Search results for "Density Functional Theory"
showing 10 items of 981 documents
Pressure-induced chemical decomposition of copper orthovanadate (α-Cu3V2O8)
2021
The high pressure stability of α-Cu3V2O8 has been investigated via complementary high pressure synchrotron X-ray diffraction experiments and theoretical density functional theory calculations. The results of both experiment and theory are in close agreement. The main result of this work is that α-Cu3V2O8 undergoes a pressure-induced chemical decomposition into CuO and V2O5 at a modest pressure of ∼1.35 GPa according to the experimental observations, and at ∼2.45 GPa according to the calculations. The decomposition is investigated with enthalpy calculations and one of the main driving factors is the stability of the octhedral oxygen-coordination of the metal atoms in the decompositon product…
Characterization of theTiSiO4structure and its pressure-induced phase transformations: Density functional theory study
2009
Theoretical investigations concerning the possible titanium silicate polymorphs have been performed using density functional theory at B3LYP level. Total-energy calculations and geometry optimizations have been carried out for all phases involved. The following sequence of pressure-driven structural transitions has been found: ${\text{CrVO}}_{4}$-type, $Cmcm$ (in parenthesis the transition pressure), $\ensuremath{\rightarrow}$ zircon-type, $I{4}_{1}/amd$ (0.8 GPa), $\ensuremath{\rightarrow}$ scheelite-type, $I{4}_{1}/a$ (3.8 GPa). At higher pressure the last phase is found to be stable at least up to 25 GPa. The equation of state of the different polymorphs is also reported. We found that t…
Evidence of a sudden increase in the nuclear size of proton-rich silver-96
2021
Understanding the evolution of the nuclear charge radius is one of the long-standing challenges for nuclear theory. Recently, density functional theory calculations utilizing Fayans functionals have successfully reproduced the charge radii of a variety of exotic isotopes. However, difficulties in the isotope production have hindered testing these models in the immediate region of the nuclear chart below the heaviest self-conjugate doubly-magic nucleus 100Sn, where the near-equal number of protons (Z) and neutrons (N) lead to enhanced neutron-proton pairing. Here, we present an optical excursion into this region by crossing the N = 50 magic neutron number in the silver isotopic chain with th…
Modeling red coral (Corallium rubrum) and African snail (Helixia aspersa) shell pigments: Raman spectroscopyversusDFT studies
2016
Pigments from red coral (Corallium rubrum) and African snail (Helixia aspersa) shell were studied non-invasively using Raman spectroscopy with 1064-nm laser beam. The two observed bands because of organic pigments confined in biomineralized CaCO3 matrix at about 1500 and 1100 cm−1 were assigned to ν(CC) and ν(C―C), respectively. Both signals originate from polyene(s) of largely unknown structure, containing several conjugated CC bonds. The small peak at 1016 cm−1 in the Raman spectrum of coral pigment was assigned to in-plane ―CH3 rocking or structural deformation of polyene chain because of spatial confinement in the mineral matrix. The organic pigments in red coral and snail shell were pr…
Cavitation of electron bubbles in liquid parahydrogen
2011
Within a finite-temperature density functional approach, we have investigated the structure of electron bubbles in liquid parahydrogen below the saturated vapour pressure, determining the critical pressure at which electron bubbles explode as a function of temperature. The electron-parahydrogen interaction has been modelled by a Hartree-type local potential fitted to the experimental value of the conduction band-edge for a delocalized electron in pH(2). We have found that the pressure for bubble explosion is, in absolute value, about a factor of two smaller than that of the homogeneous cavitation pressure in the liquid. Comparison with the results obtained within the capillary model shows t…
Isotropic-nematic interface in suspensions of hard rods: Mean-field properties and capillary waves
2006
We present a study of the isotropic-nematic interface in a system of hard spherocylinders. First we compare results from Monte Carlo simulations and Onsager density functional theory for the interfacial profiles of the orientational order parameter and the density. Those interfacial properties that are not affected by capillary waves are in good agreement, despite the fact that Onsager theory overestimates the coexistence densities. Then we show results of a Monte Carlo study of the capillary waves of the interface. In agreement with recent theoretical investigations (Eur.Phys.J. E {\bf 18} 407 (2005)) we find a strongly anistropic capillary wave spectrum. For the wave-numbers accessed in o…
Halogen effect on structure and 13 C NMR chemical shift of 3,6-disubstituted-N -alkyl carbazoles
2013
Structures of selected 3,6-dihalogeno-N-alkyl carbazole derivatives were calculated at the B3LYP/6-311++G(3df,2pd) level of theory, and their 13C nuclear magnetic resonance (NMR) isotropic shieldings were predicted using density functional theory (DFT). The model compounds contained 9H, N-methyl and N-ethyl derivatives. The relativistic effect of Br and I atoms on nuclear shieldings was modeled using the spin–orbit zeroth-order regular approximation (ZORA) method. Significant heavy atom shielding effects for the carbon atom directly bonded with Br and I were observed (~−10 and ~−30 ppm while the other carbon shifts were practically unaffected). The decreasing electronegativity of the haloge…
8-Hydroxyquinoline-2-Carboxylic Acid as Possible Molybdophore: A Multi-Technique Approach to Define Its Chemical Speciation, Coordination and Sequest…
2020
8-hydroxyquinoline-2-carboxylic acid (8-HQA) has been found in high concentrations (0.5&ndash
New fitting scheme to obtain effective potential from Car-Parrinello molecular dynamics simulations: Application to silica
2008
A fitting scheme is proposed to obtain effective potentials from Car-Parrinello molecular dynamics (CPMD) simulations. It is used to parameterize a new pair potential for silica. MD simulations with this new potential are done to determine structural and dynamic properties and to compare these properties to those obtained from CPMD and a MD simulation using the so-called BKS potential. The new potential reproduces accurately the liquid structure generated by the CPMD trajectories, the experimental activation energies for the self-diffusion constants and the experimental density of amorphous silica. Also lattice parameters and elastic constants of alpha-quartz are well-reproduced, showing th…
Simulations of a Graphene Nanoflake as a Nanovector To Improve ZnPc Phototherapy Toxicity: From Vacuum to Cell Membrane
2017
International audience; We propose a new approach to improving photodynamic therapy (PDT) by transporting zinc phthalocyanine (ZnPc) in biological systems via a graphene nanoflake, to increase its targeting. Indeed, by means of time-dependent density functional theory simulations, we show that the ZnPc molecule in interaction with a graphene nanoflake preserves its optical properties not only in a vacuum but also in water. Moreover, molecular dynamic simulations demonstrate that the graphene nanoflake/ZnPc association, as a carrier, permits one to stabilize the ZnPc/graphene nanoflake system on the cellular membrane, which was not possible when using ZnPc alone. We finally conclude that the…