The phonon dispersion relations of bulk hexagonal boron nitride have been determined from inelastic x-ray scattering measurements and analyzed by ab initio calculations. Experimental data and calculations show an outstanding agreement and reconcile the controversies raised by recent experimental data obtained by electron-energy loss ...
PubMed
Energy Citations Database
IR spectroscopy and ab initio calculations have been applied to the title compounds. Bicyclic acetals were found to exist as mixture of chair and twist-boat conformations, a parent epoxide being in ternary equilibrium. X-ray data on 4-methyl (exo) derivative display a twist-boat form.
NASA Astrophysics Data System (ADS)
We compare ab initio broad spectrum calculations of the K-edge X-ray absorption spectra of copper and molybdenum against accurate experimental measurements and tabulated standards on an absolute scale. Comparisons are also presented for the fine structure in the spectra.
The phonon-dispersion relations of the lightest wurtzite structure compound BeO have been determined from inelastic x-ray scattering (IXS) measurements and analyzed by ab initio calculations. Experimental data and calculations show good agreement and reconcile the existing controversies. The phonon linewidth of the longitudinal-optical ...
The cascade L-shell x-ray emission as an incident polarized and unpolarized monochromatic radiation overpass the 1s ionization threshold is investigated for the metallic Fe by means of moderate resolution, quantitative x-ray spectrometry. A full ab initio theoretical investigation of the L-shell ...
Here we show that the low temperature phase of magnetite is associated with an effective, although fractional, ordering of the charge. Evidence and a quantitative evaluation of the atomic charges are achieved by using resonant x-ray diffraction (RXD) experiments whose results are further analyzed with the help of ab initio calculations ...
Time-resolved x-ray spectroscopy at the Si L edges is used to probe the electronic structure of an amorphous Si foil as it melts following absorption of an ultrafast laser pulse. Picosecond temporal resolution allows observation of the transient liquid phase before vaporization and before the liquid breaks up into droplets. The melting causes changes in the spectrum that match ...
Synergistic synchrotron x-ray absorption experiments using imaging magnetic microspectroscopy, x-ray magnetic circular dichroism, and ab initio calculations on FeCr alloys reveal that the Cr content strongly influences the ferromagnetic microstructure and the Fe magnetic moments. The Cr local structure resolved by ...
A direct calculation of the coherent x-ray scattering spectrum of liquid water under ambient conditions is presented using ab initio density functional theory. The experimental data are compared with the calculated x-ray scattering spectra retrieved from the trajectories of two Car-Parrinello molecular dynamics ...
We present a combined experimental and theoretical study on the Mn3d orbital occupation in orthorhombic DyMnO3 single crystals. We have observed a very strong polarization dependence in the MnL2,3 x-ray absorption spectra, indicative for a distinct anisotropic orbital occupation. Ab initio electronic-structure calculations ...
We present an ab initio theory of core and valence resonant inelastic x-ray scattering (RIXS) based on a real-space multiple-scattering Green�s function formalism and a quasiboson model Hamiltonian. Simplifying assumptions are made that lead to an approximation of the RIXS spectrum in terms of a convolution of an effective ...
Coherent x-ray diffraction microscope, with its spatial resolution limited only by signal-to-noise ratio, has paved a route to a generic nano-scope relieved from crystalline specimens and destructive sample preparation. We advanced it further as a versatile spectro-microscopy. By using stark contrast in x-ray scattering lengths in the vicinity of atomic absorption edges, we ...
We report on the first experimental ab initio reconstruction of an image of a single particle from fluctuations in the scattering from an ensemble of copies, randomly oriented about an axis. The method is applicable to identical particles frozen in space or time (as by snapshot diffraction from an x-ray free electron laser). These fluctuations enhance ...
The total energy of a grain boundary in a transition metal is calculated in an {ital ab} {ital initio} manner. Such calculations are now feasible using a plane-wave basis set provided that an optimally convergent pseudopotential is used. The investigation focuses on resolving two competing atomic models for the {Sigma}=5 (001) twist boundary in gold. It is ...
Sm{sub 2}O{sub 3} was compressed at room temperature up to 44.0 GPa and then decompressed back to ambient pressure. In situ X-ray diffraction was used to monitor the structural changes in the sample. A cubic to hexagonal phase transformation was observed in Sm{sub 2}O{sub 3} for the first time. After decompression back to ambient pressure, the hexagonal phase was not ...
Electromagnetically induced transparency is predicted for x rays in laser-dressed neon gas. The x-ray photoabsorption cross section and polarizability near the Ne K edge are calculated using an ab initio theory suitable for optical strong-field problems. The laser wavelength is tuned close to the transition between ...
This work reports a theoretical x-ray absorption near-edge structure (XANES) spectroscopy study at the Mn K-edge in several Mn3MC (M = Sn, Zn and Ga) compounds. Comparison of the experimental Mn K-edge XANES spectra and theoretical computations based on multiple scattering theory shows that standard single-channel calculations are not able to reproduce the experimental ...
We demonstrate the abilities of elastic x-ray scattering to yield information on dense matter with multiple ion species and on the microscopic mixing in dense materials. Based on partial structure factors from ab initio simulations, a novel approach for the elastic scattering feature is applied to dense hydrogen-beryllium and ...
E-print Network
The proton microprobe for the nondestructive detection of trace elements in IDPs (interplanetary dust particles) is presented. Using the Heidelberg proton microprobe, four IDPs have been analyzed and up to 26 elements were detected. To quantitatively evaluate the proton-induced X-ray spectra, ab initio X-ray yields ...
The formalism and the experimental conditions under which coherent inelastic x-ray scattering from phonons can be utilized to determine the vibrational density of states are presented. The validity of the approach is checked by comparison of results for diamond and MgO with ab initio lattice dynamics calculations and thermodynamic ...
Achieving comprehensive information on thin film lattice dynamics so far has eluded well established spectroscopic techniques. We demonstrate here the novel application of grazing incidence inelastic x-ray scattering combined with ab initio calculations to determine the complete elastic stiffness tensor, the acoustic and low-energy ...
The energy scale of a triple-axis x-ray spectrometer with meV energy resolution based on perfect silicon crystal optics is calibrated, utilizing the most recent determination of the silicon lattice parameter and its thermal expansion coefficient and recording the dispersion of longitudinal acoustic and optical phonons in a diamond single crystal and the molecular vibration ...
Ab initio calculations using SCF approach for and analysis of results of investigation of the electronic structure of the clusters RAn+:[L]k with rare earths or actinides were carried out for the clusters in solids and liquids. Theoretical results for the electronic structure, radial integrals and energy of X- ray ...
A novel code for the analysis of extended x-ray absorption fine structure (EXAFS) data collected in total reflection mode (reflEXAFS) is presented. The procedure calculates the theoretical fine structure signals appearing in the reflectivity spectrum starting from the ab initio EXAFS calculations. These signals are then used in complex ...
