How Bond Length Alternation and Thermal Disorder Affect the Optical Excitation Energies of π-Conjugated Chains: A Combined Density Functional Theory and Molecular Dynamics Study

详细信息    查看全文

• 作者：Juliana Bois ; Thomas Körzdörfer
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2016
• 出版时间：April 12, 2016
• 年：2016
• 卷：12
• 期：4
• 页码：1872-1882
• 全文大小：709K
• 年卷期：0
• ISSN：1549-9626

文摘

We dissect the sources of error leading to inaccuracies in the description of the geometry and optical excitation energies of π-conjugated polymers. While the ground-state bond length alternation is shown to be badly reproduced by standard functionals, the recently adapted functionals PBEh* and ωPBE* as well as the double hybrid functional XYGJ-OS manage to replicate results obtained at the CCSD(T) level. By analysis of the bond length alternation in the excited state, a sensitive dependence of the exciton localization on the long-range behavior of the functional and the amount of Hartree–Fock exchange present is shown. Introducing thermal disorder through molecular dynamics simulations allows the consideration of a range of thermally accessible configurations of each oligomer, including trans to cis rotations, which break the conjugation of the backbone. Thermal disorder has a considerable effect when combined with functionals that overestimate the delocalization of the excitation, such as B3LYP. For functionals with a larger amount of exact exchange such as our PBEh* and ωPBE*, however, the effect is small, as excitations are often localized enough to fit between twists in the chain.