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Terahertz (THz) technology developed rapidly in recent years. Liquid crystals (LCs) are one of the most promising base materials to construct switchable devices in THz range because of their high optical anisotropies. However, the practical applications of the devices are hampered by the relationships between birefringence, thickness and LCs switching time. Due to the long wavelength, THz device requires a larger birefringence LC than the device operated at optical frequencies. Yet, in order to design an efficient switchable LC-THz device, it is crucial to find or synthetize LC material which will still display a useful birefringence at THz frequencies. The birefringence properties of LC are determined by the molecular polarizability of the relevant material. Knowledge of the LC molecular polarizability and its dependence on the molecular structure is important for designing LC molecules with desired THz properties. The prediction of the photoelectric characteristics could save a considerable quantity of the man-power and materials needed for the design or synthesis of new LC compounds. A priori screening of materials and the prediction of the optoelectronic properties would make a vast opportunity for expanding the LC material application scope. Hence, the main purpose of the present work is to provide a theoretical method of calculating and analyzing the THz polarizability properties of LC single compounds for LC-THz device applications. In this work, the frequency dependent molecule polarizability values of liquid crystal PCH5, 5CB and 5OCB in THz range are calculated by the density functional theory method. The geometries of the studied LCs are optimized at B3 LYP levels with the standard 6-311G(d) basis set. From the optimized geometries the molecule THz polarizabilities of LCs are calculated by the M06-2x functional with 6-311++G(2d, p) basis set, and they are found to be in good agreement with experimental data. By plotting the polarizability density analysis (PDA), the spatial contributions of electrons to the longitudinal polarizability are presented. The influences of alkyl chain and core structure on the microscopic polarizability of the LC molecule are investigated and explained by using the finite field approach and PDA. The results show that the unsaturated group, such as benzene ring or cyanobenzyl, makes great contribution to the polarizability of LC. In the design process, the new type of LC molecule must be extended the length of up electron conjugated system, to reduce the energy gap between HOMO and LUMO, and hence improving LC molecule polarizabilty. We hope that the present work could give a useful guide in screening or designing LC molecules for THz applications, and offer an effective way to understand fundamental optoelectronic characteristic of LC materials in the THz frequency range.
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Keywords:
- terahertz /
- liquid crysta /
- polarizability /
- density functional theory
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[4] Lee M, Wanke M C 2007 Science 316 64
[5] Zhao W, Ju D, Jiang Y 2014 Appl. Phys. Express 7 124301
[6] Nakanishi H, Fujiwara S, Takayama K, Kawayama I, Murakami HTonouchi M 2012 Appl. Phys. Express 5 112301
[7] O'hara J F, Withayachumnankul W, Al-Naib I 2012 J. Infrared Millim. Te. 33 245
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[9] Chodorow U, Parka J, Garbat K, Pałka N, Czupryński K 2012 Phase Transitions 85 337
[10] Chen Z Z, Zhao H Z, Li M, Bu J, Ma H 2015 Electro. Compon. Mater. 34 1 (in Chinese) [陈泽章, 赵红枝, 李萌, 补婧, 马恒 2015 电子元件与材料 34 1]
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[13] Chen H T, Padilla W J, Cich M J, Azad A K, Averitt R D, Taylor A J 2009 Nat. Photonics 3 148
[14] Zhu G, Li J N, Lin X W, Wang H F, Hu W, Zheng Z G, Cui H Q, Shen D, Lu Y Q 2012 J. Soc. Inf. Display 20 341
[15] Savo S, Shrekenhamer D P, Adilla W J 2014 Adv. Opt. Mater. 2 275
[16] Shrekenhamer D, Chen W C P, Adilla W J 2013 Phys. Rev. Lett. 110 177403
