| 1. |
- Ahmadzadeh, Karan, et al.
(författare)
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Toward Accurate Two-Photon Absorption Spectrum Simulations: Exploring the Landscape beyond the Generalized Gradient Approximation
- 2024
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 15:4, s. 969-974
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter, we present a pioneering analysis of the density functional approximations (DFAs) beyond the generalized gradient approximation (GGA) for predicting two-photon absorption (2PA) strengths of a set of push-pull π-conjugated molecules. In more detail, we have employed a variety of meta-generalized gradient approximation (meta-GGA) functionals, including SCAN, MN15, and M06-2X, to assess their accuracy in describing the 2PA properties of a chosen set of 48 organic molecules. Analytic quadratic response theory is employed for these functionals, and their performance is compared against the previously studied DFAs and reference data obtained at the coupled-cluster CC2 level combined with the resolution-of-identity approximation (RI-CC2). A detailed analysis of the meta-GGA functional performance is provided, demonstrating that they improve upon their predecessors in capturing the key electronic features of the π-conjugated two-photon absorbers. In particular, the Minnesota functional MN15 shows very promising results as it delivers pleasingly accurate chemical rankings for two-photon transition strengths and excited-state dipole moments.
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| 2. |
- Ding, Yubin, et al.
(författare)
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Acid/Base Switching of the Tautomerism and Conformation of a Dioxoporphyrin for Integrated Binary Subtraction
- 2014
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:40, s. 12910-12916
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Tidskriftsartikel (refereegranskat)abstract
- Compared with most of the reported logic devices based on the supramolecular approach, systems based on individual molecules can avoid challenging construction requirements. Herein, a novel dioxoporphyrin DPH22 was synthesized and two of its tautomers were characterized by single-crystal X-ray diffraction studies. Compound DPH22 exhibits multichannel controllable stepwise tautomerization, protonation, and deprotonation processes through interactions with H and F- ions. By using the addition of H+ and F- ions as inputs and UVNis absorption values at.1=412, 510, 562, and 603 nm as outputs, the controlled tautomerism of DPH22 has been successfully used for the construction of an integrated molecular level half-subtractor and comparator. In addition, this acid/base-switched tautomerism is reversible, thus endowing the system with ease of reset and recycling; consequently, there is no need to modulate complicated intermolecular interactions and electron-/chargetransfer processes.
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| 3. |
- Olsen, Jogvan Magnus Haugaard, et al.
(författare)
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Dalton Project : A Python platform for molecular- and electronic-structure simulations of complex systems
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:21
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Tidskriftsartikel (refereegranskat)abstract
- The Dalton Project provides a uniform platform access to the underlying full-fledged quantum chemistry codes Dalton and LSDalton as well as the PyFraME package for automatized fragmentation and parameterization of complex molecular environments. The platform is written in Python and defines a means for library communication and interaction. Intermediate data such as integrals are exposed to the platform and made accessible to the user in the form of NumPy arrays, and the resulting data are extracted, analyzed, and visualized. Complex computational protocols that may, for instance, arise due to a need for environment fragmentation and configuration-space sampling of biochemical systems are readily assisted by the platform. The platform is designed to host additional software libraries and will serve as a hub for future modular software development efforts in the distributed Dalton community.
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| 4. |
- Li, Xin, et al.
(författare)
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Glycine in aerosol water droplets : a critical assessment of Köhler theory by predicting surface tension from molecular dynamics simulations
- 2011
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:2, s. 519-527
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol particles in the atmosphere are important participants in the formation of cloud droplets and have significant impact on cloud albedo and global climate. According to the Kohler theory which describes the nucleation and the equilibrium growth of cloud droplets, the surface tension of an aerosol droplet is one of the most important factors that determine the critical supersaturation of droplet activation. In this paper, with specific interest to remote marine aerosol, we predict the surface tension of aerosol droplets by performing molecular dynamics simulations on two model systems, the pure water droplets and glycine in water droplets. The curvature dependence of the surface tension is interpolated by a quadratic polynomial over the nano-sized droplets and the limiting case of a planar interface, so that the so-called Aitken mode particles which are critical for droplet formation could be covered and the Kohler equation could be improved by incorporating surface tension corrections.
