I describe the design, implementation, and usage of galpy, a python package for galactic-dynamics calculations. At its core, galpy consists of a general framework for representing galactic potentials ...both in python and in C (for accelerated computations); galpy functions, objects, and methods can generally take arbitrary combinations of these as arguments. Numerical orbit integration is supported with a variety of Runge-Kutta-type and symplectic integrators. For planar orbits, integration of the phase-space volume is also possible. galpy supports the calculation of action-angle coordinates and orbital frequencies for a given phase-space point for general spherical potentials, using state-of-the-art numerical approximations for axisymmetric potentials, and making use of a recent general approximation for any static potential. A number of different distribution functions (DFs) are also included in the current release; currently, these consist of two-dimensional axisymmetric and non-axisymmetric disk DFs, a three-dimensional disk DF, and a DF framework for tidal streams. I provide several examples to illustrate the use of the code. I present a simple model for the Milky Way's gravitational potential consistent with the latest observations. I also numerically calculate the Oort functions for different tracer populations of stars and compare them to a new analytical approximation. Additionally, I characterize the response of a kinematically warm disk to an elliptical m = 2 perturbation in detail. Overall, galpy consists of about 54,000 lines, including 23,000 lines of code in the module, 11,000 lines of test code, and about 20,000 lines of documentation. The test suite covers 99.6% of the code. galpy is available at http://github.com/jobovy/galpy with extensive documentation available at http://galpy.readthedocs.org/en/latest.
Combined density functional and ab initio calculations are performed on two isomorphous tetranuclear {Ni3IIILnIII} star‐type complexes Ln=Gd (1), Dy (2) to shed light on the mechanism of magnetic ...exchange in 1 and the origin of the slow magnetization relaxation in complex 2. DFT calculations correctly reproduce the sign and magnitude of the J values compared to the experiments for complex 1. Acute ∢NiOGd bond angles present in 1 instigate a significant interaction between the 4fxyz orbital of the GdIII ion and 3d${{_{x{^{2}}- y{^{2}}}$ orbital of the NiII ions, leading to rare and strong antiferromagnetic Ni⋅⋅⋅Gd interactions. Calculations reveal the presence of a strong next‐nearest‐neighbour Ni⋅⋅⋅Ni antiferromagnetic interaction in complex 1 leading to spin frustration behavior. CASSCF+RASSI‐SO calculations performed on complex 2 suggest that the octahedral environment around the DyIII ion is neither strong enough to stabilize the mJ |±15/2〉 as the ground state nor able to achieve a large ground‐state–first‐excited‐state gap. The ground‐state Kramers doublet for the DyIII ion is found to be the mJ |±13/2〉 state with a significant transverse anisotropy, leading to very strong quantum tunneling of magnetization (QTM). Using the POLY_ANISO program, we have extracted the JNiDy interaction as −1.45 cm−1. The strong Ni⋅⋅⋅Dy and next‐nearest‐neighbour Ni⋅⋅⋅Ni interactions are found to quench the QTM to a certain extent, resulting in zero‐field SMM behavior for complex 2. The absence of any ac signals at zero field for the structurally similar Dy(AlMe4)3 highlights the importance of both the Ni⋅⋅⋅Dy and the Ni⋅⋅⋅Ni interactions in the magnetization relaxation of complex 2. To the best of our knowledge, this is the first time that the roles of both the Ni⋅⋅⋅Dy and Ni⋅⋅⋅Ni interactions in magnetization relaxation of a {3d–4f} molecular magnet have been established.
Quantum tunneling: DFT and ab initio calculations suggest that both Ni⋅⋅⋅Dy and 1, 3 Ni⋅⋅⋅Ni (see figure) interactions help to quench the QTM behavior in {3d–4f} single‐molecule magnets.
