Molecular dynamics simulations are used to investigate the aggregation of the cross-contacted and non-cross-contacted graphene sheets in n-hexane, 2,3-dimethylbutane, and cyclohexane solvents. The ...results show that the main driving force of the graphene aggregation is the interaction between the graphene sheets, and the interaction between solvent molecules also contributes to the aggregation slightly. The initial graphene configurations and the solvent molecule structures both have effects on the graphene aggregation speed. Specifically, the cross-contacted graphene sheets aggregate faster than the non-cross-contacted configuration, since the interaction between the graphene sheets is larger and the direction of this interaction is conducive to pushing away the solvent molecules adsorbed on the graphene surface. The graphene aggregation speed is larger in n-hexane mainly since the mobility of the solvent molecules is higher than the other two solvents, while the interaction between graphenes/solvents has little influence for the systems used in this work. This work provides useful insights into the graphene aggregation in the solvents with different initial graphene configurations and solvent molecule structures.
Graphical abstract
The potential astronomical interest dithioformic acid (
trans
-HC(= S)SH) exists five isomers and has received considerable attention of astronomical observation in recent years. The different ...positions of H atoms of five isomers lead to diverse point groups, dipole moments, and spectroscopic constants. The anharmonic force field and spectroscopic constants of them are calculated using CCSD(T) and B3LYP employing correlation consistent basis sets. Molecular structures, dipole moments, rotational constants, and fundamental frequencies of
trans
-HC(= S)SH are compared with the available experimental data. The B3LYP/Gen = 5 and CCSD(T)/Gen = Q results can reproduce them well. Molecular structures, dipole moments, relative energies, spectroscopic constants of
cis
-HC(= S)SH, and dithiohydroxy carbene (DTHC) are also calculated. The new data obtained in this study are expected to guide the future high resolution experimental work and to assist astronomical search for CH
2
S
2
.
In this contribution, we report a computational study of the vibrational Resonance Raman (vRR) spectra of cytosine in water, on the grounds of potential energy surfaces (PES) computed by ...time-dependent density functional theory (TD-DFT) and CAM-B3LYP and PBE0 functionals. Cytosine is interesting because it is characterized by several close-lying and coupled electronic states, challenging the approach commonly used to compute the vRR for systems where the excitation frequency is in quasi-resonance with a single state. We adopt two recently developed time-dependent approaches, based either on quantum dynamical numerical propagations of vibronic wavepackets on coupled PES or on analytical correlation functions for cases in which inter-state couplings were neglected. In this way, we compute the vRR spectra, considering the quasi-resonance with the eight lowest-energy excited states, disentangling the role of their inter-state couplings from the mere interference of their different contributions to the transition polarizability. We show that these effects are only moderate in the excitation energy range explored by experiments, where the spectral patterns can be rationalized from the simple analysis of displacements of the equilibrium positions along the different states. Conversely, at higher energies, interference and inter-state couplings play a major role, and the adoption of a fully non-adiabatic approach is strongly recommended. We also investigate the effect of specific solute-solvent interactions on the vRR spectra, by considering a cluster of cytosine, hydrogen-bonded by six water molecules, and embedded in a polarizable continuum. We show that their inclusion remarkably improves the agreement with the experiments, mainly altering the composition of the normal modes, in terms of internal valence coordinates. We also document cases, mostly for low-frequency modes, in which a cluster model is not sufficient, and more elaborate mixed quantum classical approaches, in explicit solvent models, need to be applied.
► Using density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations, we have found that the most stable positions of Cs adatoms on ...(2×2)GaN(0001) surface are at N-bridge and H3 sites for 1/4 monolayer coverage. ► The change of adsorption energies and the change of work function with coverage from 1/4 to 1 monolayer are analyzed, and the reason for those changes is also analyzed. ► These results provide a theoretical reference for the activation experiment of negative electron affinity GaN optoelectronic cathodes.
