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Generalized gradient approximation exchange energy functional with near-best semilocal performance
摘要： We develop and validate a non-empirical generalized gradient approximation (GGA) exchange (X) density functional which performs as well as the SCAN meta-GGA on standard thermochemistry tests. Additionally, the new functional (“NCAP”) yields Kohn-Sham eigenvalues that are useful approximations of the density functional theory (DFT) ionization potential theorem values by inclusion of a systematic derivative discontinuity shift of the X potential. NCAP also enables time-dependent DFT (TD-DFT) calculations of good quality polarizabilities, hyper-polarizabilities, and one-fermion excited states without modification (calculated or ad hoc) of the long-range behavior of the exchange potential or other patches. NCAP is constructed by reconsidering the imposition of the asymptotic correctness of the X potential (-1/r) as a constraint. Inclusion of derivative discontinuity and approximate integer self-interaction correction treatments along with first-principles determination of the effective second-order gradient expansion coefficient yields a major advance over our earlier correct asymptotic potential functional [“CAP”; J. Chem. Phys. 142, 054105 (2015)]. The new functional reduces a spurious bump in the CAP atomic exchange potential and moves it to distances irrelevantly far from the nucleus (outside the tail of essentially all practical basis functions). It therefore has nearly correct atomic exchange-potential behavior out to rather large finite distances r from the nucleus but eventually goes as ? c / r with an estimated value for the constant c of around 0.3, so as to achieve other important properties of exact DFT exchange within the restrictions of the GGA form. We illustrate the results with the Ne atom optimized effective potentials and with standard molecular benchmark test data sets for thermochemical, structural and response properties.
关键词： hyperpolarizabilities,excitation energies,Density functional theory,exchange potential asymptotic behavior,polarizabilities,exchange-correlation functional
更新于2025-09-23 15:21:21
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A statistical description of scattering at the quantum level
摘要： Quantum physics is undoubtedly the most successful theory of the microscopic world, yet the complexities which arise in applying it even to simple atomic and molecular systems render the description of basic collision probabilities a formidable task. For this reason, approximations are often employed, the validity of which may be restricted to given energy regimes and/or targets and/or projectiles. Now we have found that the lognormal function, widely used for the probability distribution of macroscopic stochastic events (as diverse as periods of incubation of and recovery from diseases, size of grains, abundance of species, fluctuations in economic quantities, etc.) may also be employed to describe the energy dependence of inelastic collisions at the quantum level (including ionization, electron capture and excitation by electrons, positrons, protons, antiprotons, etc.), by allowing for the relevant threshold energy. A physical interpretation is discussed in this article by analogy with the heat capacity of few-level systems in solid state physics. We find the generality of the analysis to extend also to nuclear reactions. As well as aiding the description of collision probabilities for quantum systems, this finding is expected to impact also on the fundamental understanding of the interface between the classical and quantum domains.
关键词： ionization,electron capture,nuclear reactions,lognormal distribution,excitation,inelastic collisions,quantum physics
更新于2025-09-23 15:21:21
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Plasmon excitation and subsequent isomerization dynamics in naphthalene and azulene under fast proton interaction
摘要： The interaction of fast protons (velocity between 1.41 and 2.4 a.u.) with naphthalene and azulene is investigated as a model of an ion-polycyclic aromatic hydrocarbon interaction system. Production of various intact and fragment ions in coincidence with electron emission, electron transfer to projectile, or both is analyzed. The two targets being isomers, the rather obvious similarity in the fundamental ion-molecule collision energetics is quantitatively verified. The fast isomerization processes of cationic azulene are observed to be influencing its further dissociation channels such as C2H2 and H eliminations. A first ever attempt is presented here wherein single plasmon excitation in conjunction with isomerization dynamics is reported. Evidence from dication evaporation energetics is used to invoke the double plasmon excitation model. A model based on the multiplasmon resonance explains the observed proton velocity dependence of double to single ionization cross sections. Moreover an attempt is made to reinforce the proposition of double plasmon excitation by explaining the observed suppression of neutral H loss from dications as opposed to monocations.
