基于Wannier函数的非正交修正Pulay力约束DFT在石墨烯吸附并五苯重组效应中的应用
Wannier-function-based constrained DFT with nonorthogonality-correcting Pulay forces in application to the reorganization effects in graphene-adsorbed pentacene
摘要：
在电子结构计算中，当使用由随其主体原子移动的定域轨道组成的基组时，海尔曼-费曼力中出现了普雷项。如果系统的总能量依赖于由多个原子的定域轨道定义的子空间布居，那么由于轨道非正交性随离子平移的变化，将出现非常规的Pulay项。在这里，我们推导出所需的精确表达式，这些条款，不能消除轨道正交归一化。我们已经实现了这些校正的离子力的线性标度密度泛函理论（DFT）包ONETEP，并已使用约束DFT计算的重组能量吸附在石墨烯片上的并五苯分子。计算包括系综DFT，周期性边界条件的修正，和经验范德华相互作用。对于这个系统，我们发现，张量不变的人口分析产生的吸附质子空间人口是非常接近整数值时，基于非正交Wannier函数，也但不太精确时，使用伪原子函数。因此，轨道可以为约束DFT提供非常有效的布居分析。我们的计算表明，吸附的并五苯的重组能通常低于并五苯在气相中。我们把这种效应归因于空间位阻。
英文摘要：
Pulay terms arise in the Hellman-Feynman forces in electronic structure calculations when one employs a basis set made of localized orbitals that move with their host atoms. If the total energy of the system depends on a subspace population defined in terms of the localized orbitals across multiple atoms, then unconventional Pulay terms will emerge due to the variation of the orbital nonorthogonality with ionic translation. Here, we derive the required exact expressions for such terms, which cannot be eliminated by orbital orthonormalization. We have implemented these corrected ionic forces within the linear-scaling density functional theory (DFT) package ONETEP, and have used constrained DFT to calculate the reorganization energy of a pentacene molecule adsorbed on a graphene flake. The calculations are performed by including ensemble DFT, corrections for periodic boundary conditions, and empirical Van der Waals interactions. For this system we find that tensorially invariant population analysis yields an adsorbate subspace population that is very close to integer-valued when based upon nonorthogonal Wannier functions, and also but less precisely when using pseudoatomic functions. Thus, orbitals can provide a very effective population analysis for constrained DFT. Our calculations show that the reorganization energy of the adsorbed pentacene is typically lower than that of pentacene in the gas phase. We attribute this effect to steric hindrance.
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