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density functional theory

Yogesh Gawale, Nagaiyan Sekar
Density Functional Theory and Time Dependent Density Functional Theory computations reveal experimental trends accurately and provide an insight into the origin of red shifted optical spectra, large Stokes shift, nonlinear optical responses and quantitative description of the singlet-triplet energy gap of recently synthesized highly fluorescent membrane permeable benz[c,d]indole N-heteroarene BF2 rigidified BBN and BBC dyes. Our results benchmark the importance of the DFT functionals and polarization functions using the accurate basis set for the calculations of excitation energies, band gaps, dipole moment, non-linear optical properties and geometrical parameters...
December 7, 2017: Journal of Photochemistry and Photobiology. B, Biology
Juan Sanz García, Federica Maschietto, Marco Campetella, Ilaria Ciofini
To provide tools to interpret photochemical reactions, in this paper we demonstrate how a recently developed density-based index (DCT), up to now used in conjunction with Time Dependent Density Functional Theory methods, can be extended to multi-configurational methods. This index can guide chemists in the interpretation of photochemical reactions providing a measure of the spatial extent of a photo-induced charge transfer and, more generally, of charge transfer phenomena. This qualitative and quantitative description can be particularly relevant in the case of multi-configurational calculations providing a simple tool for the interpretation of their complex outputs...
December 12, 2017: Journal of Physical Chemistry. A
Shane M Parker, Dmitrij Rappoport, Filipp Furche
We report on the efficient Turbomole implementation of quadratic response properties within the time-dependent density functional theory (TDDFT) context that includes the static and dynamic dipole hyperpolarizability, ground-to-excited-state two-photon absorption amplitudes (through a single residue) and state-to-state one-photon absorption amplitudes (through a double residue). Our implementation makes full use of arbitrary (including non-Abelian) point-group symmetry as well as permutational symmetry and enables the calculation of nonlinear properties with hybrid density functionals for molecules with hundreds of atoms and thousands of basis functions at a cost that is a fixed multiple of the cost of the corresponding linear properties...
December 12, 2017: Journal of Chemical Theory and Computation
Jinlian Lu, Wei Luo, Junsheng Feng, Hongjun Xiang
Two-dimensional (2D) ferroelectricity have attracted much attention due to their applications in novel miniaturized devices such as non-volatile memories, field effect transistors and sensors. Since most of the commercial ferroelectric (FE) devices are based on ABO3 perovskite oxides, it is important to investigate the properties of 2D ferroelectricity in perovskite oxides thin films. Here, based on density functional theory (DFT) calculations, we find that there exist three kinds of in-plane ferroelectric states which originate from different microscopic mechanisms: (i) a proper FE state with the polarization along [110] due to the second-order Jahn-Teller effect related to the B ion with empty d-orbitals; (ii) a robust FE state with the polarization along [100] induced by the surface effect; (iii) a hybrid improper FE state with the polarization along [110] that is induced by the tri-linear coupling between two rotational modes and the A-site displacement...
December 12, 2017: Nano Letters
Luca Bertini, Raffaella Breglia, Matteo Lambrughi, Piercarlo Fantucci, Luca De Gioia, Marco Borsari, Marco Sola, Carlo Augusto Bortolotti, Maurizio Bruschi
Lytic polysaccharide monooxygenases (LPMOs) are Cu-containing enzymes that facilitate the degradation of recalcitrant polysaccharides by the oxidative cleavage of glycosidic bonds. They are gaining rapidly increasing attention as key players in biomass conversion, especially for the production of second-generation biofuels. Elucidation of the detailed mechanism of the LPMO reaction is a major step toward the assessment and optimization of LPMO efficacy in industrial biotechnology, paving the way to utilization of sustainable fuel sources...
December 12, 2017: Inorganic Chemistry
Hongbo Qin, Xinghe Luan, Chuang Feng, Daoguo Yang, Guoqi Zhang
For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson's ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness...
December 12, 2017: Materials
Raffaella Demichelis, Natalya A Garcia, Paolo Raiteri, Riccardo Innocenti Malini, Colin L Freeman, John H Harding, Julian D Gale
A new force field has been derived for the aqueous calcium phosphate system that aims to reproduce the key thermodynamic properties of the system, including free energies of hydration of the ions and the solubility of the solid mineral phases. Interactions of three phosphate anions (PO 3-, HPO 2- and H PO -) with water were calibrated through comparison with the results 4424 obtained from ab initio molecular dynamics using both GGA and hybrid density functional theory with dispersion corrections. In the solid state, the force field has been evaluated by benchmarking against experiment and other existing models and is shown to reproduce the structural and mechanical properties well, despite the primary focus being on thermodynamics...
