We introduce density functional theory and review recent progress in its application to transition metal chemistry. Topics covered include local, meta, hybrid, hybrid meta, and range-separated functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including molecules, clusters, nanoparticles, surfaces, and solids.

Density functional theory for transition metals and transition metal chemistry

Designing systems with large magnetic anisotropy is critical to realize nanoscopic magnets. Thus far, the magnetic anisotropy energy per atom in single-molecule magnets and ferromagnetic films remains typically one to two orders of magnitude below the theoretical limit imposed by the atomic spin-orbit interaction. We realized the maximum magnetic anisotropy for a 3d transition metal atom by coordinating a single Co atom to the O site of an MgO(100) surface. Scanning tunneling spectroscopy reveals a record-high zero-field splitting of 58 millielectron volts as well as slow relaxation of the Co atom's magnetization. This striking behavior originates from the dominating axial ligand field at the O adsorption site, which leads to out-of-plane uniaxial anisotropy while preserving the gas-phase orbital moment of Co, as observed with x-ray magnetic circular dichroism.

http://science.sciencemag.org/content/sci/344/6187/988.full.pdf

Reaching the magnetic anisotropy limit of a 3d metal atom

A permanent magnet retains a substantial fraction of its saturation magnetization in the absence of an external magnetic field. Realizing magnetic remanence in a single atom allows for storing and processing information in the smallest unit of matter. We show that individual holmium (Ho) atoms adsorbed on ultrathin MgO(100) layers on Ag(100) exhibit magnetic remanence up to a temperature of 30 kelvin and a relaxation time of 1500 seconds at 10 kelvin. This extraordinary stability is achieved by the realization of a symmetry-protected magnetic ground state and by decoupling the Ho spin from the underlying metal by a tunnel barrier.

https://science.sciencemag.org/content/sci/352/6283/318.full.pdf

Magnetic remanence in single atoms

The increasing availability of quantum-chemical data on surface reaction intermediates invites one to revisit unresolved mechanistic issues in heterogeneous catalysis. One such issue of particular current interest is the molecular basis of the Fischer–Tropsch reaction. Here we review current molecular understanding of this reaction that converts synthesis gas into longer hydrocarbons where we especially elucidate recent progress due to the contributions of computational catalysis. This perspective highlights the theoretical approach to heterogeneous catalysis that aims for kinetic prediction from quantum-chemical first principle data. Discussion of the Fischer–Tropsch reaction from this point of view is interesting because of the several mechanistic options available for this reaction. There are many proposals on the nature of the monomeric single C atom containing intermediate that is inserted into the growing hydrocarbon chain as well as on the nature of the growing hydrocarbon chain itself. Two dominant conflicting mechanistic proposals of the Fischer–Tropsch reaction that will be especially compared are the carbide mechanism and the CO insertion mechanism, which involve cleavage of the C–O bond of CO before incorporation of a CHx species into the growing hydrocarbon chain (the carbide mechanism) or after incorporation into the growing hydrocarbon chain (the CO insertion mechanism). The choice of a particular mechanism has important kinetic consequences. Since it is based on molecular information it also affects the structure sensitivity of this particular reaction and hence influences the choice of catalyst composition. We will show how quantum-chemical information on the relative stability of relevant reaction intermediates and estimates of the rate constants of corresponding elementary surface reactions provides a firm foundation to the kinetic analysis of such reactions and allows one to discriminate between the different mechanistic options. The paper will be concluded with a short perspective section dealing with the needs for future research. Many of the current key questions on the physical chemistry as well as computational study of heterogeneous catalysis relate to particular topics for further research on the fundamental aspects of Fischer–Tropsch catalysis.

/pdf/mechanism-and-microkinetics-of-the-fischer-tropsch-reaction-2401aj4322.pdf

Mechanism and microkinetics of the Fischer–Tropsch reaction

The results of a systematic study of the interaction of small coinage metal clusters (Mn, n = 1-3) and extended deposition (one and two MLs; ML = monolayer) with the regular and locally defected (Fs center and divacancy) neutral MgO(100) surface are presented. The calculations have been performed at the DFT level employing plane waves as a basis set and using a gradient-corrected exchange-correlation functional (PW91). The adhesion energy along the group follows a trend that can be rationalized in terms of the strength and "stickiness" of the metallic bond, electrostatic polarization effects, and chemical interactions. Coinage metal dimers and trimers are absorbed on the regular surface in an upright position with little modification with respect to the gas-phase structure and can easily diffuse from site to site (in the case of trimers, also because of their fluxional character). In the case of extended deposition, the adhesion energy increases when passing from one to two MLs because of a "metal-on-top" stabilization mechanism. Neutral localized defects on the surface such as the Fs center (generated by a missing O atom) and the double vacancy (generated by a missing MgO dimer) act as strong trapping centers for small clusters and remarkably increase the adhesion of metal slabs to the surface in the case of extended deposition. At variance with the Fs center, the double vacancy induces a strong structural and energetic modification of the surrounding oxide lattice, varying also as a function of the metal deposition. A peculiar structural rearrangement consisting of the segregation of the metal slab into "islands" on the surface is observed in the case of one ML Cu and (to a lesser extent) Au.