Ab initio many-body perturbation theory within the GW approximation is a Green’s function formalism widely used in the calculation of quasiparticle excitation energies of solids. In what has become ...an increasingly standard approach, Kohn–Sham eigenenergies, generated from a DFT calculation with a strategically-chosen exchange–correlation functional “starting point”, are used to construct G and W, and then perturbatively corrected by the resultant GW self-energy. In practice, there are several ways to construct the GW self-energy, and these can lead to variations in predicted quasiparticle energies. For example, for ZnO and TiO2, the GW fundamental gaps reported in the literature can vary by more than 1 eV depending on the GW code used. In this work, we calculate and analyze GW quasiparticle (QP) energies of these and other systems with three different GW codes: BerkeleyGW, Abinit and Yambo. Through a systematic analysis of the GW implementation of these three codes, we identify the primary origin of major discrepancies between codes reported in prior literature to be the different implementations the Coulomb divergence in the Fock exchange term and the frequency integration scheme of the GW self-energy. We then eliminate these discrepancies by using common numerical methods and algorithms, demonstrating that the same quasiparticle energies for a given material can be obtained with different codes, within numerical differences ascribable to the technical details of the underling implementations. This work will be important for users and developers in assessing the precision of future GW applications and methods.
We present a theoretical investigation of the structural, electronic and optical properties of few layer graphene/TiO2 composites involving either single or bilayer graphene and the (101) surface of ...TiO2 anatase, in view of the importance of carbonaceous materials such as graphene to enhance solar light-driven photocatalytic activity of TiO2. Calculations have been performed by combining periodic DFT calculations to TD-DFT carried out on finite clusters extracted from the periodic structures and embedded in an array of point charges devised to reproduce the periodic electrostatic environment. Although van der Waals interactions dominate the graphene/TiO2 interaction, TiO2 properties are significantly affected by its combination with graphene in the composite materials. In particular, we found that such materials present favorable key features for photocatalysis applications, with high charge carriers mobilities, an increase of the absorption in the visible range together with a red-shift of the photoresponse of TiO2. These results confirm that graphene can enhance solar light-driven photocatalytic activity of TiO2, especially when few layer graphene-based composites are considered. Furthermore, the proposed computational approach appears as a reliable and effective tool to model both the electronic and the optical properties of heterostructures at low computational cost.
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•A reliable and effective computational protocol is proposed to model composites.•Gr-based composites offer better properties than TiO2 for photocatalysis.•Few layer Gr-based composites offer better properties than single layer ones.
ABSTRACT We present reduced data and data products from the 3D-HST survey, a 248-orbit HST Treasury program. The survey obtained WFC3 G141 grism spectroscopy in four of the five CANDELS fields: ...AEGIS, COSMOS, GOODS-S, and UDS, along with WFC3 H140 imaging, parallel ACS G800L spectroscopy, and parallel I814 imaging. In a previous paper, we presented photometric catalogs in these four fields and in GOODS-N, the fifth CANDELS field. Here we describe and present the WFC3 G141 spectroscopic data, again augmented with data from GO-1600 in GOODS-N (PI: B. Weiner). We developed software to automatically and optimally extract interlaced two-dimensional (2D) and one-dimensional (1D) spectra for all objects in the Skelton et al. (2014) photometric catalogs. The 2D spectra and the multi-band photometry were fit simultaneously to determine redshifts and emission line strengths, taking the morphology of the galaxies explicitly into account. The resulting catalog has redshifts and line strengths (where available) for 22,548 unique objects down to (79,609 unique objects down to ). Of these, 5459 galaxies are at and 9621 are at , where H falls in the G141 wavelength coverage. The typical redshift error for galaxies is , i.e., one native WFC3 pixel. The limit for emission line fluxes of point sources is erg s−1 cm−2. All 2D and 1D spectra, as well as redshifts, line fluxes, and other derived parameters, are publicly available.18
Pterins can be considered as biological jacks‐of‐all‐trades. Firstly identified as pigments in butterfly wings, they are nowadays well‐known cofactors in the synthesis of NO, nucleotides, and amino ...acids, markers in cell‐mediated immune responses. Yet, not all of their properties are beneficial. Some of these pterins contribute to the photochemical evolution of vitiligo, a depigmentation disorder. Enhanced oxidative stress and cytotoxicity lead to melanocyte destruction and tissue damage. More information can be found in the Research Article by E. M. Arpa and I. Corral (DOI: 10.1002/chem.202300519).
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