关键词： double plasmon excitation,isomerization dynamics,naphthalene,azulene,ion-polycyclic aromatic hydrocarbon interaction,plasmon excitation,fast protons
更新于2025-09-23 15:21:01
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Pulsed interleaved excitation-based line-scanning spatial correlation spectroscopy (PIE-lsSCS)
摘要： We report pulsed interleaved excitation (PIE) based line-scanning spatial correlation spectroscopy (PIE-lsSCS), a quantitative fluorescence microscopy method for the study of dynamics in free-standing lipid bilayer membranes. Using a confocal microscope, we scan multiple lines perpendicularly through the membrane, each one laterally displaced from the previous one by several ten nanometers. Scanning through the membrane enables us to eliminate intensity fluctuations due to membrane displacements with respect to the observation volume. The diffusion of fluorescent molecules within the membrane is quantified by spatial correlation analysis, based on the fixed lag times between successive line scans. PIE affords dual-color excitation within a single line scan and avoids channel crosstalk. PIE-lsSCS data are acquired from a larger membrane region so that sampling is more efficient. Moreover, the local photon flux is reduced compared with single-point experiments, resulting in a smaller fraction of photobleached molecules for identical exposure times. This is helpful for precise measurements on live cells and tissues. We have evaluated the method with experiments on fluorescently labeled giant unilamellar vesicles (GUVs) and membrane-stained live cells.
关键词： lipid bilayer membranes,dual-color excitation,live cells,line-scanning spatial correlation spectroscopy,fluorescence microscopy,tissues,GUVs,confocal microscope,photobleaching,Pulsed interleaved excitation
更新于2025-09-23 15:21:01
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Laser Optoacoustic Method for Measurement of Light Extinction Coefficient and Investigation of Its Spatial Distribution in Colloidal Media
摘要： In the present work, the method which allows investigating the spatial distribution of light extinction coefficient in colloidal media is experimentally realized. The proposed method is based on the dependence of temporal profiles of excited OA-signals on the absorption and extinction coefficients of the studied medium. Water-based and kerosene-based magnetic fluids with volume content of magnetite particles in the range 0.35–3.5 % were studied as an example of the medium with spatially non-uniform optical properties. The capability of the reconstruction of the one-dimensional spatial distribution for the light extinction coefficient in the investigated media is demonstrated. It was shown that the relative change of the extinction coefficient with depth depends on volume concentration of magnetite particles, type of acoustical boundary and properties of carrier liquids. In the case of acoustical rigid boundary of magnetic fluid, an additional induced anisotropy occurs, which leads to increasing of the light extinction coefficient with depth in comparison with acoustical free boundary of fluid.
关键词： Laser optoacoustic method,Concentration,Magnetite particles,Thermo-optical excitation,Magnetic fluids,Structural inhomogeneities,Light extinction,Colloidal medium
更新于2025-09-23 15:21:01
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Stress-Controlled Frequency Tuning and Parametric Amplification of the Vibrations of Coupled Nanomembranes
摘要： Noninvasive tuning of the mechanical resonance frequencies of suspended parallel nanomembranes in various monolithic arrays is achieved by piezoelectric control of their tensile stress. Parametric amplification of their thermal fluctuations is shown to be enhanced by the piezoelectric actuation and amplification factors of up to 20 dB in the sub-parametric oscillation threshold regime are observed.
关键词： nanomembrane resonators,piezoelectrical actuation,parametric excitation,stress engineering
更新于2025-09-23 15:21:01
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Unseeded velocimetry in nitrogen for high-pressure, cryogenic wind tunnels: part III. Resonant femtosecond-laser tagging
摘要： Selective two-photon absorptive resonance femtosecond laser electronic excitation tagging (STARFLEET) velocimetry is characterized for the first time at high-pressure, low-temperature conditions. Studies were carried out in the NASA Langley Research Center’s 0.3 meter transonic, cryogenic wind tunnel, with flow conditions spanning the entire operational envelope of the facility; total pressures ranging from 100 kPa to 517 kPa, total temperatures from 80 K to 327 K, and Mach numbers from 0.2 to 0.85. STARFLEET signal intensity and lifetime measurements are examined for their thermodynamic dependencies since both intensity and lifetime have implications for measurement precision. Signal intensity is found to be inversely proportional to density, while lifetime scales nearly linearly with density until approaching the liquid-vapor saturation point of nitrogen. The velocity measurement accuracy and precision are assessed over the full domain of conditions, and standard error was determined to be 1.6%, while precision ranged from roughly 1.5% to 10% of the freestream velocity. The precision was also observed to have a temperature dependence, likely a result of the longer lifetimes experienced at higher densities.