We report herein a series of ab initio simulations of water under both static and shocked conditions. We have calculated the coherent x-ray scattering intensity of several phases of water under high pressure, using ab initio Density Functional Theory (DFT). We provide new atomic scattering form ...
DOE Information Bridge
We present the results of a benchmark experiment aimed at validating recent calculation techniques for the emission properties of medium and high-Z multicharged ions in hot plasmas. We use space- and time-resolved M-shell x-ray spectroscopy of a laser-produced gas jet xenon plasma as a primary diagnostic of the ionization balance dynamics. We perform measurements of the ...
The X-ray photoelectron spectra of the inner levels and valence bands of the surfaces of BiFeO3 and Fe2O3 single crystals have been measured using X-ray photoelectron spectroscopy on an ESCALAB 250 X-ray photoelectron microprobe with monochromatization of X-ray radiation of the Al K ? line. The ab initio ...
In this work we present a general theoretical outline for calculating time-dependent x-ray scattering signal changes from first principles. We derive a formalism for the description of atom-atom correlation functions as Fourier transforms of quantum-chemically calculated electron densities and show their proportionality to the molecular form factor. The formalism derived in ...
We propose to extend our state-of-the-art, ab initio XAFS (X-ray absorption fine structure) codes, FEFF. Our current work has been highly successful in achieving accurate, user-friendly XAFS standards, exceeding the performance of both tabulated standards...
National Technical Information Service (NTIS)
Ab initio LCAO-MO-SCF calculations using several basis sets and approximate INDO-MO calculations for methyl nitrate are reported. The eigenvalues and eigenvectors are used to analyze the results of x-ray photoelectron spectroscopic studies of the molecule. Core and valence electron and satellite spectra are reported. Both the theoretical and experimental ...
Ab initio LCAO-MO-SCF calculations using several basis sets and approximate INDO-MO calculations for methyl nitrate are reported. The eigenvalues and eigenvectors are used to analyze the results of x-ray photoelectron spectroscopic studies of the molecule...
By employing the state-of-the-art in situ high-pressure synchrotron x-ray measurements and ab initio modeling, we have resolved atomic-level packing details in a metallic glass as a function of pressure. We demonstrate pronounced changes in atomic size ratio (and correspondingly coordination number) with increasing pressure and the ...
Lattice distortions near impurity atoms in ?-Fe1?x Six alloys (x?0.05 0.06) are studied both experimentally using x-ray diffraction and theoretically by means of ab initio calculations. It is found that the distortions are more complex than experimental data suggest. The displacements of atoms near impurities are not determined by the ...
This paper discusses basics of high performance computing on the example of the Latvian SuperCluster (LASC), installed at the Institute of Solid State Physics of the University of Latvia. The application of LASC to abinitio simulations of x-ray absorption spectra from nanoparticles is considered as a particular case. [Keywords: high performance computing, cluster computing, ...
X-ray-diffraction data have been obtained on Si in a diamond anvil cell to pressures of --50 GPa. Crystallographic data are presented in phase I (cubic, diamond), II (tetragonal, ..beta..-Sn), V (simple hexagonal), VII (hexagonal close-packed), and the metastable phase III (body-centered-cubic (BC8)) and on the coexistence of the phases. Comparison is made between these data ...
deposition on Al(111) - STM FOV: 23 nm. Ti/Al(111) deposited at 400 K. #12;10 FT-IR Spectroscopy - atomic H, time-resolved, high-pressure. � X-ray microprobe � IR micro-spectroscopy � Surface microscopy & energetics. Ab-initio molecular dynamics - surface dynamics. FT-infrared reflection spectroscopy - hydrogen
The comparison of the PBPs and ?-lactamases serine active sites clearly displays their common geometric similarities which could be involved in the acylation mechanism. Nevertheless, recent apo and acylated X-ray structures on one hand and ab initio reaction path models on the other point out the incidence of conformational ...
The methodology of X-ray crystallography has recently been successfully extended to the structure determination of non-crystalline specimens. The phase problem was solved by using the oversampling method, which takes advantage of ''continuous'' diffraction pattern from non-crystalline specimens. Here we review the principle of this newly developed technique and ...
We present non-resonant inelastic x-ray scattering measurements (NRIXS) of the contribution of each initial state orbital in MgO to the dynamic structure factor. We find good agreement with previous x-ray absorption fine structure (XAFS) measurements and with previous electron energy loss spectroscopy (EELS) measurements for the corresponding edges. We ...
Recent work is extending the methodology of X-ray crystallography to the structure determination of noncrystalline specimens. The phase problem is solved using the oversampling method, which takes advantage of ''continuous'' diffraction patterns from noncrystalline specimens. Here we review the principle of this newly developed technique and discuss the ongoing ...
The purpose of this work is to compare the two different procedures to calculate the L(2,3) x-ray absorption spectra of transition-metal compounds: (1) the semi-empirical charge transfer multiplet (CTM) approach and (2) the ab�initio configuration-interaction (CI) method based on molecular orbitals. We mainly focused on the difference in the treatment of ...
Variations in the electronic structure and structural distortion in multiferroic DyMnO3 were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled ...
Variations in the electronic structure and structural distortion in multiferroic DyMnO(3) were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled ...
Improved calculations of Bragg peak intensities near atomic resonance are obtained by including the effect of the local environment around the resonant atoms on the resonant scattering amplitudes ?f=f'+if''. Theoretical absorption cross sections calculated by the ab initio x-ray-absorption code FEFF are used to obtain the imaginary ...
We have calculated the coherent x-ray scattering intensity of several phases of water at 1500 and 2000 K under high pressure, using ab initio Density Functional Theory (DFT). Our calculations span the molecular liquid, ice VII, and superionic solid phases, including the recently predicted symmetrically hydrogen bonded region of the ...
In situ X-ray absorption spectroscopy (XAS) at the Pt L(3) edge is a useful probe for Pt-O interactions at polymer electrolyte membrane fuel cell (PEMFC) cathodes. We show that XAS using the high energy resolution fluorescence detection (HERFD) mode, applied to a well-defined monolayer Pt/Rh(111) sample where the bulk penetrating hard X-rays probe only ...
Coherent X-ray diffraction microscopy is a method of imaging non-periodic isolated objects at resolutions only limited, in principle, by the largest scattering angles recorded. We demonstrate X-ray diffraction imaging with high resolution in all three dimensions, as determined by a quantitative analysis of the reconstructed volume images. These images are ...
Electronic structure heterogeneities are ubiquitous in two-dimensional graphene and profoundly impact the transport properties of this material. Here we show the mapping of discrete electronic domains within a single graphene sheet using scanning transmission X-ray microscopy in conjunction with ab initio density functional theory ...