[17] Yang F Z 2015 Acta Phys. Sin. 64 124214 (in Chinese) [杨傅子 2015 64 124214]
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[19] Vieweg N, Shakfa M, Koch M 2011 J. Infrared Millim. Te. 32 1367
[20] Chen Z, Jiang Y, Jiang L, Ma H 2016 Spectrochim. Acta A 153 741
[21] Park H, Parrott E P, Fan F, Lim M, Han H, Chigrinov V G, Pickwell M E 2012 Opt. Express 20 11899
[22] Reuter M, Garbat K, Vieweg N, Fischer B M, Dąbrowski R, Koch M, Dziaduszek J, Urban S 2013 J. Mater. Chem. C 1 4457
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[25] Li J, Wu S T 2004 J. Appl. Phys. 96 6253
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[28] Frisch M, Trucks G, Schlegel H B, Scuseria G, Robb M, Cheeseman J, Scalmani G, Barone V, Mennucci B, Petersson G 2009 Inc. Wallingford, CT 200 2
[29] Zhao Y, Truhlar D G 2011 Chem. Phys. Lett. 502 1
[30] Zhao Y, Truhlar D G 2008 J. Chem. Theor. Comput. 4 1849
[31] Simpson S, Richardson R, Hanna S 2005 J. Chem. Phys. 123 134904
[32] Lu T, Chen F 2012 J. Comput. Chem. 33 580
[33] Humphrey W, Dalke A, Schulten K 1996 J. Mol. Graphics. 14 33
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[1] Xu J Z, Zhang X C 2007 Terahertz Science and Technology and Application (Beijing: Bejing University Press) p1 (in Chinese) [许景周, 张希成2007 太赫兹科学技术和应用 (北京: 北京大学出版社) 第1页]
[2] Lee Y Z (translated by Cui W Z) 2012 Principles of Terahertz Science and Technology (Beijing: National Defend Industy Press) pp1-3 (in Chinese) [李允植 著 (崔万照 译) 2012 太赫兹科学与技术原理 (北京: 国防工业出版社)第1-3页]
[3] Chen Z Z, Jiang Y R, Li M, Jiang L L, Ma H 2015 Liq. Cryst. 42 947
[4] Lee M, Wanke M C 2007 Science 316 64
[5] Zhao W, Ju D, Jiang Y 2014 Appl. Phys. Express 7 124301
[6] Nakanishi H, Fujiwara S, Takayama K, Kawayama I, Murakami HTonouchi M 2012 Appl. Phys. Express 5 112301
[7] O'hara J F, Withayachumnankul W, Al-Naib I 2012 J. Infrared Millim. Te. 33 245
[8] Shi S C, Li J, Zhang W, Miao W 2015 Acta Phys. Sin. 64 228501 (in Chinese) [史生才, 李婧, 张文, 缪巍 2015 64 228501]
[9] Chodorow U, Parka J, Garbat K, Pałka N, Czupryński K 2012 Phase Transitions 85 337
[10] Chen Z Z, Zhao H Z, Li M, Bu J, Ma H 2015 Electro. Compon. Mater. 34 1 (in Chinese) [陈泽章, 赵红枝, 李萌, 补婧, 马恒 2015 电子元件与材料 34 1]
[11] Feng W, Zhang R, Cao J C 2015 Acta Phys. Sin. 64 229501 (in Chinese) [冯伟, 张戎, 曹俊诚 2015 64 229501]
[12] Chen C Y, Hsieh C F, Lin Y F, Pan R P, Pan C L 2004 Opt. Express 12 2625
[13] Chen H T, Padilla W J, Cich M J, Azad A K, Averitt R D, Taylor A J 2009 Nat. Photonics 3 148
[14] Zhu G, Li J N, Lin X W, Wang H F, Hu W, Zheng Z G, Cui H Q, Shen D, Lu Y Q 2012 J. Soc. Inf. Display 20 341
[15] Savo S, Shrekenhamer D P, Adilla W J 2014 Adv. Opt. Mater. 2 275
[16] Shrekenhamer D, Chen W C P, Adilla W J 2013 Phys. Rev. Lett. 110 177403
[17] Yang F Z 2015 Acta Phys. Sin. 64 124214 (in Chinese) [杨傅子 2015 64 124214]
[18] Vieweg N, Shakfa M K, Scherger B, Mikulics M, Koch M 2010 J. Infrared Millim. Te. 31 1312
[19] Vieweg N, Shakfa M, Koch M 2011 J. Infrared Millim. Te. 32 1367
[20] Chen Z, Jiang Y, Jiang L, Ma H 2016 Spectrochim. Acta A 153 741
[21] Park H, Parrott E P, Fan F, Lim M, Han H, Chigrinov V G, Pickwell M E 2012 Opt. Express 20 11899
[22] Reuter M, Garbat K, Vieweg N, Fischer B M, Dąbrowski R, Koch M, Dziaduszek J, Urban S 2013 J. Mater. Chem. C 1 4457
[23] Li J, Gauza S, Wu S T 2004 J. Appl. Phys. 96 19
[24] Li J, Wu S T 2004 J. Appl. Phys. 95 896
[25] Li J, Wu S T 2004 J. Appl. Phys. 96 6253
[26] Hui Y W, Ajay C, Shyi L L 2005 J. Comput. Chem. 26 1543
[27] Chang C K, Deshmukh V, Chaudhari A, Lee S L 2013 J. Comput. Theor. Nanosic. 10 684
[28] Frisch M, Trucks G, Schlegel H B, Scuseria G, Robb M, Cheeseman J, Scalmani G, Barone V, Mennucci B, Petersson G 2009 Inc. Wallingford, CT 200 2
[29] Zhao Y, Truhlar D G 2011 Chem. Phys. Lett. 502 1
[30] Zhao Y, Truhlar D G 2008 J. Chem. Theor. Comput. 4 1849
[31] Simpson S, Richardson R, Hanna S 2005 J. Chem. Phys. 123 134904
[32] Lu T, Chen F 2012 J. Comput. Chem. 33 580
[33] Humphrey W, Dalke A, Schulten K 1996 J. Mol. Graphics. 14 33
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