The Interaction of Coinage Metal Clusters with the MgO(100) Surface.

Structure and bonding of complexes formed by 17 different single transition metal atoms (Cu, Ag, Au; Ni, Pd, Pt; Co, Rh, Ir; Fe, Ru, Os; Mn, Re; Cr, Mo, W) with oxygen sites of the regular MgO(001) surface were studied computationally. We employed an all-electron scalar-relativistic density functional method in combination with our novel scheme of cluster models embedded in an elastic polarizable environment that allows one to account for substrate relaxation. Even on a rigid substrate such as ideal MgO(001), adsorbate-induced relaxation noticeably affects structure and stability of surface complexes. For more reliable estimates, we calculated adsorption energies with two different gradient-corrected exchange-correlation functionals, BP86 and PBEN. More than one electron configuration was considered for metal atoms exhibiting high-spin states adsorption complexes. Within one group of the periodic table, 3d-atoms, in general, were found to adsorb more strongly than 4d-atoms, but weaker than 5d-atoms. In line with our previous studies of selected d-metal atoms adsorbed on oxides, the surface complexes considered did now show any indication of metal oxidation.

Adsorption of d-metal atoms on the regular MgO(001) surface: Density functional study of cluster models embedded in an elastic polarizable environment

A method for brightness correction of defective pixels of digital monochrome image consisting in calculation of defective pixel brightness values over its neighborhood, creation of a defective pixel map that is used to determine a defective cluster perimeter preferably quadruply-connected one and calculate brightness value of each defective pixel belonging to such a perimeter; performing such a procedure iteratively until brightness value of each defective pixel has been calculated; defective pixel brightness value is calculated as an average weighed value over neighboring pixel brightness values. The technical result of the claimed method consists in increased quality of obtained image by means of brightness correction of defective pixels of a digital monochrome image.

Method for Brightness Correction of Defective Pixels of Digital Monochrome Image

The invention relates to methods for evaluation a level of brightness in the area of interest of the digital x-ray image for medical applications by means of the image histogram using a neural network. The calculations comprise of: image acquisition, image histogram calculation, converting histogram values into input arguments of the neural network and output values of the neural network acquiring. As input arguments of the neural network the histogram values calculated with the given class interval and normalized to unit are used. The level of brightness is calculated as a linear function of the output value of the neural network. Neural network learning is performed using a learning set calculated on the base of the given image database; as a set of target values the levels of brightness calculated for each image over the area of interest and scaled to the range of the activation function of a neuron in the output layer of the neural network are used.

Method for brightness level calculation in the area of interest of a digital x-ray image for medical applications

The invention relates to the method for measuring of geometrical shift in flat panel x-ray image sensors using a test device. A test device comprising at least two edge test devices is placed on the detector's operating surface, The test device is exposed to x-rays in order to get its x-ray image where ROIs having pixels coordinates corresponding to the edge of each test device are identified. The pixel coordinates are used to determine sensor geometrical shifts considering minimum value of an objective function. Technical result involves expansion of technical means of definite application and a possibility to measure sensor geometrical shift with sufficient accuracy

Method for determination of geometrical sensor shifts in flat panel x-ray image detectors

FIELD: physics ^ SUBSTANCE: image is taken, its histogram is calculated, values of the histogram are converted to input arguments of a neural network and the output value of the neural network is calculated The input arguments of the neural network used are normalised to the unit value of the histogram calculated with a given class interval The brightness level is calculated as a linear function of the output value of the neural network The neural network is trained using a learning set calculated on a given image base The set of target values used is the brightness levels calculated for each image on the area of interest and scaled to the range of the neuron activation function of the output layer of the neural network ^ EFFECT: high rate of processing a digital image ^ 6 cl, 5 dwg

Ruslan Nikolaevich Kosarev

Papers

Adsorption of d-metal atoms on the regular MgO(001) surface: Density functional study of cluster models embedded in an elastic polarizable environment

Method for Brightness Correction of Defective Pixels of Digital Monochrome Image

Method for brightness level calculation in the area of interest of a digital x-ray image for medical applications

Method for determination of geometrical sensor shifts in flat panel x-ray image detectors

Method of determining brightness level in area of interest on digital medical x-ray picture