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XYG3-type doubly hybrid (xDH) approximations have gained widespread recognition for their accuracy in describing a diverse range of chemical and physical interactions. However, a recent study [Song et al., J. Phys. Chem. Lett. 12, 800–807 (2021)] has highlighted the limitation of xDH methods in calculating the dissociation of NaCl molecules. This issue has been related to the density and orbitals used for evaluating the energy in xDH methods, which are obtained from lower-rung hybrid density functional approximations (DFAs) and display substantial density errors in the dissociation limit. In this work, we systematically investigate the influence of density on several challenging datasets and find that xDH methods are less sensitive to density errors compared to semi-local and hybrid DFAs. Furthermore, we demonstrate that the self-interaction corrected SCAN density approach offers superior accuracy compared to the self-consistent SCAN density and Hartree–Fock density approaches, as evidenced by performing charge analysis on the dissociation of heterodimers, such as NaCl and LiF. Building on these insights, we propose a five-parameter xDH method using the SCAN density and orbitals corrected by the PZ-SIC scheme. This new xDH@SCAN(SIC) method provides a balanced and accurate description across a wide range of challenging systems. [ABSTRACT FROM AUTHOR]

Increasing carrier injection efficiency is an important way to improve the performance of organic light-emitting diodes (OLEDs). In this work, self-assembled monolayers (SAMs) were formed on indium tin oxide (ITO) anodes with different aromatic carboxylic acids. The relationship between the molecular structure and its effect on modification was investigated. The presence of monolayers was verified by X-ray photoelectron spectroscopy. Water contact angle tests show that the surface energy of ITO has decreased after SAM modification which is beneficial to obtain a flat film of organic functional materials on ITO. In addition, the data of ultraviolet photoelectron spectroscopy reveal that the work function of SAM-ITO with different molecules modified has increased to varying degrees. Therefore, a no-hole injection layer (HIL) device whose structure is ITO/SAMs/α-naphthyphenylbiphenyldiamine (NPB) (25 nm)/tris(8-hydroxyquindino) aluminum (III) (Alq3) (60 nm)/LiF (1 nm)/Al (100 nm) was designed to explore the impact of SAMs on OLEDs. OLED performance shows SAMs of 9H-carbazole-2-carboxylic acid (CzCA) facilitating the device to obtain superior luminescence performance, with a turn-on voltage of 2.6 V and a maximum luminance of 30 418 cd·m−2. In order to study the mechanism, the highest occupied molecular orbital (HOMO) and other information of SAM molecules were calculated by Gaussian 09. According to the result, the HOMO of CzCA appears as a special "through-band," which is beneficial to the hole transport. It is considered that when the HOMO of the SAM molecule is in a shape favorable for hole transport, hole injection will be facilitated and the performance of the OLEDs will be improved greatly. [ABSTRACT FROM AUTHOR]