We report orientation-specific, surface-sensitive structural characterization of colloidal CdSe nanorods with extended X-ray absorption fine structure spectroscopy and ab-initio density functional theory calculations. Our measurements of crystallographically-aligned CdSe nanorods show that they have reconstructed Cd-rich surfaces. They exhibit ...
An NMR structure refinement method for the NMR crystallography of zeolites is presented and demonstrated to give an NMR-determined crystal structure for the zeolite Sigma-2 that is in very good agreement with the single-crystal X-ray diffraction structure. The Si coordinates of the zeolite framework were solved from 29Si double-quantum NMR data obtained at a low magnetic field ...
We have tested approaches for molecular-dynamics simulations of the ion properties in high-energy-density matter. The scheme incorporates quantum corrections within the potentials used in the classical molecular-dynamics simulation. Thus, a significantly larger number of particles in the simulation box as in ab initio simulations can be used. Two types of ...
This work reports a theoretical study of the x-ray absorption near-edge structure spectra at the Cu K edge in several Cu(II) complexes with N -coordinating ligands showing a square-planar arrangement around metal cation. It is shown that single-channel multiple-scattering calculations are not able to reproduce the experimental spectra. The comparison between experimental data and ...
Using X-ray diffraction Ghose et al. [S.K. Ghose, I.K. Robinson, P.A. Bennett, F.J. Himpsel, Surf. Sci. 581 (2005) 199] have recently produced a structural model for the quantum-wire surface Si(5 5 3) Au. This model presents two parallel gold wires located at the step edge. Thus, the structure and the gold coverage are quite different from previous proposals. We present here ...
The coordination structures of U(IV), Np(IV), and Th(IV) in aqueous solution have been determined by studying the X-ray absorption near edge structure (XANES) of the actinide (An) L(3)-edge absorption spectra. The high sensitivity of XANES to the bonding geometry provides an unambiguous determination of the coordination polyhedron. On the basis of the comparison of ab ...
... This study involves: Ab-initio crystal orbitals and polymer orbitals; Ab-initio coupled cluster program; Ab-initio quantum chemical calculations and ...
DTIC Science & Technology
The X-ray damage of the sulfhydryl enzyme malate synthase from yeast has been investigated by physicochemical studies including time-resolved small-angle X-ray scattering. Our previous studies already suggested the role of cysteine-sulfenic acid and disulfides in the damage process and established a simple model for the occurring aggregation. The preceding model is now ...
We propose to extend our state-of-the-art, ab initio XAFS (X-ray absorption fine structure) codes, FEFF. Our current work has been highly successful in achieving accurate, user-friendly XAFS standards, exceeding the performance of both tabulated standards and other codes by a considerable margin. We now propose to add the capability to ...
A sodium calcium borate, NaCaBO3, has been synthesized by the solid-state reaction method and the structure solved from X-ray powder diffraction data. The compound crystallizes in space group Pmmn and has a desired structure type containing isolated planar BO3(3-) anions. Mixed occupancy is found to exist in the Ca site, with partial replacement by Na. One Ca/Na mixed atom and ...
We present a structural analysis of the multilayer graphene/4HSiC(0001) system using surface x-ray reflectivity. We show that graphene films grown on the C-terminated (0001) surface have a graphene-substrate bond length that is very short (1.62 A). The measured distance rules out a weak van der Waals interaction to the substrate and instead indicates a strong bond between the ...
The variation with excitation energy of the line shapes of the Cu K{alpha}{sub 1,2} x-ray spectrum was measured with high energy resolution near the K-shell threshold. Fits with ab initio Dirac-Fock calculated spectra allow us to estimate separately the magnitudes and energy variations of the 3d electron shakeup and shakeoff ...
Small-angle X-ray scattering (SAXS) is a powerful method for obtaining quantitative structural information on the size and shape of proteins, and it is increasingly used in kinetic studies of folding and association reactions. In this minireview, we discuss recent developments in using SAXS to obtain structural information on the unfolded ensemble and early folding ...
The crystal structures and the physical (magnetic, electrical transport and thermodynamic) properties of the ternary compounds CeRhSi2 and Ce2Rh3Si5 (orthorhombic CeNiSi2- and U2Co3Si5-type structures, respectively) were studied over wide ranges of temperature and magnetic field strength. The results revealed that both materials are valence fluctuating systems, in line with previous literature ...
The transition 2p/sup 5/--2p/sup 4/3s and 2p/sup 5/--2p/sup 4/3d in fluorine-like Zn, Ge, and Se have been measured in laser-produced x-ray spectra. The experimental spectral data agree well with ab initio atomic structure calculations based on Hartree-Fock wave functions. Classifications of the F I-like lines in these spectra are ...
In the iron pnictides, the strong sensitivity of the iron magnetic moment to the arsenic position suggests a significant relationship between phonons and magnetism. We measured the phonon dispersion of several branches in the high-temperature tetragonal phase of CaFe{sub 2}As{sub 2} using inelastic x-ray scattering on single-crystal samples. These measurements were compared to ...
X-ray diffraction measurements were carried out for liquid iron near the melting temperature and atomic configurations were constructed from the structure factor S(Q) obtained, by reverse Monte Carlo modeling and Monte Carlo simulation with the effective pair potential deduced by the inverse method. The bond-orientational order parameter ?6 calculated from the atomic ...
The magnetic ground state of the Heusler compound Mn2CoSn was predicted to be nearly half-metallic ferrimagnetic with a high spin polarization by ab initio electronic structure calculations. Mn2CoSn was synthesized, and the magnetic behavior of the compound was studied using a superconducting quantum interference device and x-ray magnetic circular ...
We have measured a series of high-resolution x-ray spectra emitted upon resonant photoexcitation of HCl. The photon energy was tuned across the dissociative 1s?6?* resonance and the Rydberg states converging to the Cl 1s(-1) threshold, and inelastic photon scattering was observed in the region of KL emission lines. Excellent agreement is found between fully ...
We have measured a series of high-resolution x-ray spectra emitted upon resonant photoexcitation of HCl. The photon energy was tuned across the dissociative 1s{yields}6{sigma}* resonance and the Rydberg states converging to the Cl 1s{sup -1} threshold, and inelastic photon scattering was observed in the region of KL emission lines. Excellent agreement is found between fully ...
We have measured a series of high-resolution x-ray spectra emitted upon resonant photoexcitation of HCl. The photon energy was tuned across the dissociative 1s?6?* resonance and the Rydberg states converging to the Cl 1s-1 threshold, and inelastic photon scattering was observed in the region of KL emission lines. Excellent agreement is found between fully ...
The five independent elastic moduli of single-crystalline hexagonal boron nitride (h-BN) are determined using inelastic x-ray scattering. At room temperature the elastic moduli are in units of GPa C{sub 11}=811, C{sub 12}=169, C{sub 13}=0, C{sub 33}=27.0, and C{sub 44}=7.7. Our experimental results are compared with predictions of ab ...
