Dipole‐Field Sums, Lorentz Factors, and Dielectric Properties of Organic Molecular Films Modeled as Crystalline Arrays of Polarizable Points
Dipole‐Field Sums, Lorentz Factors, and Dielectric Properties of Organic Molecular Films Modeled as Crystalline Arrays of Polarizable Points
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作为可极化点晶体阵列建模的有机分子薄膜的偶极场和、洛伦兹因子和介电性能
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发表时间：
2015
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通讯作者：
Z. Soos
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作者：
D. Vanzo;B. J. Topham;Z. Soos
有机电子器件中所用薄膜的相对介电常数κ = ε/ε0与薄膜的结构和分子间重叠较小时的分子极化率α直接相关。单层和多层膜被建模为具有感应偶极子μ = αF的可极化点的晶格，其中内部电场F包括来自所有感应偶极子的贡献。对于数密度n，单位体积的极化率为P = nμ。通过无限层的堆叠，直接计算原子和分子晶体和薄膜的偶极场和。小于立方对称的均匀极化晶体中的洛伦兹因子完全解决了三维偶极场和的条件收敛。薄膜在层内具有相等的P，但在表面或表面附近则不然。表面效应随αn的增加而增加，有时甚至延伸到薄膜中，即使偶极场主要是由于相邻层。简单的和体心的四面体晶格示出了层之间的极化或去极化相互作用，所述层模拟在膜或SAM中从法线到表面以角度Φ倾斜的分子或低聚物。分子膜中的均匀P指的是晶胞而不是原子，并且有多种方法将各向异性分子α在可极化点之间分配。一个说明性的分析模型的基础上的极化点和偶极场的相邻层被施加到oligophenyl膜和共轭分子并苯膜。
The relative permittivity κ = ε/ε0 of thin films used in organic electronic devices is directly related to the structure and the molecular polarizability α when intermolecular overlap is small. Monolayer and multilayer films are modeled as lattices of polarizable points with induced dipoles μ = αF where the internal electric field F includes contributions from all induced dipoles. The polarization per unit volume is P = nμ for number density n. Dipole‐field sums are evaluated directly for atomic and molecular crystals and films through stacking of infinite layers. Lorentz factors in uniformly polarized crystals of less than cubic symmetry resolve completely the conditional convergence of dipole‐field sums in three dimensions. Thin films have equal P within layers but not at or near the surface. Surface effects are shown to increase with αn and sometimes to extend into films even though dipole fields are mainly due to adjacent layers. Simple and body‐centered tetragonal lattices illustrate polarizing or depolarizing interactions between layers that mimic molecules or oligomers tilted at angle Φ from normal to the surface in films or SAMs. Uniform P in molecular films refers to unit cells rather than to atoms and there are multiple ways to partition anisotropic molecular α among polarizable points. An illustrative analytical model based on polarizable points and dipole fields of adjacent layers is applied to oligophenyl films and to conjugated molecules in acene films.