The adsorption characteristics and change in work function of Cs on a (2×2) GaN(0001) surface with a coverage from 1/4 to 1 monolayer (ML) have been investigated using density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations. The results show that the most stable positions of Cs adatoms on GaN(0001) surfaces are at N-bridge and H3 sites for 1/4 ML coverage. As the Cs atomic coverage is increased, adsorption energy and stability reduce and achieve saturation when the Cs adatom coverage is 3/4 ML. The transfer of Cs6s electrons to Ga atoms in the outermost layer decreases the work function of the system.
In this work, we present the theoretical study of the vibrationally resolved absorption (ABS), electronic circular dichroism (ECD), emission (EMI), and circularly polarized luminescence (CPL) spectra ...of a boron-fused double helicene, with a detailed and complete discussion of the alternative possible approximate methods. Given the fact that few examples of CPL calculations exist, the potential energy surfaces (PESs) have been constructed and compared with Adiabatic (AH) and Vertical Hessian (VH) models. All the vibronic calculations have accounted for Duschinsky mixings, Franck-Condon (FC) effect and Herzberg-Teller (HT) contribution. Moreover, different HT expansions have been checked and compared, by computing the derivatives of the electric and magnetic dipole transition moments around the equilibrium geometries of the initial and final states. Our results show that both AH and VH models have well reproduced the experimental vibronic structures and VH model shows a better performance in the simulation of spectral lineshapes. They also show that HT effects dominate the shapes of EMI and CPL, tuning the relative heights of the different vibronic peaks, improving the agreement with the experiment for EMI. Moreover, HT effects are the main reason for the mirror-symmetry breaking between ECD and CPL spectra. Furthermore, interesting interference effects between FC and HT contributions have also been addressed.
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•Vibrationally Resolved Electronic Circular Dichroism and Circularly Polarized Luminescence have been investigated.•Herzberg-Teller (HT) effects improve the performance by tuning the relative heights of vibronic bands.•HT effects explain the mirror-symmetry breaking down between absorptive and emissive chiroptical spectroscopies.
Context
The cyano propargyl radical (CH
2
C
3
N and HC
3
HCN) is important reaction intermediate in both combustion flames and extraterrestrial environments such as cold molecular clouds and ...circumstellar envelopes of carbon stars. The acquisition of spectroscopic constants and anharmonic effect facilitates a more in-depth study of this radical. However, the data available in the literature do not allow the precise predictions for it in the interstellar medium. In this work, complete spectroscopic parameters as well as anharmonic constants of two radicals of C
4
H
2
N have been evaluated by different DFT methods. The calculated results show that it is reasonable to study the molecular spectroscopic properties of C
4
H
2
N by wB97XD/6-311++G theoretical level. On this basis, the sextic centrifugal distortion constants, anharmonic constants, vibration-rotation interaction constants, and so on are predicted for the study of high-precision rovibrational spectrum. In addition, the relationship between the anharmonic effect and vibration mode of CH
2
C
3
N and HC
3
HCN and their infrared spectroscopic characteristics are discussed.
Methods
The calculation of the anharmonic force fields and spectroscopy properties was performed using B3LYP, B3PW91, CAM-B3LYP, and wB97XD methods combined with the 6-311++G and aug-ccpVTZ basis sets, respectively, by the Gaussian16 program suite. The IR spectra were performed with Multiwfn3.8.
This work presents a systematic investigation of the spectroscopic properties at anharmonic force fields of ground electronic state (
X
˜
1
A
1
) of LiNH
2
, which are calculated using second-order ...Møller-Plesset perturbation theory (MP2) and density functional theory (DFT) with hybrid GGA and meta-hybrid GGA (M06-2X) exchange-correlation functional. Two high angular momentum basis sets of 6-311+g (2d, p) and 6-311++g (3df, 2pd) are used. The equilibrium geometries, ground-state rotational constants, harmonic frequencies, and quartic and sextic centrifugal distortion constants of LiNH
2
are calculated and compared with corresponding experimental or theoretical data. The predicted accuracy of the calculated constants has been confirmed by analyzing the deviations with respect to experiment. In addition, the anharmonic constants, vibration-rotation interaction constants, force constants, and Coriolis coupling constants of LiNH
2
are firstly obtained. The infrared spectrum is predicted and together with the first prediction on the higher-order anharmonic constants contributes to a better understanding of the vibrational and rotational characteristics of LiNH
2
, thus revealing its internal structure.