Core-level X-ray photoemission and near-edge X-ray absorption fine structure spectra of 5-methylcytosine, 5-fluorocytosine, and isocytosine are presented and discussed with the aid of high-level ab initio calculations. The effects of the methylation, halogenation, and isomerization on the relative stabilities of ...
High-resolution spectroscopy of a hot tokamak plasma seeded with argon ions and interacting with an energetic, short-pulse neutral hydrogen beam was used to obtain a high-resolution K-shell x-ray spectrum formed solely by charge exchange. The observed K-shell emission of Ar{sup 16+} is dominated by the intercombination and forbidden lines, providing clear signatures of charge ...
High-resolution spectroscopy of a hot tokamak plasma seeded with argon ions and interacting with an energetic, short-pulse neutral hydrogen beam was used to obtain a high-resolution K -shell x-ray spectrum formed solely by charge exchange. The observed K -shell emission of Ar16+ is dominated by the intercombination and forbidden lines, providing clear signatures of charge ...
High-resolution spectroscopy of hot tokamak plasma seeded with argon ions and interacting with an energetic, short-pulse neutral hydrogen beam was used to obtain the first high-resolution K-shell x-ray spectrum formed solely by charge exchange. The observed K-shell emission of Ar{sup 16+} is dominated by the intercombination and forbidden lines, providing clear signatures of ...
Ab initio calculations are performed to explain the discrete transitions in experimental C 1s-NEXAFS (near edge X-ray absorption fine structure) spectra of various benzoic acid derivates. Transition energies and oscillator strengths of the contributing C 1s-{pi}* excitations are computed using the ADC(2) (second-order ...
A 1-day x-ray diffraction experiment on dl-proline monohydrate was performed at 100 kelvin with synchrotron radiation and a charge-coupled device area detection technique. The accuracy of the charge density distribution and of the related electronic properties extracted from these data is comparable or even superior to the accuracy obtained from a 6-week experiment on ...
We have implemented the effect of dynamical core-hole screening, as given by Mahan, Nozi�res, and De Dominicis, in a first-principles based method and applied the theory to the x-ray absorption (XA) spectrum of graphite. It turns out that two of the conspicuous peaks of graphite are well described, both regarding the position, shape, and relative intensity, whereas one peak is absent in the ...
Extended X-ray absorption fine structure (EXAFS) backscattering amplitude and phase functions have been calculated from first principles for K and L edges for nearly every element in the periodic table by using a full curved wave formalism. These functions are tabulated for approximately half of the elements from boron through californium. The functions are calculated for the ...
An x-ray absorption spectroscopy study of several Mn-containing one-dimensional-related hexagonal perovskites BaMnO3 , Ca3ZnMnO6 , and Sr4ZnMn2O9 is reported. A combined analysis of the Mn K -edge extended x-ray absorption fine structure and x-ray absorption near-edge structure has been conducted to investigate a possible disordering caused by the cation interchange between ...
This work reports a theoretical x-ray absorption near-edge structure (XANES) spectroscopy study at the Ti K-edge in TiO(2) rutile. We present detailed ab initio computations of the Ti K-edge XANES spectrum performed within the multiple-scattering framework. An extensive discussion is presented concerning the size of the cluster needed ...
This work reports a theoretical x-ray absorption near-edge structure (XANES) spectroscopy study at the Ti K-edge in TiO2 rutile. We present detailed ab initio computations of the Ti K-edge XANES spectrum performed within the multiple-scattering framework. An extensive discussion is presented concerning the size of the cluster needed to ...
The solvation structure of yttrium (III) in dimethyl sulfoxide has been determined by studying both the extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near edge structure (XANES) regions of the Y K-edge absorption spectra. Although the EXAFS technique provides accurate information about the next neighbors coordination distances, no unambiguous ...
The transverse acoustic excitation modes were detected by inelastic x-ray scattering in liquid Ga in the Q range above 9nm-1 although liquid Ga is mostly described by a hard-sphere liquid. An ab initio molecular dynamics simulation clearly supports this finding. From the detailed analysis for the S(Q,?) spectra with a good statistic ...
For many years, theoretical studies using model and ab initio potentials have predicated the existence of a liquid/liquid phase transition in silicon, based on a continuous change of the liquid A5 structure to A4. In contrast, we report here a quantitative analysis of data from high-energy X-ray diffraction measurements of ...
The Fourier inversion of phased coherent diffraction patterns offers images without the resolution and depth-of-focus limitations of lens-based tomographic systems. We report on our recent experimental images inverted using recent developments in phase retrieval algorithms, and summarize efforts that led to these accomplishments. These include ab-initio reconstruction of a ...
Resonance fluorescence of laser-driven highly charged ions is investigated with regard to precisely measuring atomic properties. For this purpose an ab initio approach based on the Dirac equation is employed that allows for studying relativistic ions. These systems provide a sensitive means to test correlated relativistic dynamics, quantum electrodynamic ...
A different method is proposed to evaluate the electrostatic potential and electric field from x-ray diffraction data by using maximum entropy method. The efficiency of the method is revealed in the application to a ferroelectric material PbTiO{sub 3}. Visualized electrostatic potential and electric field on the charge density distribution give a direct evidence for the ...
The network connectivity in liquid water is revised in terms of electronic signatures of hydrogen bonds (HBs) instead of geometric criteria, in view of recent x-ray absorption studies. The analysis is based on ab initio molecular-dynamics simulations at ambient conditions. Even if instantaneous threadlike structures are observed in the ...
We performed high-resolution inelastic x-ray scattering measurements on a single crystal of hcp cobalt at simultaneous high pressure and high temperature, obtaining 4 of the 5 independent elements of the elastic tensor. Our experiments indicate that the elasticity of hcp-Co is well described within the quasiharmonic approximation and that anharmonic high-temperature effects on ...
Using x-ray absorption spectroscopy, we have studied the effect of pressure on femtometer-scale bond strain due to anisotropic magnetostriction in a thin FeCo film. At 7 GPa local magnetostrictive strain is found to be larger than at ambient, in agreement with spin-polarized ab initio electronic structure calculations, but contrary to ...
We present a series of ab initio calculations of the x-ray absorption cross section (XAS) of ice and liquid water at ambient conditions. Our results show that all available experimental data and theoretical results are consistent with the standard model of the liquid as comprising molecules with approximately four hydrogen bonds. Our simulations of ice XAS ...
The existence of the x-ray magneto-optical Voigt effect is demonstrated. By means of polarization analysis the Voigt rotation and ellipticity of linearly polarized synchrotron radiation are measured at the Co L3 edge upon transmission through an amorphous Co film. The observed x-ray Voigt rotation is about 7.5 degrees /microm. On the basis of ab ...