December 12, 2017: Journal of Physical Chemistry. B
Peter J Diemer, Jacori Hayes, Evan Welchman, Rawad Hallani, Sujitra J Pookpanratana, Christina A Hacker, Curt A Richter, John E Anthony, Timo Thonhauser, Oana D Jurchescu
Organic field-effect transistor (OFET) performance is dictated by its composition and geometry, as well as the quality of the organic semiconductor (OSC) film, which strongly depends on purity and microstructure. When present, impurities and defects give rise to trap states in the bandgap of the OSC, lowering device performance. Here, 2,8-difluoro-5,11-bis(triethylsilylethynyl)-anthradithiophene is used as a model system to study the mechanism responsible for performance degradation in OFETs due to isomer coexistence...
January 2017: Advanced Functional Materials
Damir Borovac, Chee-Keong Tan, Nelson Tansu
We present a Density Functional Theory (DFT) analysis of the optical properties of dilute-As GaN1-xAsx alloys with arsenic (As) content ranging from 0% up to 12.5%. The real and imaginary parts of the dielectric function are investigated, and the results are compared to experimental and theoretical values for GaN. The analysis extends to present the complex refractive index and the normal-incidence reflectivity. The refractive index difference between GaN and GaNAs alloys can be engineered to be up to ~0.35 in the visible regime by inserting relatively low amounts of As-content into the GaN system...
December 11, 2017: Scientific Reports
Maria Montagna, Olga Guskova
In this computational work we investigate the photosensitive cationic surfactants with the trimethylammonium or polyamine hydrophilic head and the azobenzene-containing hydrophobic tail. The azobenzene-based molecules are known to undergo a reversible trans-cis-trans isomerization reaction when subjected to UV-Visible light irradiation. Combining the density functional theory and the all-atom molecular dynamics simulations, the structural, optical and the hydration properties of the trans- and the cis-isomers and their interaction with the oppositely charged poly(methacrylic acid) in aqueous solution are investigated...
December 11, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Pedro Borlido, Miguel A L Marques, Silvana Botti
Hybrid functionals are by now the state-of-the-art for the calculation of electronic properties of solids within density functional theory. The key to their performance is how a part of Fock exchange is mixed with a semi-local exchange-correlation functional. The choice of the mixing parameter is particularly critical in non-homogeneous systems, such as an interface between two solid phases. In this work we propose a local mixing function that is a functional of the electron density through an estimator of the local dielectric function...
December 11, 2017: Journal of Chemical Theory and Computation
Aimin Ge, Benjamin Rudshteyn, Jingyi Zhu, Reinhard J Maurer, Victor S Batista, Tianquan Lian
A combination of time-resolved vibrational spectroscopy and density functional theory techniques have been applied to study the vibrational energy relaxation dynamics of the Re(4,4'-dicyano-2,2'-bipyridine)(CO)3Cl (Re(CO)3Cl) catalyst for CO2 to CO conversion bound to gold surfaces. The kinetics of vibrational relaxation exhibits a biexponential decay including an ultrafast initial relaxation and complete recovery of the ground vibrational state. Ab initio molecular dynamics simulations and time-dependent perturbation theory reveal the former to be due to vibrational population exchange between CO stretching modes and the latter to be a combination of intramolecular vibrational relaxation (IVR) and electron-hole pair (EHP) induced energy transfer into the gold substrate...
December 11, 2017: Journal of Physical Chemistry Letters
Trenton Tovar, Ivan Iordanov, Dorina Sava Gallis, Jared Bernard DeCoste
For small, nonpolar adsorbates, physisorption is dominated by weak Van der Waals interactions limiting the adsorption capacity. A common strategy to enhance the adsorption properties of isoreticular metal-organic framework (MOFs), such as UiO-66, is to add functional groups to the organic linker. Low and high pressure O2 isotherms were measured on UiO-66 MOFs functionalized with electron donating and withdrawing groups. It was found that the electron donating effects of -NH2, -OH, and -OCF3 groups enhance the uptake of O2...
December 11, 2017: Chemistry: a European Journal
Reed Nieman, Hsinhan Tsai, Wanyi Nie, Adelia J A Aquino, Aditya D Mohite, Sergei Tretiak, Hao Li, Hans Lischka
Organic photovoltaic donor-acceptor junction devices composed of π-conjugated polymer electron donors (D) and fullerene electron acceptors (A) show greatly increased performance when a spacer material is inserted between the two layers (W. Y. Nie, G. Gupta, B. K. Crone, F. L. Liu, D. L. Smith, P. P. Ruden, C. Y. Kuo, H. Tsai, H. L. Wang, H. Li, S. Tretiak and A. D. Mohite, Adv. Sci., 2015, 2, 1500024.). For instance, experimental results reveal significant improvement of photocurrent when a terthiophene oligomer derivative is inserted in between π-conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) donor and C60 acceptor...
