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以在可见光区有吸收峰的Cs构型的Si2N2分子团簇为研究对象，利用密度泛函B3LYP方法，在aug-cc-pVTZ基组水平下优化得到了处于不同外电场中的Si2N2分子团簇的稳定结构. 分析发现：在不同的外电场中，Si2N2分子构型对称性没有发生改变，均为Cs对称性，且都有6种振动模式；随着外电场强度的逐渐增大，Si2N2 分子振动频率较低的前三种振动模式的频率略有减小，而后三种振动模式的频率逐渐增加；随着外电场强度的逐渐增大，在一定电场范围内最高占据分子轨道与最低空分子轨道的能隙值出现振荡，之后能隙值随着外电场强度的增大而减小. 在此基础上，采用含时密度泛函TD-B3LYP方法研究了外电场对Si2N2分子吸收谱的影响规律. 计算得到的吸收谱范围在紫外-可见光区，这与实验值相符合. 随着外电场强度的逐渐增大，在可见光区吸收谱发生红移，最大跃迁振子强度逐渐增大. 结果表明，施加外电场有利于Si2N2分子在可见光区的吸收，也有利于操控分子特定激发态的电子状态，进而调节相应的跃迁光谱特性，可达到获得所需特定波长的要求.In order to understand in depth the electroluminescence mechanism, the influences of the external electric field on the geometric and electronic structure in ground state, the molecular vibrational spectra of Si2N2 molecule with Cs special symmetry are studied by density functional theory with B3LYP exchange-correlation prescription at the aug-cc-pVTZ basis set level. Following each optimization, the vibrational frequencies are calculated and all optimized structures are stable. The results show that the molecular vibrational Stark effect, i.e., red-shift for the low-frequency modes and blue-shift for the high-frequency modes are observed with the increase of the applied field strength. The energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), the energy gap between HOMO and LUMO of Si2N2 molecule diminish with the increase of external field. A time-dependent density functional theory is used to investigate the excited properties of Si2N2 (Cs) molecule. The calculated absorption spectra of Si2N2 molecule with Cs symmetry are in agreement with the experiment values. The analysis reveals that the absorption spectrum wavelength increases in the visible region with a concomitant increase in the electronic transition oscillator strengths in the course of the increase of the external electric field strength. The results reveal that the excited properties of Si2N2 molecule can be easily tuned by the external electric field, which indicates that the silicon nitride is an interesting optoelectronic functional material. These investigations on the various properties of Si2N2 molecule with Cs symmetry under an external electric field are useful to understand the electroluminescence mechanism for silicon nitride used in molecular electronics.
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Keywords:
- Si2N2 /
- external electric field /
- excitation properties
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[1] Alonso J C, Pulgarín F A, Monroy B M, Benami A, Bizarro M, Ortiz A 2010 Thin Solid Films 518 3891
[2] Pei Z, Chang Y R, Hwang H L 2002 Appl. Phys. Lett. 80 2839
[3] Xu Y N, Ching W Y 1995 Phys. Rev. B 51 17379
[4] Dong L J, Liu Y Z, Chen D P, Wang X B 2005 Chin. J. Lumin. 26 380 (in Chinese) [董立军, 刘渝珍, 陈大鹏, 王小波 2005 发光学报 26 380]
[5] Li D S, Huang J H, Yang D R 2009 Physica E 41 920
[6] Li D S, Wang F, Yang D R 2013 Nanoscale 5 3435
[7] Huang R, Dong H P, Wang D Q, Chen K J, Ding H L, Xu J, Li W, Ma Z Y 2009 Acta Phys. Sin. 58 2072 (in Chinese) [黄锐, 董恒平, 王旦清, 陈坤基, 丁宏林, 徐骏, 李伟, 马忠元 2009 58 2072]
[8] Lin J, Yang P Z, Hua Q L 2013 Acta Opt. Sin. 33 0231003 (in Chinese) [林娟, 杨培志, 化麒麟 2013 光学学报 33 0231003]
[9] Wang Y, Shen D Z, Zhang J Y, Liu Y C, Zhang Z Z, L Y M, Fan X W 2005 Chin. J. Liq. Cryst. Displays 20 18 (in Chinese) [王颖, 申德振, 张吉英, 刘益春, 张振中, 吕有明, 范希武 2005 液晶与显示 20 18]
[10] Xie Z F, Shan W G, Wu X S, Zhang F M 2012 Chin. J. Lumin. 33 780 (in Chinese)[谢正芳, 单文光, 吴小山, 张凤鸣 2012 发光学报 33 780]
[11] Zeng Y H, Guo H Q, Wang Q M 2007 Semicond. Optoelectron. 28 209 (in Chinese)[曾友华, 郭亨群, 王启明 2007 半导体光电 28 209]
[12] Matsuoka M, Isotani S, Sucasaire W, Zambom L S, Ogata K 2010 Surf. Coat. Technol. 204 2923
[13] Liao W G, Zeng X B, Wen G Z, Cao C C, Ma K P, Zheng Y J 2013 Acta Phys. Sin. 62 126801 (in Chinese) [廖武刚, 曾祥斌, 文国知, 曹陈晨, 马昆鹏, 郑雅娟 2013 62 126801]
[14] Li E L, Ma H, Ma D M, Wang X W, Liu M C, Yuan Y X, Wang X 2008 Acta Photon. Sin. 37 2024 (in Chinese) [李恩玲, 马红, 马德明, 王雪文, 刘满仓, 苑永霞, 王雪 2008 光子学报 37 2024]
[15] Xu G L, Xie H X, Yuan W, Zhang X Z, Liu Y F 2012 Chin. Phys. B 21 53101
[16] Ye J Z, Li B X 2010 Physica B 405 1461
[17] Ornellas F R, Iwata S 1996 J. Phys. Chem. 100 10919
[18] Jackson K, Jungnickel G, Frauenheim T 1998 Chem. Phys. Lett. 292 235
[19] Goldberg N, Iraqi M, Schwarz H, Boldyrev A, Simons J 1994 J. Chem. Phys. 101 2871
[20] Ornellas F R, Iwata S 1996 J. Phys. Chem. 100 16155
[21] Jungnickel G, Frauenheim T, Jackson K A 2000 J. Chem. Phys. 112 1295
[22] Wu D L, Tan B, Wan H J, Zhang X Q, Xie A D 2013 Chin. Phys. B 22 123101
[23] Ling Z G, Tang Y L, Li T, Li Y P, Wei X N 2013 Acta Phys. Sin. 62 223102 (in Chinese) [凌智钢, 唐延林, 李涛, 李玉鹏, 魏晓楠 2013 62 223102]
[24] Becke A D 1993 J. Chem. Phys. 98 5648
[25] Lee C, Yang W, Parr R G 1988 Phys. Rev. B 37 785
[26] Burke K, Werschnik J, Gross E K U 2005 J. Chem. Phys. 123 62206
[27] Chiba M, Tsuneda T, Hirao K 2006 J. Chem. Phys. 124 144106
[28] Han L Z, Wang Z, Hua Y J, Ren A M, Liu Y L, Liu P J 2012 Acta Chim. Sin. 70 579 (in Chinese) [韩立志, 王卓, 华英杰, 任爱民, 刘艳玲, 刘朋军 2012 化学学报 70 579]
[29] Lin J, Yang P Z, Hua Q L 2012 Chin. J. Lumin. 33 596 (in Chinese) [林娟, 杨培志, 化麒麟 2012 发光学报 33 596]
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