The existence of the x-ray magneto-optical Voigt effect is demonstrated. By means of polarization analysis the Voigt rotation and ellipticity of linearly polarized synchrotron radiation are measured at the Co L3 edge upon transmission through an amorphous Co film. The observed x-ray Voigt rotation is about 7.5�/?m. On the basis of ab ...
The high pressure structural behavior of nitric acid dihydrate ([H{sub 3}O]{sup +}{center_dot}[NO{sub 3}]{sup -}{center_dot}H{sub 2}O) has been investigated up to 3.8 GPa using single crystal x-ray diffraction and neutron powder diffraction techniques. A new structural phase has been identified above 1.33 GPa and this has been further studied by ab ...
We propose an interface model for Ge and its surface passivating nitride. The ?-Ge3N4(0001)/Ge(111) interface structure does not have dangling bonds and is predicted to be exceptionally stable compared with other possible structures. Band offsets determined using x-ray photoemission spectroscopy study are in agreement with the prediction by first-principles calculations. The ...
X-ray absorption spectroscopy (XAS) is an ideal technique for the investigation of the local structure in materials and in particular around dopant species in semiconducting crystals. This experimental technique permits the quantitative determination of structural parameters such as the bond distances and number of neighbors that are fundamental for understanding the ...
In Ge2Sb2Te5 (GST), the prototype phase-change alloy for data storage, in situ x-ray diffraction experiments reveal a pressure-induced crystalline-amorphous-crystalline transition sequence, all at the same fixed composition and in one experimental cycle. A body-centered-cubic polymorph is discovered at high pressures; the formation of this phase is attributable to its high ...
We calculate the dynamic structure factor S(k,?) of liquid Ge (l-Ge) at temperature T=1250 K, and of amorphous Ge (a-Ge) at T=300 K, using ab initio molecular dynamics. The electronic energy is computed using density-functional theory, primarily in the generalized gradient approximation, together with a plane-wave representation of the wave functions and ...
We have studied the liquid surface of sodium with extensive ab initio molecular dynamics simulations based on ensemble density-functional theory. We find clear evidence of layering in the direction perpendicular to the surface that persists to temperatures more than 100 K above the melting point. We also observe clear Friedel oscillations in the electronic ...
The L2,3 x-ray absorption near-edge structures (XANES) and electron energy loss near-edge structures (ELNES) of 3d transition metal (TM) oxides are systematically calculated by the ab initio charge transfer multiplet (CTM) method using fully relativistic molecular spinors on the basis of density-functional theory. The electronic ...
Three-dimensional low-resolution models of the biochemically and biotechno- logically significant enzyme cellobiose dehydrogenase (CDH) were predicted by advanced modeling approaches based on experimental one-dimensional low-resolution small-angle x-ray scattering (SAXS) data. In particular, the ab initio modeling program DAMMIN by ...
... Title : Chalcopyrite Magnetic Semiconductors: An Ab-Initio Study of Their Structural, Electronic and Magnetic Properties. ...
... from federally funded research, testing and training ... for Research Development Test and Evaluation ... COMPENDIUM OF AB INITIO CALCULATIONS ...
... Accession Number : ADA219907. Title : An Ab Initio Study of the Geometry and Rotational Barrier of 4- Phenylimidazole. ...
... from federally funded research, testing and training ... and agencies for Research Development Test and Evaluation ... Title : Ab Initio Calculations of the ...
... Title : Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. ...
... Title : AB Initio Quantum Chemical Investigations of Solubilities in Supercritical Solutions. Descriptive Note : Conference Paper,. ...
We have calculated the coherent x-ray scattering intensity of several phases of water under high pressure using the ab initio density functional theory (DFT). Our calculations span the molecular liquid, ice VII, and superionic solid phases, including the recently predicted symmetrically hydrogen bonded region. We compute simulated ...
We have determined the high-pressure crystal-structure of propionic acid, including the calculated positions of the hydrogen atoms, using a combination of single-crystal x-ray diffraction techniques and ab initio density functional calculations. We find that a previously unobserved triclinic P bar 1 high-pressure phase and the ...
Recent developments in the understanding of the biosynthesis of the active site of the nitrogenase enzyme, the structure of the iron centre of [Fe]-hydrogenase and the structure and biomimetic chemistry of the [FeFe] hydrogenase H-cluster as deduced by application of X-ray spectroscopy are reviewed. The techniques central to this work include X-ray absorption spectroscopy ...
Most tokamak-based reactor concepts require the use of noble gases to form either a radiative mantle or divertor to reduce conductive heat exhaust to tolerable levels for plasma facing components. Predicting the power loss necessary from impurity radiation is done using electron temperature-dependent ``cooling-curves'' derived from ab initio atomic physics ...
The speciation and quantification of sulfur species based on sulfur K-edge x-ray absorption spectroscopy is of wide interest, particularly for biological and petroleum science. These tasks require a firm understanding of the sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of relevant species. To this end, we have examined the gas phase ...
Structural investigations of the short range order around iridium and oxygen ions in nanocrystalline iridium oxide thin films, prepared by dc magnetron sputtering technique, were performed by x-ray absorption spectroscopy. The Ir L3-edge extended x-ray absorption fine structure and the O K-edge x-ray absorption near edge structure signals were measured at ...
The sign, magnitude, and range of the exchange couplings between pairs of Mn ions is determined for (Ga,Mn)N and (Ga,Mn)N:Si with x?3%. The samples have been grown by metalorganic vapor phase epitaxy and characterized by secondary-ion mass spectroscopy; high-resolution transmission electron microscopy with capabilities allowing for chemical analysis, including the annular dark-field mode and ...
... Title : AB Initio Study of the Electronic Magnetic Circular Dichroism ... functions are determined using as initio quantum chemical techniques including ...
The structure of a Zr{sub 73}Pt{sub 27} metallic glass, which forms a Zr{sub 5}Pt{sub 3} (Mn{sub 5}Si{sub 3}-type) phase having local atomic clusters with distorted icosahedral coordination during the primary crystallization, has been investigated by means of x-ray diffraction and combining ab initio molecular-dynamics (MD) and reverse Monte Carlo (RMC) ...
Due to recent advances in methods and computers, the accuracy of ab calculations has reached a point
NASA Technical Reports Server (NTRS)
This thesis addresses the electronic structure of molecules and solids using resonant X-ray emission and photoemission spectroscopy. The use of monochromatic synchrotron radiation and the improved performance of the instrumentation have opened up the possibility of detailed analyses of the response of the electronic systems under interaction with X-rays. The experimental ...
Over the past two decades dramatic progress has been made in the development of the theory of x-ray and electron spectroscopies, e.g., x-ray absorption spectra (XAS), core-level x-ray photoemission spectroscopy (XPS), x-ray photoelectron diffraction (XPD), etc. A revolutionary advance was the development of efficient and accurate ...
