Use of one‐electron theory for the interpretation of near edge structure in K‐shell x‐ray absorption spectra of transition metal complexes
TL;DR: In this paper, the authors reported the results of multiple scattered wave SCF X-alpha calculations of the one-electron cross section for K-shell photoabsorption in the molecular complexes MoO4−−, CrO4+−, and MoS4−+−.
Abstract: We report the results of multiple scattered wave SCF X‐alpha calculations of the one‐electron cross section for K‐shell photoabsorption in the molecular complexes MoO4−−, CrO4−−, and MoS4−−. We show that the method can successfully account for energy separations and relative cross sections of spectral features both below and above the K‐shell ionization threshold. Furthermore, we show: (a) that the first fairly intense peak on the low energy side of the rising edge for molybdate and chromate is due to a dipole allowed transition to a bound antibonding state of mainly nd character on the metal ion; this transition is possible because of the mixing with the ligand p orbitals having the proper T2 symmetry induced by the tetrahedral molecular potential; (b) the shoulder on the rising absorption edge can be explained by the beginning of the steplike continuum absorption when convolved with a Lorentzian function of frequency to imitate lifetime and monochromator broadening: (c) the main absorption peak is due t...
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TL;DR: In this article, an overview of the X-ray absorption spectra of 3D transition metals and their compounds is presented, focusing on the description of the absorption process and the various routes to interpret the results within the framework of their electronic structure.
528 citations
TL;DR: Reduction from SeO4 to SeO3 appears to be a rate-limiting step in the production of volatile Se compounds by plants, and inhibitory effects of sulfate on the uptake and volatilization of Se may be reduced substantially if Se is supplied as, or converted to, SeO 3 and/or SeMeth rather than SeO 4.
Abstract: Selenium (Se) removal from polluted waters and soils is especially complicated and highly expensive. Phytoremediation has been suggested as a low-cost, efficient technology for Se removal. Plants remove Se by uptake and accumulation in their tissues, and by volatilization into the atmosphere as a harmless gas. Unraveling the mechanisms of Se uptake and volatilization in plants may lead to ways of increasing the efficiency of the phytoremediation process. The objectives of this study were: (i) to determine the effect of different Se forms in the root substrate on the capacity of some plant species to take up and volatilize Se; (ii) to determine the chemical species of Se in different plant parts after the plants were supplied with various forms of Se; and (iii) to determine the influence of increasing sulfate levels on plant uptake, translocation, and volatilization of different Se species. Plants of broccoli (Brassica oleracea var. botrytis L.), Indian mustard (Brassica juncea L.), sugarbeet (Beta vulgaris L.) and rice (Oryza sativa L.) were grown hydroponically in growth chambers and treated for 1 week with 20 μM Se as Na2SeO4, Na2SeO3 or L-selenomethionine (SeMeth) and increasing sulfate levels. The data show that shoots of SeO4-supplied plants accumulated the greatest amount of Se, followed by those supplied with SeMeth then SeO3. In roots, the highest Se concentrations were attained when SeMeth was supplied, followed by SeO3, then SeO4. The rate of Se volatilization by plants followed the same pattern as that of Se accumulation in roots, but the differences were greater. Speciation analysis (X-ray absorption spectroscopy) showed that most of the Se taken up by SeO4-supplied plants remained unchanged, whereas plants supplied with SeO3 or SeMeth contained only SeMeth-like species. Increasing the sulfate level from 0.25 mM to 10 mM inhibited SeO3 and SeMeth uptake by 33% and 15–25%, respectively, as compared to an inhibition of 90% of SeO4 uptake. Similar results were observed with regard to sulfate effects on volatilization. We conclude that reduction from SeO4 to SeO3 appears to be a rate-limiting step in the production of volatile Se compounds by plants. Inhibitory effects of sulfate on the uptake and volatilization of Se may be reduced substantially if Se is supplied as, or converted to, SeO3 and/or SeMeth rather than SeO4.
440 citations
Cites background from "Use of one‐electron theory for the ..."
...The theory of the K-absorption edge transitions has been clearly discussed and modeled (Kutzler et al. 1980)....