December 11, 2017: Nanoscale
Camilla Abbehausen, Raphael Enoque Ferraz de Paiva, Ragnar Bjornsson, Saulo Quintana Gomes, Zhifeng Du, Pedro Paulo Corbi, Frederico Alves Lima, Nicholas Farrell
A combination of two elements' (Au, Zn) X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TD-DFT) allowed the elucidation of differential substitution pathways of Au(I) and Au(III) compounds reacting with biologically relevant zinc fingers (ZnFs). Gold L3-edge XAS probed the interaction of gold and the C-terminal Cys2HisCys finger of the HIV-1 nucleocapsid protein NCp7, and the Cys2His2 human transcription factor Sp1. The use of model compounds helped assign oxidation states and the identity of the gold-bound ligands...
December 11, 2017: Inorganic Chemistry
Daniel Plaul, Michael Böhme, Serghei Ostrovsky, Zbigniew Tomkowicz, Helmar Görls, Wolfgang Haase, Winfried Plass
The new tritopic triaminoguanidine-based ligand 1,2,3-tris[(pyridine-2-ylmethylidene)amino]guanidine (H2pytag) was synthesized. The reaction of a mixture of cobalt(II) chloride and cobalt(II) perchlorate with the ligand H2pytag in pyridine solution leads to the formation of the trinuclear cobalt(II) complex [Co3(pytag)(py)6Cl3]ClO4. Three octahedrally coordinated high-spin cobalt(II) ions are linked through the bridging triaminoguanidine backbone of the ligand leading to an almost equilateral triangular arrangement...
December 11, 2017: Inorganic Chemistry
Dongyue Liang, Jiewei Hong, Dong Fang, Joseph W Bennett, Sara E Mason, Robert J Hamers, Qiang Cui
We describe a strategy of integrating quantum mechanical (QM), hybrid quantum mechanical/molecular mechanical (QM/MM) and MM simulations to analyze the physical properties of a solid/water interface. This protocol involves using a correlated ab initio (CCSD(T)) method to first calibrate Density Functional Theory (DFT) as the QM approach, which is then used in QM/MM simulations to compute relevant free energy quantities at the solid/water interface using a mean-field approximation of Yang et al. that decouples QM and MM thermal fluctuations; gas-phase QM/MM and periodic DFT calculations are used to determine the proper QM size in the QM/MM simulations...
December 11, 2017: Physical Chemistry Chemical Physics: PCCP
J Qiu, B Song, X Li, A F Cozzolino
The solution and gas phase halide binding to a bis-antimony(iii) anion receptor was studied. This new class of anion receptors utilizes the strong Sb-centered secondary bonding interactions (SBIs) that are formed opposite to the polar Sb-O primary bond. 1H NMR titration data were fitted statistically to binding models and solution-phase binding energetics were extracted, while the formation of anion-to-receptor complexes was observed using ESI-MS. Density functional theory calculations suggest that their affinity towards binding halide anions is mitigated by the strong explicit solvation effect in DMSO, which gives insights into future designs that circumvent direct solvent binding and are anticipated to yield tighter and perhaps more selectivity in anion binding...
December 11, 2017: Physical Chemistry Chemical Physics: PCCP
Claire Louise Hobday, Thomas D Bennett, David Fairen-Jimenez, Alexander Graham, Carole A Morrison, David R Allan, Tina Düren, Stephen A Moggach
Many zeolitic imidazolate frameworks (ZIFs) are promising candidates for use in separation technologies. Comprising large cavities interconnected by small windows they can be used, at least in principle, as molecular sieves where molecules smaller than the window size are able to diffuse into the material while larger are rejected. However, "swing effect" or "gate opening" phenomena resulting in an enlargement of the windows have proven to be detrimental. Here, we present the first systematic experimental and computational study of the effect of chemical functionalisation of the imidazole linker on the framework dynamics...
December 11, 2017: Journal of the American Chemical Society
Ke Chen, Anupam Roy, Amritesh Rai, Amithraj Valsaraj, Xianghai Meng, Feng He, Xiaochuan Xu, Leonard Frank Register, Sanjay K Banerjee, Yaguo Wang
Understanding defect effect on carrier dynamics is essential for both fundamental physics and potential applications of transition metal dichalcogenides. Here, the phenomenon of oxygen impurities trapping photo-excited carriers has been studied with ultrafast pump-probe spectroscopy. Oxygen impurities are intentionally created in exfoliated multilayer MoSe2 with Ar+ plasma irradiation and air exposure. After plasma treatment, the signal of transient absorption first increases and then decreases, which is a signature of defect capturing carriers...
December 11, 2017: ACS Applied Materials & Interfaces
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