The floating-zone furnace method was used to synthesize single crystals of the fluorite-related delta-Bi{sub 2}O{sub 3}-type phase Bi{sub 38}Mo{sub 7}O{sub 78} for the first time. Single crystal synchrotron X-ray diffraction data, in conjunction with ab initio (density functional theory) calculations, were used to solve, optimize, and ...
We performed high-pressure studies and ab initio calculations of titanium hydride (TiH{sub 2}), an important compound in hydrogen storage research. In situ, synchrotron x-ray diffraction studies were carried out in two separate compression runs: the first up to 19 GPa in quasihydrostatic conditions and the second up to 90 GPa in ...
We performed high-pressure studies and ab initio calculations of titanium hydride (TiH2), an important compound in hydrogen storage research. In situ, synchrotron x-ray diffraction studies were carried out in two separate compression runs: the first up to 19 GPa in quasihydrostatic conditions and the second up to 90 GPa in ...
The band structure of hexagonal boron nitride (BN) has been calculated using an [ital ab] [ital initio] linear combination of pseudoatomic-orbitals method. The calculated band structure confirms a previous finding that this material is an indirect band-gap insulator and has two empty interlayer bands. Projected densities of states are compared with the ...
Determining the structure of a small molecule bound to a biological receptor (e.g., a protein implicated in a disease state) is a necessary step in structure-based drug design. The preferred conformation of a small molecule can change when bound to a protein, and a detailed knowledge of the preferred conformation(s) of a bound ligand can help in optimizing the affinity of a molecule for its ...
PubMed Central
Traditionally, one has two ways of calculating ab initio x-ray and electron absorption spectra. Band structure calculations can treat periodic materials such as crystals, however, when a core hole is introduced and treated with a supercell approximation, unphysical interactions are often introduced. Real space calculations on the other ...
Phenothiazine and its derivatives have been investigated because of their interesting pharmacological activity and their potential use in solar energy applications. Raman spectra of phenothiazine and its radical cation were obtained. Hartree-Fock (HF) and density functional theory (DFT) ab initio calculations were performed to find optimized structures and ...
Ionic amorphous oxide semiconductors (IAOSs) are new materials for flexible thin film transistors that exhibit field-effect mobilities of {approx}10 cm{sup 2} V{sup -1} s{sup -1} [K. Nomura et al., Nature 488, 432 (2004)]. The local coordination structure in an IAOS, In-Ga-Zn-O (a-IGZO), was examined using extended x-ray absorption fine structure analysis combined with ...
We report results of a comprehensive study of liquid boron with x-ray measurements of the atomic structure and dynamics coupled with ab initio molecular dynamics simulations. There is no evidence of survival into the liquid of the icosahedral arrangements that characterize the crystal structures of boron but many atoms appear to adopt a geometry ...
Crystalline polyethylene was investigated under pressure between 0 and 40 GPa, up to 280 deg. C, by means of synchrotron x-ray powder diffraction and ab initio calculations. A rich polymorphism was unveiled, consisting of two new high-pressure monoclinic phases, in addition to the well-known orthorhombic one, which appear reversibly, ...
The IR, Raman and NMR spectra of 3-aminomethylene-2,4-pentanedione (AMP) H2NCHC(COCH3)2 were measured. According to the NMR spectra in chloroform and more polar DMSO at room temperature, the sample exists as single entity. On the other hand vibrational spectra revealed that in less polar solutions AMP exists as two conformers with EZ or ZZ orientation of acetyl groups whereas in more polar solvent ...
Solid-state (35)Cl NMR (SSNMR) spectroscopy is shown to be a useful probe of structure and polymorphism in HCl pharmaceuticals, which constitute ca. 50% of known pharmaceutical salts. Chlorine NMR spectra, single-crystal and powder X-ray diffraction data, and complementary ab initio calculations are presented for a series of HCl local ...
Theoretical calculations of vibrational effects in x-ray absorption spectra typically employ semi-phenomenological models, e.g. empirical force constants or correlated Debye or Einstein models. Instead we introduce an efficient and generally applicable ab initio approach based on electronic structure calculations of the dynamical matrix together with the ...
Fluid Hg undergoes a metal-nonmetal (M-NM) transition when expanded toward a density of around 9�g�cm(-3). We have performed ab initio molecular dynamics simulations for several thermodynamic states around the M-NM transition range and the associated static, dynamic and electronic properties have been analyzed. The calculated static structure shows a ...
O1s x-ray absorption spectroscopy (XAS) in conjunction with photoelectron spectroscopy has been used to explore the conduction-band edge of single crystalline and nanostructured anatase TiO2 . The experiments are supported by ab initio density-functional calculations in which both the initial and core hole final states are ...
We have used the orbital-free ab initio molecular dynamics method to study the phenomenon of surface freezing in a liquid Ga-Tl alloy (nominal Tl concentration of 0.14). Several thermodynamic states are considered from a high temperature of 675 K to a low temperature of 350 K. At the higher temperature the Tl atoms segregate to the surface and form a ...
A new technique of 3D local structure refinement using full-potential X-ray absorption near edge structure (XANES) analysis is proposed and demonstrated in application to metalloorganic complexes of Ni. It can be applied to determine local structure in those cases where the muffin-tin approximation used in most full multiple scattering schemes fails. The method is based on the ...
This work reports a theoretical study of the x-ray absorption near-edge structure spectra at the Cu K edge in several Cu(II) complexes with N-coordinating ligands showing a square-planar arrangement around metal cation. It is shown that single-channel multiple-scattering calculations are not able to reproduce the experimental spectra. The comparison between experimental data and ...
We report a study on several static, dynamic, and electronic properties of liquid Hg at room temperature. We have performed ab initio molecular dynamics simulations using Kohn-Sham density functional theory combined with a nonlocal ultrasoft pseudopotential. The calculated static structure shows good agreement with the available experimental data. We ...
We have performed ab initio molecular dynamics simulation of Cu64Zr36 alloy at descending temperatures (from 2000 K to 400 K) and discussed the evolution of short-range order with temperature. The pair-correlation functions, coordination numbers, and chemical compositions of the most abundant local clusters have been analyzed. We found that icosahedral ...
The ab initio structure determination of a novel unconventional noncentro-symmetric superconductor Mg{sub 10}Ir{sub 19}B{sub 16} (T{sub c} = 5 K) has been performed using a method that involves a combination of experimental data and calculations. Electron diffraction, X-ray powder diffraction, phase estimation routines, quantum ...
... AB-INITIO SIMULATION OF a/2110> ... 4. TITLE AND SUBTITLE AB-INITIO SIMULATION OF a/2110> SCREW DISLOCATIONS γ-TiAl 5c. ...
... ADP012740 TITLE: Ab Initio Study on Spin Polarization of III-V Compound Tips ... Ab initio study on spin polarization of III-V compound tips ...
