, Guang Dong Polytechnic College, Zhaoqing Guangdong 526100, China)

We have studied the structure and elastic properties of OsN2in fluorite, pyrite and marcasite. The equilibrium lattice parameter, bulk modulus ,its pressure derivative and elastic modulus are calculated. The result of elastic modulus indicate the hardness of OsN2is high.

density functional theory; structure parameter; elastic properties

2016-09-29

沖壓模具設(shè)計(jì)精品資源共享課(JPKC2015003)

詹國(guó)富(1988-)，男，江西鄱陽(yáng)人，碩士，主要從事原子分子結(jié)構(gòu)與光譜結(jié)構(gòu)分析，超硬材料的彈性和熱力學(xué)性質(zhì)計(jì)算。E-mail: qingkongyiye@163.com

O469

A

1004-2237(2016)06-0060-03

10.3969/j.issn.1004-2237.2016.06.013