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| 5. |
- Li, Xin, et al.
(författare)
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Paramagnetic Perturbation of the F-19 NMR Chemical Shift in Fluorinated Cysteine by O-2 : A Theoretical Study
- 2009
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Ingår i: Journal of Physical Chemistry B. - Washington, D. C. : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:31, s. 10916-10922
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined molecular dynamics and density functional theory study of dioxygen-induced perturbation of the F-19 NMR chemical shifts in an aqueous solution of fluorinated cysteine under 100 atm of O-2 partial pressure. Molecular dynamics Simulations are carried out to determine the dominant structures of O-2 and the fluorinated cysteine complexes in water, and the collected structural information is exploited in computation of F-19 chemical shifts using density functional theory. The obtained results indicate that the density redistribution of the O-2 unpaired electrons between the dioxygen and fluorinated cysteine is responsible for the experimentally observed perturbation of the F-19 NMR chemical shifts, where the Fermi contact interaction plays the key role. The O-2-induced paramagnetic F-19 chemical shift, averaged over the simulation trajectory, is comparable with the reported experimental values, proving the availability of the developed strategy for modeling F-19 NMR chemical shifts in the presence of paramagnetic agents in ail aqueous solution. The applicability of the combined molecular dynamics/density functional theory approach for dioxygen NMR perturbation to all resonating nuclei including H-1, C-13, N-15, and F-19 is emphasized, and the ramification of this for investigations of membrane protein structures is discussed.
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| 6. |
- Tang, Jun Eu, 1974, et al.
(författare)
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Microanalysis on the oxidation and sulfate attack of partially stabilized zirconia thermal barrier coating
- 2001
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Ingår i: Ceramic Engineering and Science Proceedings. - 0196-6219 .- 1940-6339. ; 22:4, s. 463-470
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Tidskriftsartikel (refereegranskat)abstract
- This aim of this investigation is to study the effect of the presence of Na2SO4 deposits and water vapor on the oxidation of an air plasma-sprayed TBC composed of a partially stabilized ZrO2 top coat with an underlying NiCoCrAlY bond coat. XRD and SEM/EDX were used to analyze the changes in the coatings after oxidation at 1000degreesC for 72 hours in dry or humidified (containing 50% H2O) O-2 atmosphere, with or without Na2SO4 deposited on the top coat. When oxidized in oxygen, bond coat oxide regions, consisting of almost pure aluminum oxide, were formed at the top coat / bond coat and bond coat / substrate interfaces and in the bond coat around the splat lines. When water vapor was present, the top coat / bond coat interface oxide was marginally thicker and included small regions with more chromium, cobalt and nickel. The addition of the salt deposits resulted in some destabilization in the outermost regions of the top coat. The salt deposits also caused the formation of thicker oxide comprising two regions, though this formation was observed only at the top coat / bond coat interface. The first type was a thin inner (i.e. bordering the bond coat) oxide that was mostly aluminum oxide. The other was a much thicker oxide containing higher levels of chromium, cobalt and nickel along with aluminum. In this oxide region, the aluminum level was higher when the chromium level was lower and vice versa.
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| 7. |
- Li, Xin, et al.
(författare)
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Re-writable multi-domain liquid crystal alignment layers through laser-induced micropatterning
- 2006
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Ingår i: Japanese Journal of Applied Physics. - 0021-4922 .- 1347-4065. ; 45:20-23, s. L591-L594
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Tidskriftsartikel (refereegranskat)abstract
- We report a method for the preparation of multi-domain liquid crystal (LC) alignment layers on polyimide surfaces with laser-induced periodic surface structures. Atomic force microscopy confirmed that the laser-induced microstructures could be easily erased and re-constructed by repeated laser exposure. The microstructures demonstrated excellent abilities to align LCs in a multi-domain way. The intricate micropatterning of LCs with high resolution was obtained. The opto-electric properties of the LC cells were also determined. In addition, the method is available to a wide range of polymeric substrates, including flexible ones such as poly(ethylene terephthalate).