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TL;DR: The XAS speciation analysis indicates that CrO42− is converted in the root to Cr3+ by all plants tested, and a hypothesis for the differential accumulation and identical translocation patterns of the two Cr ions is proposed.
Abstract: Trivalent chromium (Cr3+) is essential for animal and human health, whereas hexavalent Cr (CrO42−) is a potent carcinogen and extremely toxic to animals and humans. Thus, the accumulated Cr in food plants may represent potential health hazards to animals and humans if the element is accumulated in the hexavalent form or in high concentrations. This study was conducted to determine the extent to which various vegetable crops absorb and accumulate Cr3+ and CrO42− into roots and shoots and to ascertain the different chemical forms of Cr in these tissues. Two greenhouse hydroponic experiments were performed using a recirculating-nutrient culture technique that allowed all plants to be equally supplied with Cr at all times. In the first experiment, 1 mg L−1 Cr was supplied to 11 vegetable plant species as Cr3+ or CrO42−, and the accumulation of Cr in roots and shoots was compared. The crops tested included cabbage (Brassica oleracea L. var. capitata L.), cauliflower (Brassica oleracea L. var. botrytis L.), celery (Apium graveolens L. var. dulce (Mill.) Pers.), chive (Allium schoenoprasum L.), collard (Brassica oleracea L. var. acephala DC.), garden pea (Pisum sativum L.), kale (Brassica oleracea L. var. acephala DC.), lettuce (Lactuca sativa L.), onion (Allium cepa L.), spinach (Spinacia oleracea L.), and strawberry (Fragaria × ananassaDuch.). In the second experiment, X-ray absorption spectroscopy (XAS) analysis on Cr in plant tissues was performed in roots and shoots of various vegetable plants treated with CrO42− at either 2 mg Cr L−1 for 7 d or 10 mg Cr L−1 for 2, 4 or 7 d. The crops used in this experiment included beet (Beta vulgaris L. var. crassa (Alef.) J. Helm), broccoli (Brassica oleracea L. var. Italica Plenck), cantaloupe (Cucumis melo L. gp. Cantalupensis), cucumber (Cucumis sativus L.), lettuce, radish (Raphanus sativus L.), spinach, tomato (Lycopersicon lycopersicum (L.) Karsten), and turnip (Brassica rapa L. var. rapifera Bailey). The XAS speciation analysis indicates that CrO42− is converted in the root to Cr3+ by all plants tested. Translocation of both Cr forms from roots to shoots was extremely limited and accumulation of Cr by roots was 100-fold higher than that by shoots, regardless of the Cr species supplied. Highest Cr concentrations were detected in members of the Brassicaceae family such as cauliflower, kale, and cabbage. Based on our observations and previous findings by other researchers, a hypothesis for the differential accumulation and identical translocation patterns of the two Cr ions is proposed.
386 citations
TL;DR: A new approach by exploring robust noncarbon Ti( 0.7)Mo(0.3)O(2) used as a novel functionalized cocatalytic support for Pt that opens a reliable path to the discovery advanced concept in designing new catalysts that can replace the traditional catalyst structure and motivate further research in the field.
Abstract: The slow rate of the oxygen reduction reaction (ORR) and the instability of Pt-based catalysts are two of the most important issues that must be solved in order to make proton exchange membrane fuel cells (PEMFCs) a reality. Additionally, the serious carbon corrosion on the cathode side is a critical problem with respect to the durability of catalyst that limits its wide application. Here, we present a new approach by exploring robust noncarbon Ti0.7Mo0.3O2 used as a novel functionalized cocatalytic support for Pt. This approach is based on the novel nanostructure Ti0.7Mo0.3O2 support with “electronic transfer mechanism” from Ti0.7Mo0.3O2 to Pt that can modify the surface electronic structure of Pt, owing to a shift in the d-band center of the surface Pt atoms. Furthermore, another benefit of Ti0.7Mo0.3O2 is the extremely high stability of Pt/Ti0.7Mo0.3O2 during potential cycling, which is attributable to the strong metal/support interaction (SMSI) between Pt and Ti0.7Mo0.3O2. This also enhances the inher...
