The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Rustam Z Khaliullin - One of the best experts on this subject based on the ideXlab platform.
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direct unconstrained variable metric localization of one Electron Orbitals
Journal of Chemical Theory and Computation, 2020Co-Authors: Rustam Z KhaliullinAbstract:Spatially localized one-Electron Orbitals, orthogonal and non-orthogonal, are widely used in Electronic structure theory to describe chemical bonding and speed up calculations. In order to avoid li...
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direct unconstrained variable metric localization of one Electron Orbitals
arXiv: Chemical Physics, 2020Co-Authors: Rustam Z KhaliullinAbstract:Spatially localized one-Electron Orbitals, orthogonal and nonorthogonal, are widely used in Electronic structure theory to describe chemical bonding and speed up calculations. In order to avoid linear dependencies of localized Orbitals, the existing localization methods either constrain orbital transformations to be unitary, that is, metric preserving, or, in the case of variable-metric methods, fix the centers of nonorthogonal localized Orbitals. Here, we developed a different approach to orbital localization, in which these constraints are replaced with a single restriction that specifies the maximum allowed deviation from the orthogonality for the final set of localized Orbitals. This reformulation, which can be viewed as a generalization of existing localization methods, enables one to choose the desired balance between the orthogonality and locality of the Orbitals. Furthermore, the approach is conceptually and practically simple as it obviates the necessity in unitary transformations and allows to determine optimal positions of the centers of nonorthogonal Orbitals in a unconstrained and straightforward minimization procedure. It is demonstrated to produce well-localized orthogonal and nonorthogonal Orbitals with the Berghold and Pipek-Mezey localization functions for a variety of molecules and periodic materials including large systems with non-trivial bonding.
Paolo Giannozzi - One of the best experts on this subject based on the ideXlab platform.
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reconstruction of frozen core all Electron Orbitals from pseudo Orbitals
Journal of Chemical Physics, 2001Co-Authors: Balazs Hetenyi, Filippo De Angelis, Paolo GiannozziAbstract:We investigate the numerical feasibility of reconstructing frozen-core all-Electron molecular Orbitals from corresponding pseudo-Orbitals. We perform density-functional calculations on simple atomic and molecular model systems using ultrasoft pseudopotentials to represent the atomic cores. We apply a transformation due to Blochl [Phys. Rev. B 50, 17953 (1994)] to each calculated pseudo-orbital to obtain a corresponding frozen-core all-Electron molecular orbital. Our model systems include the reconstruction of the 5d orbital of a gold atom, and the occupied valence states of the TiO2 molecule. Comparison of the resulting all-Electron Orbitals to corresponding ones that were obtained from calculations in which the core Electrons were explicitly included indicates that all-Electron molecular orbital reconstruction is a feasible and useful operation in reproducing the correct behavior of molecular Orbitals in the nuclear core regions.
Andre K Mkhoyan - One of the best experts on this subject based on the ideXlab platform.
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probing core Electron Orbitals by scanning transmission Electron microscopy and measuring the delocalization of core level excitations
Physical Review B, 2016Co-Authors: Jong Seok Jeong, Michael L Odlyzko, Peng Xu, Bharat Jalan, Andre K MkhoyanAbstract:By recording low-noise energy-dispersive x-ray spectroscopy maps from crystalline specimens using aberration-corrected scanning transmission Electron microscopy, it is possible to probe core-level Electron Orbitals in real space. Both the 1s and 2p Orbitals of Sr and Ti atoms in SrTiO3 are probed, and their projected excitation potentials are determined. This paper also demonstrates experimental measurement of the Electronic excitation impact parameter and the delocalization of an excitation due to Coulombic beam-orbital interaction.
Balazs Hetenyi - One of the best experts on this subject based on the ideXlab platform.
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reconstruction of frozen core all Electron Orbitals from pseudo Orbitals
Journal of Chemical Physics, 2001Co-Authors: Balazs Hetenyi, Filippo De Angelis, Paolo GiannozziAbstract:We investigate the numerical feasibility of reconstructing frozen-core all-Electron molecular Orbitals from corresponding pseudo-Orbitals. We perform density-functional calculations on simple atomic and molecular model systems using ultrasoft pseudopotentials to represent the atomic cores. We apply a transformation due to Blochl [Phys. Rev. B 50, 17953 (1994)] to each calculated pseudo-orbital to obtain a corresponding frozen-core all-Electron molecular orbital. Our model systems include the reconstruction of the 5d orbital of a gold atom, and the occupied valence states of the TiO2 molecule. Comparison of the resulting all-Electron Orbitals to corresponding ones that were obtained from calculations in which the core Electrons were explicitly included indicates that all-Electron molecular orbital reconstruction is a feasible and useful operation in reproducing the correct behavior of molecular Orbitals in the nuclear core regions.
A N Chaika - One of the best experts on this subject based on the ideXlab platform.
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visualization of Electron Orbitals in scanning tunneling microscopy
Jetp Letters, 2014Co-Authors: A N ChaikaAbstract:Scanning tunneling microscopy (STM) is one of the main techniques for direct visualization of the surface Electronic structure and chemical analysis of multi-component surfaces at the atomic scale. This review is focused on the role of the tip orbital structure and tip-surface interaction in STM imaging with picometer spatial resolution. Fabrication of STM probes with well-defined structure and selective visualization of individual Electron Orbitals in the STM experiments with controlled tunneling gap and probe structure are demonstrated.
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Application of single crystalline tungsten for fabrication of high resolution STM probes with controlled structure
Russian Metallurgy (Metally), 2011Co-Authors: A N Chaika, S. S. Nazin, V. N. Semenov, V. G. Glebovskiy, S. I. Bozhko, O. Lübben, S. A. Krasnikov, K. Radican, I. V. ShvetsAbstract:The possibility to fabricate scanning tunneling microscopy (STM) probes with controlled Electronic structure using single crystalline tungsten tips is discussed. High resolution power of oriented single crystalline probes is demonstrated in atomic and subatomic resolution STM studies of silicon, gallium telluride and graphite surfaces. The possibility of controllable selection of the tungsten tip atom Electron Orbitals responsible for the surface imaging in STM experiments is demonstrated.
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Selecting the tip Electron orbital for scanning tunneling microscopy imaging with sub-ångström lateral resolution
EPL, 2010Co-Authors: A N Chaika, S. S. Nazin, V. N. Semenov, S. I. Bozhko, O. Lübben, S. A. Krasnikov, K. Radican, I. V. ShvetsAbstract:We report on scanning tunneling microscopy (STM) studies performed with single crystalline W[001] tips on a graphite(0001) surface. Results of distance-dependent STM experiments with sub-angstrom lateral resolution and density functional theory Electronic structure calculations show how to controllably select one of the tip Electron Orbitals for high-resolution STM imaging. This is confirmed by experimental images reproducing the shape of the 5dxz, yz and 5dx2−y2 tungsten atomic Orbitals. The presented data demonstrate that the application of oriented single crystalline probes can provide further control of spatial resolution and expand the capabilities of STM.