Browsing by Subject "Density-functional-theory"

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    Anionic dependency of electronic and nonlinear optical properties of ionic liquids
    (Elsevier B.V., 2022) Bardak F.; Bardak C.; Karaca C.; Kose E.; Bilgili S.; Atac A.
    Nonlinear optical phenomena play significant roles in the bulk properties and responsive characteristics of ionic liquids, especially when used under strong electric fields. The variability of the anion-cation pair in ionic liquids makes them designer solvents; thus, the anion or cation dependency of the physicochemical properties should be understood in depth. Accordingly, the electric field-induced characteristics of eight ionic liquids with [Br]−, [BF4]−, [PF6]−, [Ac]−, [TFAc]−, [MS]−, [NTf2]−, and [Tos]− anions paired with the 1-butyl-3-methyl imidazolium cation were investigated using density functional theory modeling at four theoretical levels: B3LYP-6-31G(d), M06-2X 6-31G(d), M06-2X 6-311++G(d,p), and M06-2X aug-cc-PVTZ. The frontier molecular orbitals, electrostatic potential surface, and electron density difference maps were obtained to visualize the electrostatic characteristics. The permanent electric dipole moment, linear electric polarizability, and first-order and second-order hyperpolarizabilities were also determined. While the static dipole moment and dipole polarizabilities could be obtained using low-level quantum chemistry at a satisfactory level, the functionalization of more intensive methods was required to accurately obtain the nonlinear optical properties. © 2021 Elsevier B.V.
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    Investigation of the interionic interactions and spectroscopic features of 1-Octyl-3-methylimidazolium chloride, tetrafluoroborate, and hexafluorophosphate ionic liquids: An experimental survey and DFT modeling
    (Elsevier B.V., 2022) Bilgili S.; Bardak F.; Kose E.; Atac A.
    This study presents the spectroscopic and electronic properties of some imidazole-based ionic liquids (ILs) consisting of 1-Octyl-3-methylimidazolium cation and chloride, tetrafluoroborate, and hexafluorophosphate anions from experimental and theoretical perspectives. The ground state structural and vibrational characteristics of the ionic liquids have been achieved through Density Functional Theory (DFT) calculations at the Becke's and the Lee–Yang–Parr (B3LYP) and 6–311++G(d,p) level of theory in Gaussian 16. The electronic and magnetic features of the ILs have been examined by using electronic absorption spectra and Nuclear Magnetic Resonance spectroscopy (NMR) techniques along with the calculations from Time-Dependent Density Functional Theory (TD-DFT) and using Gauge-Including Atomic Orbital (GIAO) method. The intra- and interionic noncovalent interactions in the ionic liquids have been revealed via the electron density analysis based on the Atoms in Molecules (AIM) approach, and decomposed as hydrogen bonding, van der Waals interactions, and steric effects via Reduced Density Gradient (RDG) analysis. To gain insight into the possible effects of anion-cation interaction on the physicochemical properties of ionic liquids, interionic interactions, reactivity properties, topological critical points, and electrostatic potential surfaces were obtained. These interactional characteristics were interpreted in terms of both the anion dependency and interaction type. Notably, the results of this study were evaluated together with the results obtained from our previous study on ILs consisting of the same anions with the 1-Hexyl-3-methylimidazolium cation to achieve the effects of the extension in the chain length of the cation in the presence of the same anion on the spectroscopic and electronic properties of ionic liquids. © 2022 Elsevier B.V.
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    External field intensity and wavelength dependency from IR to deep UV of linear and nonlinear optical properties of 1-butyl-3-methylimidazolium dicyanamide ionic liquid
    (Elsevier B.V., 2023) Bardak F.; Bardak C.
    The electronic structure, inter-ionic interactions and charge transfer, polarizability, and first-order and second-order hyperpolarizabilities of 1-butyl-3-methylimidazolium dicyanamide ionic liquid have been explored via modeling at M06-2X/6-311++G(d,p) level of theory. External field intensity dependence of electronic properties was investigated by utilization of field intensity from 0.0001 to 0.002 au applied in the direction of anion-cation. Interionic interactions have been characterized through the reduced density gradient method to reveal and distinguish hydrogen bonding and other non-covalent interactions. Extraordinary bonding interactions were observed between the anion and ring system of the cation. Electronic excitation characteristics were analyzed based on the inter-fragment charge transfer method to distinguish charge transfer contributions from local excitations. Static and dynamic nonlinear optical parameters namely the total dipole moment μ, the mean polarizability α(0,0) and α(−ω; ω), the anisotropy of polarizability Δα(0,0) and Δα(−ω; ω) the first hyperpolarizability in the direction of dipole moment β(0,0,0), β(−ω; ω,0), and β (−2ω; ω,ω), the average second hyperpolarizability γ(0;0,0,0), γ(−ω; ω,0,0) and γ(−2ω; ω,ω,0) have been calculated for specific laser wavelengths corresponding to the UV, visible, and infrared region. Thus, a novel way of mapping the field intensity and wavelength dependence of NLO properties was achieved. The hyperpolarizability calculations indicate that 1-butyl-3-methylimidazolium dicyanamide has a significant potential to be used in electro-optics Pockels effect, second-harmonic generation, and electro-optical Kerr effect applications. NLO property maps indicate that the wavelength dependence in the IR and visible region is almost ignorable when compared with that of the UV region where the first hyperpolarizabilities can increase by ten thousand and the second hyperpolarizabilities can reach up to ten billion times. © 2023 Elsevier B.V.