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| 8. |
- Ahmadzadeh, Karan, et al.
(författare)
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Efficient implementation of isotropic cubic response functions for two-photon absorption cross sections within the self-consistent field approximation
- 2021
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:2
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Tidskriftsartikel (refereegranskat)abstract
- Within the self-consistent field approximation, computationally tractable expressions for the isotropic second-order hyperpolarizability have been derived and implemented for the calculation of two-photon absorption cross sections. The novel tensor average formulation presented in this work allows for the evaluation of isotropic damped cubic response functions using only similar to 3.3% (one-photon off-resonance regions) and similar to 10% (one-photon resonance regions) of the number of auxiliary Fock matrices required when explicitly calculating all the needed individual tensor components. Numerical examples of the two-photon absorption cross section in the one-photon off-resonance and resonance regions are provided for alanine-tryptophan and 2,5-dibromo-1,4-bis(2-(4-diphenylaminophenyl)vinyl)-benzene. Furthermore, a benchmark set of 22 additional small- and medium-sized organic molecules is considered. In all these calculations, a quantitative assessment is made of the reduced and approximate forms of the cubic response function in the one-photon off-resonance regions and results demonstrate a relative error of less than similar to 5% when using the reduced expression as compared to the full form of the isotropic cubic response function.
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| 9. |
- Ahmadzadeh, Karan, et al.
(författare)
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Efficient Kohn-Sham density-functional theory implementation of isotropic spectroscopic observables associated with quadratic response functions
- 2022
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Ingår i: Electronic Structure. - : IOP Publishing. - 2516-1075. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- For general exchange-correlation functionals with a dependence on the local spin densities and spin-density gradients, we provide computationally tractable expressions for the tensor-averaged quadratic response functions pertinent to the experimental observables in second-harmonic generation (SHG). We demonstrate how the tensor-averaged quantities can be implemented with reference to a derived minimal number of first- and second-order perturbed Fock matrices. Our consideration has the capability of treating a situation of resonance enhancement as it is based on damped response theory and allows for the evaluation of tensor-averaged resonant-convergent quadratic response functions using only similar to 25% (one-photon off-resonance regions) and similar to 50% (one-photon resonance regions) of the number of auxiliary Fock matrices required when explicitly calculating all the needed individual tensor components. Numerical examples of SHG intensities in the one-photon off-resonance region are provided for a sample of makaluvamine derivatives recognized for their large nonlinear optical responses as well as a benchmark set of small- and medium-sized organic molecules.
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| 10. |
- Ai, Yuejie, et al.
(författare)
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Hydrophobicity and Hydrophilicity Balance Determines Shape Selectivity of Suzuki Coupling Reactions Inside Pd@meso-SiO2 Nanoreactor
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:19, s. 10244-10251
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Tidskriftsartikel (refereegranskat)abstract
- Molecular sorting and catalysis directed by shape selectivity have been extensively applied in porous extended frameworks for a low-carbon, predictable, renewable component of modern industry. A comprehensive understanding of the underlying recognition mechanism toward different shapes is unfortunately still missing, owing to the lack of structural and dynamic information under operating conditions. We demonstrate here that such difficulties can be overcome by state-of-the-art molecular dynamics simulations which provide atomistic details that are not accessible experimentally, as exemplified by our interpretation for the experimentally observed aggregation induced shape selectivity for Suzuki C-C coupling reaction catalyzed by Pd particles in mesoporous silica. It is found that both aggregation ability and aggregating pattern of the reactants play the decisive role in controlling the shape selectivity, which are in turn determined by the balance between the hydrophobicity and hydrophilicity of the reactants, or in other words, by the balance between the noncovalent hydrogen bonding interaction and van der Waals forces. A general rule that allows prediction of the shape selectivity of a reactant has been proposed and verified against experiments. We show that molecular modeling is a powerful tool for rational design of new mesoporous systems and for the control of catalytic reactions that are important for the petrochemical industry.
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