Ab initio electronic structure methods can supplement CALPHAD in two major ways for subsequent applications to stability in complex alloys. The first one is rather immediate and concerns the direct input of ab initio energetics in CALPHAD databases. The o...
...with this part. The certificate shall be void ab initio for those vehicles causing the...issued, and the certificate may be deemed void ab initio. (C) The manufacturer...with this part. The certificate shall be void ab initio for those vehicles causing...
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In a study of type-I Ba8AlxGe46?x clathrates for 4?x?16 , several samples with different stoichiometric compositions were prepared and measured. Here we report wavelength dispersion spectroscopy, powder x-ray diffraction and resistivity measurements, coupled with first-principles calculations. The lattice constant and vacancy count showed linear behavior for low Al content, ...
The transverse acoustic excitation modes were detected by inelastic x-ray scattering in liquid Ga in the Q range above 9 nm-1 although liquid Ga is mostly described by a hard-sphere liquid. An ab initio molecular dynamics simulation clearly supports this finding. From the detailed analysis for the S( Q,?) spectra with a good statistic ...
We report the discovery of a post-cotunnite phase of TiO_{2} by both density-functional ab�initio calculations and high-pressure experiments. A pressure-induced phase transition to a hexagonal Fe_{2}P-type structure (space group P6[over �]2m) was predicted to occur at 161�GPa and 0�K and successfully observed by in�situ synchrotron x-ray ...
We report the discovery of a post-cotunnite phase of TiO2 by both density-functional ab initio calculations and high-pressure experiments. A pressure-induced phase transition to a hexagonal Fe2P-type structure (space group P6�2m) was predicted to occur at 161 GPa and 0 K and successfully observed by in situ synchrotron x-ray ...
Despite of its technological relevance, the self assembly of alkyl-trichlorosilanes onto oxidized metal or semiconductor surfaces is still not fully understood. Phenomena, such as island formation and polymerization, hamper the formation of densely packed and well-ordered self assembled monolayers (SAM). To elucidate the influence of the distribution of OH groups on the surface, we have used ...
We report a fully relativistic close-coupling calculation of the electron impact excitation of Ni xix to derive the 3C/3D line intensity ratio, with an uncertainty of 5%. Convergence of the calculation with respect to both channel coupling effects and the many interacting Rydberg series of resonances has been achieved. New measurements in an electron beam ion trap agree with our calculation. We ...
Synthesis, spectroscopic and structural study of trans- and cis-(�)-3-phenyl-4-(pyrrolidine-1-carbonyl)-isochroman-1-ones is performed in order to obtain the correlation between the crystal structure and spectroscopic properties of both isomers in solid-state. The methods such as single crystal X-ray diffraction, conventional and linear-polarized IR-spectroscopy, ...
Synchrotron x-ray diffraction experiments on compressed platinum-hydrogen mixtures reveal the formation of platinum hydride at a pressure of 27(1) GPa at room temperature. This compound exhibits two phases, PtH-I and PtH-II, coexisting up to the pressure of 42 GPa, above which the single phase of PtH-II is observed. Pt atoms in the PtH-II phase are shown to form a hexagonal ...
The effects of high pressure on cyanuric chloride (C(3)N(3)Cl(3)), a remarkable crystal structure dominated by halogen bonds, have been studied by synchrotron X-ray diffraction and Raman spectroscopy in a diamond anvil cell. The results of high pressure experiments revealed that there was no obvious phase transition up to 30 GPa, indicating that halogen bonding is an effective ...
Artificial structuring of quasi-two dimensional correlated electron thin films and heterointerfaces offers an arena to discover innovative functionalities by harnessing electronic and orbital degrees of freedom. To harness this potential understanding of how structurally linked correlated electronic responses are modified through epitaxial constraints at the substrate--film hetero-interface is ...
The iron phosphate, Fe(H{sub 2}PO{sub 4}){sub 3}, was synthesized through a precipitation route by means of acidic media. As the compound is highly hygroscopic, the structure was solved ab initio by powder X-ray diffraction under nitrogen flow at room temperature and 200 deg. C. This phase is antiferromagnetic below 30 K. It converts ...
X-ray free-electron lasers (XFEL) are revolutionary photon sources, whose ultrashort, brilliant pulses are expected to allow single-molecule diffraction experiments providing structural information on the atomic length scale of nonperiodic objects. This ultimate goal, however, is currently hampered by several challenging questions basically concerning sample damage, Coulomb ...
Self assembled monolayers (SAM) of ?-functionalized mercaptobiphenyls (?-MBP) are stable, molecularly engineered ultrathin organic films, which can be used for the design of model surfaces with well-defined chemical and physical properties. For example, the number and distribution of terminal hydroxyl groups can be tailored to study water-surface interactions or the chemisorption of organic ...
Binding of citrate and phosphocitrate to calcium oxalate monohydrate crystals has been studied using scanning electron microscopy (SEM) and molecular modeling. Phosphocitrate structure has been resolved using low temperature X-ray analysis and ab initio computational methods. The (-1 0 1) crystal surface of calcium oxalate monohydrate ...
The role of the nitrogen doping in the stabilizing the nanocrystalline cubic phase of zirconia films fabricated by nitrogen beam assisted deposition (IBAD) is investigated. The IBAD zirconia films have diameters three times larger than those previously reported in a sol-gel method. Confocal Raman spectroscopy study indicates that the atomic structure of these IBAD zirconia films evolve from cubic ...
We report a joint experimental and theoretical study on high pressure structures of nanoporous mayenite (12CaO[middle dot]7Al(2)O(3)). A pressure-induced amorphization was identified at ?13 GPa by in situ high pressure x-ray experiments. The amorphous product can be decompressed to ambient conditions. Ab initio calculations reveal that ...
We report a joint experimental and theoretical study on high pressure structures of nanoporous mayenite (12CaO.7Al2O3). A pressure-induced amorphization was identified at ~13 GPa by in situ high pressure x-ray experiments. The amorphous product can be decompressed to ambient conditions. Ab initio calculations reveal that the ...
We report phonon densities of states (DOS) of iron measured by nuclear resonant inelastic x-ray scattering to 153 gigapascals and calculated from ab initio theory. Qualitatively, they are in agreement, but the theory predicts density at higher energies. From the DOS, we derive elastic and thermodynamic parameters of iron, including ...
An ab initio Hartree-Fock approach aimed at directly obtaining the localized orthogonal orbitals (Wannier functions) of a crystalline insulator is described in detail. The method is used to perform all-electron calculations on the ground states of crystalline lithium fluoride and lithium chloride, without the use of any pseudopotentials or model ...