关键词： femtosecond laser,resonant excitation,molecular tagging velocimetry
更新于2025-09-23 15:21:01
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Charge and dielectric response to terahertz pulses in the charge-ordered phase of
摘要： We investigated the dielectric properties of the charge-ordered phase of α-(BEDT-TTF)2I3 using exact numerical calculations of an extended Hubbard model. The electronic contribution to the electric polarization (electronic polarization) ˉP of the charge-ordered ground state is obtained by directly calculating the current when transfer integrals were changed adiabatically from symmetric integrals to integrals for the charge-ordered phase without inversion symmetry. The angle of ˉP from the positive b axis is 36?, which is consistent with experimental results and previous theoretical results based on density-functional theory. Furthermore, we numerically calculated the dynamics induced by terahertz- (THz-) pulse excitation. Both the THz-pulse-induced variation of the electronic polarization magnitude and that of the charge disproportionation that shows the charge-order amplitude are largest when the electric field of the THz pulse and ˉP have almost the same direction. This originates from the charge transfer through bond b2(cid:3) being dominant in both the adiabatic flow of the current and the THz-pulse excitation. These results reproduce important features of the experimental results of THz-pulse-induced dynamics.
关键词： charge-ordered phase,ferroelectricity,extended Hubbard model,THz-pulse excitation,electronic polarization
更新于2025-09-23 15:21:01
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[ASME ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - Quebec City, Quebec, Canada (Sunday 26 August 2018)] Volume 8: 30th Conference on Mechanical Vibration and Noise - Piezoelectric Nonlinear Energy Sink for Energy Harvesting With Rectifying DC Interface Circuit
摘要： In order to improve the performance of vibration energy harvesters over a broad frequency range, this paper proposes a use of piezoelectric nonlinear energy sink (NES) for energy harvesting from ambient vibrations. A standard rectifying direct current (DC) interface circuit is considered to generate DC power from the piezoelectric NES under harmonic excitation. Harmonic balance method is used to obtain the dynamic response and energy harvesting performance of the proposed piezoelectric NES, verified by the equivalent circuit simulation. Analytical and numerical results show that the design, by applying NES, improves the efficiency of energy harvesting without increasing the vibration of the primary structure in a broadband manner. The effects of the electromechanical coupling, excitation level and load resistance on the magnitude and bandwidth of the output DC power are investigated.
关键词： harmonic excitation,rectifying DC interface circuit,piezoelectric,energy harvesting,nonlinear energy sink
更新于2025-09-23 15:21:01
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exposed to an intense laser pulse
摘要： We investigate the role of the rotational excitation in the coherent and unidirectional B 2Σ+u emission of N2+ at 391 nm called air lasing generated when N2 is irradiated with intense femtosecond near-infrared laser pulses at 800 nm. We simulate the time-dependent population transfer process of N2+, which is assumed to be generated suddenly in an intense ultrashort laser pulse, by including vibrational and rotational degrees of freedom, and reveal that, when the light field intensity is below ≈ 4 × 1014 W cm?2, the population inversion can be achieved in N2+ only between rotationally highly excited levels in the vibrational ground (v' = 0) state of the B 2Σ+u state and those in the vibrational ground (v'' = 0) state of the electronic ground X 2Σ+g state, so that the lasing at 391 nm is realized even when the total population in the v' = 0 state of the electronically excited B 2Σ+u state is not inverted with respect to the total population in the v'' = 0 state of the electronic ground X 2Σ+g state.
关键词： air lasing,N2+,rotational excitation,population inversion,femtosecond laser pulses
更新于2025-09-23 15:21:01