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We developed the generalized tight-binding model to study the magneto-electronic properties of AAB-stacked trilayer graphene. Three groups of Landau levels (LLs) are characterized by the dominating subenvelope function on distinct sublattices. Each LL group could be further divided into two sub-groups in which the wavefunctions are, respectively, localized at 2/6 (5/6) and 4/6 (1/6) of the total length of the enlarged unit cell. The unoccupied conduction and the occupied valence LLs in each sub-group behave similarly. For the first group, there exist certain important differences between the two sub-groups, including the LL energy spacings, quantum numbers, spatial distributions of the LL wavefunctions, and the field-dependent energy spectra. The LL crossings and anticrossings occur frequently in each sub-group during the variation of field strengths, which thus leads to the very complex energy spectra and the seriously distorted wavefunctions. Also, the density of states (DOS) exhibits rich symmetric peak structures. The predicted results could be directly examined by experimental measurements. The magnetic quantization is quite different among the AAB-, AAA-, ABA-, and ABC-stacked configurations. [ABSTRACT FROM AUTHOR]

The alkylammonium halogenocobalate families are subjected to diverse studies according to their wide field application. In this work, the [(C 3 H 7) 4 N] 2 CoBr 4 compound was synthesized using a slow evaporation solution growth method at room temperature and characterized by X-ray powder diffraction (XRPD) and UV-VIS-IR absorption spectrometry. The X-ray powder diffraction (XRPD) data confirmed the formation of a single-phase with monoclinic system (C2/c space group). The optical absorption and reflectance spectra of the named compound were measured at the range [240 nm–1900 nm] at room temperature. Using three methods, we have determined the direct optical band gap estimated at 3.8 eV and the Urbach energy. Different models were used to calculate the refractive index, which was found to be in the range of 2.12–2.58. This spectrum consists also of electronic transition d-d of Co2+ (3 d7) ions. This work examines a detailed crystal-field analysis of the UV–Vis–NIR lines associated to the transitions between the Stark levels of Co2+, occupying a T d site symmetry in [CoBr 4 ]2- (organic part). The theoretical study is based on the Racah tensor algebra methods. This analysis permits us to determine the electronic structure of the cobalt ion Co2+ based on the crystal field theory. As a result, Racah and crystal-field parameters have been reliably obtained. A good agreement between the theoretical and the experimental energy levels are obtained. This theoretical study confirms the T d site symmetry of Co2+ in [CoBr 4 ]2- and leads to a satisfactory correlation between experimental and calculated energy levels. In addition to internal transitions, the absorption spectrum shows vibrational peaks witness of anharmonic behavior. • Absorption and reflectance spectra were measured. • Optical band gap, Urbach energy, extinction coefficient and refractive index were determined. [ABSTRACT FROM AUTHOR]

This study reports the spectroscopic characterization and second hyperpolarizability of the odd spin states of acetonitrile at B3LYP/aug-cc-pVDZ level of theory. The spectroscopic parameters studied in gas phase and water solvent. Upon changes of spin states of acetonitrile significant changes are observed in the spectroscopic study. Natural transition orbitals (NTOs) study also reported for acetonitrile in gas phase and water solvent. From nonlinear optical study it is observed that second hyperpolarizability of odd spin states of acetonitrile are more responsive than the first hyperpolarizability. [Display omitted] • Spectroscopic study of odd spin state of acetonitrile in gas and water solvent reported. • The solvent effect taken in to the consideration for the study using IEFPCM model. • The Natural transition orbital studied for the acetonitrile in gas phase and in water solvent. • An increase in field strength decreases the HOMO to LUMO gap in gas and solvent acetonitrile. • Thorough nlo study confirmed acetonitrile is more responsive to 2nd hyperpolarizability than 1st. The present study reports the spectroscopic characterization and second hyperpolarizability of odd spin states of acetonitrile in gas phase and water solvent. The odd spin states of acetonitrile are singlet, triplet and quintet spin state of acetonitrile have been considered for the study. The spectroscopic characterization viz. energy, geometrical parameters, infrared and electronic absorption spectra, molecular orbitals (MOs) their energies and natural transitions orbitals (NTOs) in gas phase and water solvent state reported at B3LYP/aug-cc-pVDZ level of theory. The second hyperpolarizability values are obtained using various methods and basis sets for comparison. It has been observed that the second hyperpolarizability values for the odd spin states of acetonitrile are more positive than the first hyperpolarizability. It is clearly seen that the effect of spin on spectroscopic parameters except on energy. The singlet gas phase acetonitrile calculations are well matching with the available experimental determinations. The TDDFT approach has been used to study electronic absorption spectra of all spin states of acetonitrile in gas phase and in water solvent. The IEFPCM model implemented in studying acetonitrile in water solvent at B3LYP/aug-cc-pVDZ level of theory. It is observed that HOMO to LUMO gap is larger for singlet than the triplet and quintet spin state and it decrease with an increase in strength of an applied field. All these calculations performed using Gaussian 16 program package. [ABSTRACT FROM AUTHOR]

Abstract: Vibrational and electronic spectral measurements were made for 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Optimized geometrical structure and harmonic vibrational frequencies were computed by DFT(B3LYP, CAMB3LYP, B3P86, M062X, mPW3PBE and PBE1PBE) using 6-311++G(d,p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed both in gas-phase and in CH2Cl2 solution using TDCAMB3LYP/6-311++G(d,p) and PCM-TDCAMB3LYP/6-311++G(d,p) approaches, respectively, the calculated results provide a good description of positions of the bands maxima in the observed electronic spectrum. [Copyright &y& Elsevier]

Abstract: Vibrational spectral measurements were made for 1,5-dimethyl-2-phenyl-4-[(pyridin-4-ylmethylene)-amino]-1,2-dihydro-pyrazol-3-one (DPPDP). Optimized geometrical structure and harmonic vibrational frequencies were computed by ab initio RHF and DFT (B-based BP86, BLYP, BPW91, B3-based B3P86, B3LYP, B3PW91 and O3-based O3LYP) methods using 6-311++G(d,p) basis set. Complete assignments of the observed spectra were proposed. The equilibrium geometries computed by all of the methods, were compared with X-ray diffraction results. The absorption spectra of the title compound were computed both in gas phase and in CH3CN solution using TD-B3LYP/6-311++G(d,p) and PCM-B3LYP/6-311++G(d,p) approaches and the calculated results provide a good description of positions of the two band maxima in the observed electronic spectrum. [ABSTRACT FROM AUTHOR]

In this work, the effect of the position of fluorine substituents in tetrafluorosubstituted metal phthalocyanines on their vibrational spectra is studied. For this purpose the assignments of the most intense bands in IR- and Raman spectra of tetrafluorosubstituted metal phthalocyanines with F-substituents in non-peripheral positions MPcF 4 -np (M = Zn, Co, Cu, Fe, Pd, VO, Pb) were carried out on the basis of the density functional theory (DFT) calculations. The vibrational spectra of MPcF 4 -np were compared with those of the corresponding derivatives bearing F-substituents in peripheral positions (MPcF 4 -p). It was shown that similarly to MPcF 4 -p, the bands in the IR and Raman spectra of MPcF 4 -np, which are dependent on central metals, are located in the spectral range from 1350 to 1550 cm−1. The effect of the position of fluorine substituents in MPcF 4 on the electronic absorption spectra of their solution and films is also discussed. [Display omitted] [ABSTRACT FROM AUTHOR]