The role of polymorphism in organic thin films: oligoacenes investigated from first principles
The role of polymorphism in organic thin films: oligoacenes investigated from first principles
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DOI：
10.1088/1367-2630/11/12/125010
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发表时间：
2009-12-11
影响因子：
3.3
通讯作者：
Meisenbichler, Christian
中科院分区：
文献类型：
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作者：
Ambrosch-Draxl, Claudia;Nabok, Dmitrii;Meisenbichler, Christian
我们在密度泛函理论的框架内研究了低聚并苯的内聚性质，包括货车德瓦尔斯相互作用。相比之下，我们评估的局部密度近似以及梯度校正，但也是一个广泛使用的半经验程序占远程色散力，在他们的表现为这样的弱约束系统的能量。除了内聚能，我们详细讨论的表面能，反过来，允许获得的晶体形状的基础上武尔夫的建设低聚物系列从萘并五苯。特别是，我们专注于比较两种不同的并五苯多晶型物，即所谓的块状结构和薄膜相，后者主要存在于薄膜生长中。我们不仅研究这些多面体的细节上的分子构象的影响，而且考虑的指数平面的数量和潜在的交换相关功能的作用的影响。基于弛豫晶体结构的两个多晶型相，我们计算的电子能带结构以及光谱。为了解释激子效应，在后者中，我们解决的Bethe-Salpeter方程的电子空穴对，从而考虑共振和反共振项之间的耦合。
We investigate the cohesive properties of oligoacenes within the framework of density functional theory including van der Waals interactions. In comparison, we evaluate the local density approximation as well as gradient corrections, but also a widely used semiempirical procedure accounting for the long-range dispersive forces, in terms of their performance for the energetics of such weakly bound systems. Besides the cohesive energies we discuss in detail the surface energies which, in turn, allow for obtaining the crystal shapes based on Wulff's construction for the oligomer series from naphthalene to pentacene. In particular, we focus on comparing two different pentacene polymorphs, i.e. the so-called bulk structure and the thin film phase, the latter being predominately found in thin film growth. We not only study the impact of molecular conformation on the details of these polyhedra, but also the influence of the number of considered index planes and the role of the underlying exchange correlation functional. Based on the relaxed crystal structures for the two polymorphic phases, we compute the electronic band structures as well as the optical spectra. To account for excitonic effects in the latter, we solve the Bethe-Salpeter equation for the electron-hole pairs, thereby considering the coupling between resonant and anti-resonant terms.