The existence of the x-ray magneto-optical Voigt effect is demonstrated. By means of polarization analysis the Voigt rotation and ellipticity of linearly polarized synchrotron radiation are measured at the Co L{sub 3} edge upon transmission through an amorphous Co film. The observed x-ray Voigt rotation is about 7.5{sup o}/{mu}m . On the basis of ab ...
We have designed and synthesized a pyridine-based tripodal anchor unit to construct a single-molecule junction with a gold electrode. The advantage of tripodal anchoring to a gold surface was unambiguously demonstrated by cyclic voltammetry measurements. X-ray photoelectron spectroscopy measurements indicated that the ? orbital of pyridine contributes to the physical ...
The high resolution sulfur K..beta.. emission in fluorescence and sulfur K absorption of thiophene (C/sub 4/H/sub 4/S) were measured with a double crystal spectrometer. The sulfur K..beta.. emission spectrum was analyzed by comparison with complementary spectral data and with MNDO and ab initio (STO-3G) MO calculations. A tentative assignment of the ...
Our recent inelastic X-ray scattering (IXS) experiments on several non-simple liquid metals have revealed characteristic common features in the collective dynamics. 1) Clear indications for propagating phonon modes were found as in simple liquid metals as liquid alkalis. 2) They exhibit a positive dispersion of about 20 % (except in liquid Ge) again as in liquid simple metals. ...
We identify by ab initio calculations an orthorhombic carbon polymorph in Pnma symmetry that has the lowest enthalpy among proposed cold-compressed graphite phases. This new phase contains alternating zigzag and armchair buckled carbon sheets transformed via a one-layer by three-layer slip mechanism. It has a wide indirect band gap and a large bulk modulus ...
Using ab initio thermodynamics we compile a phase diagram for the surface of Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto ignored polar termination with octahedral iron and oxygen forming a wavelike structure along the [110] direction is identified as the lowest energy configuration over a broad range of oxygen gas-phase ...
We present a structural analysis of the graphene-4HSiC(0001) interface using surface x-ray reflectivity. We find that the interface is composed of an extended reconstruction of two SiC bilayers. The interface directly below the first graphene sheet is an extended layer that is more than twice the thickness of a bulk SiC bilayer ({approx}1.7 {angstrom} compared to 0.63 ...
We study the relation between hydrogen bonding and the vibrational frequency spectra of water on the (110) surface of rutile (α-TiO2) with three structural layers of adsorbed water. Using ab-initio molecular dynamics simulations at 280, 300 and 320K, we find strong, crystallographically-controlled adsorption sites, in general agreement with synchrotron ...
By compressing elemental silicon and hydrogen in a diamond anvil cell, we have synthesized polymeric silicon tetrahydride (SiH(4)) at 124 GPa and 300 K. In situ synchrotron x-ray diffraction reveals that the compound forms the insulating I4(1)/a structure previously proposed from ab initio calculations for the high-pressure phase of ...
By compressing elemental silicon and hydrogen in a diamond anvil cell, we have synthesized polymeric silicon tetrahydride (SiH4) at 124 GPa and 300 K. In situ synchrotron x-ray diffraction reveals that the compound forms the insulating I41/a structure previously proposed from ab initio calculations for the high-pressure phase of ...
The electronic structure of Croconic Acid in the condensed phase has been studied by comparing core level and valence band x-ray photoelectron spectroscopy experiments and first principles density functional theory calculations using the Heyd-Scuseria-Ernzerhof screened hybrid functional and the GW approximation. By exploring the photoemission spectra for different deposition ...
We introduce a thermodynamical model based on the two-temperature approach in order to fully understand the dynamics of the coherent A(1g) phonon in laser-excited bismuth. Using this model, we simulate the time evolution of (111) Bragg peak intensities measured by Fritz et al. [Science 315, 633 (2007)] in femtosecond x-ray diffraction experiments performed on a bismuth film ...
We introduce a thermodynamical model based on the two-temperature approach in order to fully understand the dynamics of the coherent A1g phonon in laser-excited bismuth. Using this model, we simulate the time evolution of (111) Bragg peak intensities measured by Fritz et al. [Science 315, 633 (2007)SCIEAS0036-807510.1126/science.1135009] in femtosecond x-ray diffraction ...
We performed high-resolution inelastic x-ray scattering measurements on a single crystal of hcp cobalt at simultaneous high pressure and high temperature, deriving 4 of the 5 independent elements of the elastic tensor. Our experiments indicate that the elasticity of hcp-Co is well described within the frame of a quasi-harmonic approximation and that anharmonic high-temperature ...
The phonon densities of states of body-centered-cubic Fe-V alloys across the full composition range were studied by inelastic neutron scattering, nuclear resonant inelastic x-ray scattering, and ab initio calculations. The average phonon energy followed the inverse of the electronic heat capacity and the inverse of the electronic ...
Ab initio random structure searching and single-crystal x-ray diffraction have been used to determine the full structures of three phases of lithium, recently discovered at low temperature above 60 GPa. A structure with C2mb symmetry, calculated to be a poor metal, is proposed for the oC88 phase (60-65 GPa). The oC40 phase (65-95 GPa) ...
High-pressure methods were applied to investigate the structural stability and hydrogen bonding of polar molecules of iodoform by synchrotron radiation X-ray diffraction and Raman spectra measurements, respectively. Up to a pressure of 40 GPa, no phase transitions were observed. The discontinuous frequency shift of the C-H stretching band is believed to be related to the ...
Small-angle x-ray scattering data on the unliganded full-length fully glycosylated HIV-1 gp120, the soluble CD4 (domains 1-2) receptor and their complex in solution are presented. Ab initio structure restorations using these data provides the first look at the envelope shape for the unliganded and the complexed gp120 molecule. Fitting ...
X-ray absorption fine structure (XAFS) data from copper, gold, and germanium are analyzed in the framework of the model-independent Bayes-Turchin approach. Compared to earlier treatments, we also obtain spring constants, besides shell radii, Debye-Waller (DW) parameters, and anharmonicity parameters. The use of spring constants instead of DW parameters reduces considerably the ...
Long viewed as a topic in classical physics, ferroelectricity can be described by a quantum mechanical ab initio theory. Thin-film nanoscale device structures integrated onto Si chips have made inroads into the semiconductor industry. Recent prototype applications include ultrafast switching, cheap room-temperature magnetic-field detectors, piezoelectric ...
The first-principles calculations were performed for various structures of IrN2 as candidates of the new phase which was recently synthesized under high pressure. It was found that the monoclinic structure is the most stable and shows higher bulk modulus than pyrite PtN2 . The simulated x-ray diffraction pattern agrees well with the experimental one. The positive formation ...
We present a comparison between FeK -edge x-ray absorption spectra of carbonmonoxy-myoglobin and its simulation based on density-functional theory determination of the structure and vibrations and spectral simulation with multiple-scattering theory. An excellent comparison is obtained for the main part of the molecular structure without any structural fitting parameters. The ...