355 citations
References
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Book•
01 Jan 1949
TL;DR: The perturbation theory has been applied to many-body problems and applications, such as electron collisions with atoms, collisions between atomic systems, nuclear collisions, and certain aspects of two-body systems under relativistic collisions.
Abstract: Volume II of this work covers many-body problems and applications of the theory to electron collisions with atoms, collisions between atomic systems, nuclear collisions, certain aspects of two-body systems under relativistic collisions, and the use of time-dependent perturbation theory. Despite the amount of work carried out since this book was first published, the underlying theory presented here remains both sound and of practical value to all theoretical physicists.
2,969 citations
TL;DR: In this article, the Hohenberg-Kohn-Sham local density theory is explored in view of recent advances in the theory of the interacting electron gas, and the authors discuss and provide numerical data for the effective exchange-correlation potentials mu xc for ground state problems and Vxc for excitation spectra.
Abstract: The possibilities of the Hohenberg-Kohn-Sham local density theory are explored in view of recent advances in the theory of the interacting electron gas. The authors discuss and provide numerical data for the effective exchange-correlation potentials mu xc for ground state problems and Vxc for excitation spectra. The potential mu xc(r) is written as a factor beta ( rho (r)), which depends on the local density rho (r), times the Kohn-Sham-Gaspar potential mu x=-e2kF/ pi . The factor beta , which is represented by a simple analytical formula, varies between 1 for very high densities and about 1.5 for very low densities, where mu xc thus approaches the Slater approximation. The potential Vxc is given in the form of a table. The explicit predictions of the approximate theories are mapped in their linearized versions. The theory is also developed for the case when the ion cores are treated separately, and the local density approximation is applied only to the valence electrons.
2,045 citations
TL;DR: The main point of the method of Gaspar, Kohn, and Sham is that they derived the approximate exchange correction from an approximate Hamiltonian for the system by varying the spin-orbitals to minimize the average value of this Hamiltonians for the ground state as discussed by the authors.
Abstract: Publisher Summary This chapter discusses statistical exchange-correlation in the self-consistent field. There are two sides to a self-consistent field calculation: the determination of the potential and the solution of Schrodinger's equation for the one-electron problem. The solution of Schrodinger's equation has fortunately advanced far enough through the application of the electronic digital computer so that it can be regarded for most purposes as being a standardized technique. The main point of the method of Gaspar, Kohn, and Sham is that they derive the approximate exchange correction from an approximate Hamiltonian for the system by varying the spin-orbitals to minimize the average value of this Hamiltonian for the ground state. The approximate Hamiltonian has many important and valuable features that are described in the chapter.
874 citations
TL;DR: In this article, two criteria for determining the exchange parameter $\ensuremath{\alpha}$ which occurs in the local-statistical-exchange approximation, an approximation widely used in energy-band and molecular calculations, are examined.
Abstract: We have examined two criteria for determining the exchange parameter $\ensuremath{\alpha}$ which occurs in the $X\ensuremath{\alpha}$ local-statistical-exchange approximation, an approximation widely used in energy-band and molecular calculations. These criteria are (i) adjustment of the statistical total energy to the Hartree-Fock total energy, leading to ${\ensuremath{\alpha}}_{\mathrm{HF}}$, and (ii) satisfaction of the virial theorem, leading to ${\ensuremath{\alpha}}_{\mathrm{vt}}$. We have calculated the values of the parameter $\ensuremath{\alpha}$ corresponding to these two criteria for the neutral atoms H through Nb, and compared them with the values ${\ensuremath{\alpha}}_{min}$ corresponding to the Hartree-Fock total-energy minimization criterion employed earlier by Kmetko and Wood. While the last-mentioned criterion leads to $\ensuremath{\alpha}$ values which show large fluctuations across the periodic table as a function of $Z$, the $\ensuremath{\alpha}$ values obtained by either of the two criteria used in this paper show a systematic variation as a function of $Z$, reflecting the shell structure of the atoms, and varying linearly with $Z$ within the range of $Z$ for which a particular atomic subshell is being filled.
835 citations
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