Polar Shift: Charge carrier polarization energies in organic electronic materials

Electronic polarization of charge carriers in the solid state plays an important role in organic electronics, as it alters the gas phase energy levels associated with phenomena such as charge transport, molecular doping, charge injection and charge separation at interfaces. In this article we present Polar Shift, a software package for calculating the polarization energy of an electron or hole charge carrier in organic electronic materials. The software uses an atomistic approach employing the microelectrostatics model. Molecular charge distributions are represented by atomic point charges, while the molecular polarizability is divided into distributed atomic contributions. The electrostatic and inductive components of the polarization energy are calculated separately. For the electrostatic interactions we propose an efficient cutoff–based scheme that allows fast yet accurate evaluation of the relevant energy. For the induction part we use a self–consistent iterative method based on modified field interaction tensors in the framework of the Thole model. Polar Shift can be applied to ideal molecular crystals, thermally disordered crystalline packings or completely amorphous materials. Many additional features are implemented such as calculation of the molecular polarizability tensor, fitting of molecular polarizabilities to reference values, different schemes for computing induction energies, and extrapolation of induction energies to the bulk limit. Special attention has been paid to the interoperability with other software packages, so Polar Shift can obtain the required input from various widely used file types such as pdb, mol2 or even binary dcd files. The software is parallelized using the MPI standard thus exploiting a wide range of shared and distributed memory computer architectures. Polar Shift is applied to eight different test cases of prototype organic electronics materials demonstrating its capabilities, and the results are compared with existing literature.固态载流子的电子极化在有机电子学领域具有重要意义，其会改变与电荷输运、分子掺杂、界面电荷注入及电荷分离等现象相关的气相能级。本文介绍了一款用于计算有机电子材料中电子或空穴载流子极化能的软件包Polar Shift。该软件采用基于微静电学模型的原子级模拟方法：分子电荷分布以原子点电荷形式表征，而分子极化率则被拆解为分布式原子贡献项。极化能的静电相互作用分量与感应分量可分别计算。针对静电相互作用，本文提出了一种基于截断的高效方案，能够在保证精度的前提下快速计算相关能量；对于感应分量，则采用基于Thole模型（Thole model）框架下修正场相互作用张量的自洽迭代方法。Polar Shift可应用于理想分子晶体、热无序晶体堆积结构乃至完全无定形材料的相关计算。该软件还集成了多项额外功能，包括分子极化率张量计算、分子极化率对标参考值拟合、多种感应能量计算方案，以及将感应能量外推至体相极限的功能。研发团队特别注重其与其他软件包的互操作性，因此Polar Shift可从pdb、mol2乃至二进制dcd文件等多种主流文件格式中获取所需输入数据。该软件基于消息传递接口（MPI）标准实现并行化，可适配共享内存与分布式内存等多种计算机架构。本文选取八种典型有机电子学材料测试案例对Polar Shift进行了测试验证，展示了其计算能力，并将计算结果与已有文献报道数据进行了对比。