Graphical abstract
The IR spectra and the magnified IR spectra at 3500 cm
−1
in harmonic approximations of LiNH
2
using B3P86, M06-2X and MP2 methods combining with 6-311++g(3df,2pd)
The concerted mechanisms of excited state intramolecular proton transfer (ESIPT) of bis-2,4-(2-benzoxazolyl)-hydroquinone (BBHQ′) and its derivatives (BBHQ′– and DHBO′) have been investigated using ...the density functional theory (DFT) and the time-dependent density functional theory (TDDFT). The calculated absorption and emission spectra of BBHQ′ and its derivatives are in good agreement with the experimental results. The calculated bond lengths, bond angles, and IR vibrational spectra linked with hydrogen bond of molecular BBHQ′ in the S0 and S1 states demonstrate that the hydrogen bond is strengthened in the S1 state. Compared to BBHQ′, BBHQ′– has a weak change of hydrogen bond between the S1 and S0 states. The calculation results show that there are three stable structures of BBHQ′ in the S1 state. We find that the structure corresponding to the 481 nm fluorescence spectrum corresponds to BBHQ′-A rather than BBHQ′–-K (Tetrahedron Lett., 2016, 57, 3518). The calculated frontier molecular orbitals (MOs) indicate the nature of the charge distribution and the trend of proton transfer of BBHQ′-A. The constructed potential energy surfaces of BBHQ′ and DBHO′ further elucidate the proposed mechanism that one-proton or two-proton transfer can happen (stepwise or synchronous) in the S1 states. The proposed ESIPT mechanism can provide a good explanation of the phenomenon of fluorescence quenching of BBHQ′ and its derivatives. Finally, the weak interaction types are discriminated through the reduced density gradient (RDG) analyses of BBHQ′ and BBHQ′–.
The present graph shows the electron momentum distribution of vibronic effect and equilibrium geometry. In contrast with the equilibrium geometry, there are four vibrational modes (v9, v3, v2, v7 in ...sequence) can significantly affect the electron momentum distribution. These four all can change the symmetry spatial geometry that will further affect the electron cloud. In addition, the ratio of charge transfer of 12 molecular vibrational modes also shows alike sequence as the above graph, i.e. the vibration caused symmetry-broken effect influences the electron momentum spectroscopy of core orbitals.
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•The symmetry-broken effects induced by nuclear vibrations.•Electron momentum spectroscopy of core electrons.•A new methodology based on quantum mechanics considers nuclear vibrations.
The vibronic coupling effect is usually studied by invoking the breakdown of Born-Oppenheimer approximation. The present study shows that the symmetry-broken effect induced by nuclei vibrations can also lead strong impact on the electronic states under the framework of Born-Oppenheimer approximation. This adiabatic-invoking vibrational effect on electron momentum spectroscopy of ethylene (C2H4), ethane (C2H6) and methanol (CH3OH) was studied with quantum mechanical method. The results show that electron momentum spectroscopy of localized electrons, especially core electrons in axial symmetric geometry molecules can be affected unusually and strongly by several asymmetric vibrational modes.
In this work, we used multi-scale computational simulation methods combined with density functional theory (DFT) and finite element analysis (FEA) in order to study the optical properties of ...substitutional doped aluminium nitride (AlN). There was strong surface plasmon resonance (SPR) in the near-infrared region of AlN substituted with different alkali metal doping configurations. The strongest electric field strength reached 10
V/m. There were local exciton and charge transfer exciton behaviours in some special doping configurations. These research results not only improve the application of multi-scale computational simulations in quantum surface plasmons, but also promote the application of AlN in the field of surface-enhanced linear and non-linear optical spectroscopy.
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