Influence of Alkali Metal Doping and BN Substitution on the Second-Order Nonlinear Optical Properties of Graphyne: A Theoretical Perspective

Abstract

The electronic and nonlinear optical (NLO) properties of BN-substituted graphynes and the corresponding alkali-doped hybrid systems have been determined using density functional theory. When the carbon atoms in the graphyne are replaced by BN pairs, the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap (E gap) increases to some extent, and the static first hyperpolarizabilities (β0) of the novel systems hardly increase. However, when an alkali atom is introduced on the surface of BN-substituted graphyne, the doping effect can effectively modulate the electronic and NLO properties. Doping the alkali atom can significantly narrow the wide E gap of BN-substituted graphynes in the range of 1.03–2.03 eV. Furthermore, the doping effect brings considerable β0 values to these alkali-doped systems, which are 52–3609 au for Li-doped systems and 3258–211 053 au for Na/K-doped ones. The result reveals that the β0 values of alkali-doped complexes are influenced by the atomic number of alkali metals and the proportion of BN pairs. The nature of the excellent NLO responses of alkali-doped complexes can be understood by the low excitation energy of the crucial excited state and the analysis of the first hyperpolarizability density. Besides, these alkali-doped complexes have a deep-ultraviolet working region. Therefore, the combined effect of alkali metal doping and BN substitution can be an excellent strategy to design novel high-performance NLO materials based on graphyne.

Ab Initio Dynamics of Graphene and Graphyne Electrodes in Vacuum and in the Presence of Electrolytes

“…Several computational and experimental studies characterizing the structural and energetic properties of graphyne and exploring its applications have been published recently. − In particular, computational studies based on static DFT calculations and/or classical molecular dynamics simulations have provided a precious volume of information about these systems. − Work involving its electronic structure as well as the changes produced by substitutional groups, functionalization, or adsorption of ions has been extensively carried out. ,,,,− Despite this vast volume of information, little is known about the intramolecular dynamics of these materials and the interaction of their electronic density with condensed media. In this work, we obtain this information through ab initio molecular dynamics (AIMD) simulations in which we investigate the structural, spectroscopic, and electronic properties of a graphyne electrode in contact with an ionic liquid (EMIM-BF 4 ), which is a typical electrolyte in electrochemical applications.…”

“…This acetylene group separates graphene’s hexagonal rings, giving it unique mechanical and electronic properties, as well as an extensive set of advantageous physical and chemical properties that make them useful for applications in many fields, such as catalysis, sensor, and transistor technologies, and energy storage . In particular, properties such as large interlayer distance, unique porous structure, large specific surface area, intrinsic band gap, high electrochemical capacity, and high conductivity are highly desirable for electrochemical energy storage applications. − Single-layer γ-graphyne, which is the most common type of graphyne, has been characterized as a moderate gap semiconductor, which allows very high electron mobility compared to graphene, in addition to high thermal conductivity and large mechanical strength. − Because of these properties, γ-graphyne has been investigated to form the basis for next-generation carbon-based energy devices …”