... This study involves: Ab-initio crystal orbitals and polymer orbitals; Ab-initio coupled cluster program; Ab-initio quantum chemical calculations and ...
DTIC Science & Technology
NMR chemical shifts for an L-alanine molecular crystal are calculated using ab initio plane wave density functional theory. Dynamical effects including anharmonicity may be included by averaging chemical shifts over an ensemble of structural configurations generated using molecular dynamics (MD). The time scales ...
PubMed
NASA Astrophysics Data System (ADS)
... crystal structures which are ordered superstructures of a parent disordered phase; a highly reliable statistical mechanical method (CVM) has now ...
A systematic method for approximating the ab initio electronic energy of crystal lattices has been improved by the incorporation of long range electrostatic and dispersion interactions. The effect of these long range interactions on the optimization of the crystal structure is reported. The ...
Ab-initio quantum chemical investigations of the mechanism of cationic polymerization; Development, implementation testing of theoretical procedures for prediction of crystal structures and densities; Ab-initio quantum chemical MODPOT/VRDDO/MERGE calculat...
National Technical Information Service (NTIS)
Contents: Ab-initio quantum chemical investigations of the mechanism of cationic polymerization; Development of theoretical procedures for prediction of crystal structures and densities; Ab-initio quantum chemical MODPOT/VRDDO/MERGE calculations on nitro-...
Solid State Nuclear Magnetic Resonance (NMR) is a powerful tool in crystallography when combined with theoretical predictions. So far, empirical calculations of spectra have been employed for an unambiguous identification. However, many complex systems are outside the scope of these methods. Our implementation of ultrasoft and projector augmented wave pseudopotentials within ...
A new algorithm, MEDIC (Maximum Entropy Direct Inversion of Crystallographic Data), is presented that provides a direct method of inverting the observed integrated intensities in a diffraction experiment to yield the scattering density within a unit cell....
... Ab initio study on atomic structures and physical properties of CdSe quantum nanodots ... Figure 2. Diagram of covered nanodots. ...
... Title : Ab Initio Study on Atomic Structures and Physical Properties of CdSe Quantum Nanodots. Descriptive Note : Final rept. ...
... from federally funded research, testing and training ... agencies for Research Development Test and Evaluation ... Title : Ab Initio Study of the Structure ...
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...
A novel density modification method is applied for the first time to phase reconstruction of x-ray single crystal data of quasicrystals. The structure of icosahedral Zn-Mg-Ho quasicrystals has been determined by means of this ab initio structure determination within a framework of a 6D ...
Raman spectra of thin solid electrolyte films obtained by sputtering a Li2SO4 target in nitrogen plasma are measured and compared to ab initio electronic structure calculations for clusters composed of 28 atoms. Agreement between measured and calculated spectra is obtained only when some oxygen atoms are replaced by nitrogen atoms and ...
... Title : Structure of Perfluoromethanimine by Microwave, Infrared, and Raman Spectroscopy, Electron Diffraction, and ab Initio Methods,. ...
... nightmares for traditional quantum chemical approaches for optimizing structures of such ... an unbiased manner with ab initio forces. ...
developed by Perdew et al.30 and norm-conserving pseudopotentials. In static calculations carried out of anatase, we used a 4�4�2 Monkhorst�Pack mesh. The ab initio metadynamics was carried out using the CPMD code (CPMD V3.9 Copyright IBM Corp 1990�2004, Copyright MPI f�ur Festk�orperforschung Stuttgart 1997
E-print Network
The results of ab initio slab calculations of surface relaxations, rumplings and charge distribution for the different terminations of the MgF2 (011) and (111) polar surfaces are presented and discussed. We have employed the computer code CRYSTAL with the Gaussian basis set and the hybrid B3PW exchange-correlation functional. Despite ...
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 other way, more involved, is the ...
DOE Information Bridge
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 ...
Advances in materials science and molecular biology followed rapidly from the ability to characterize atomic structure using single crystals. Structure determination is more difficult if single crystals are not available. Many complex inorganic materials that are of interest in nanotechnology have no periodic ...
We present the photoluminescence spectra of ?-glycine, L-alanine, and L-asparagine crystals. They are broad and structured, comprising green to ultraviolet emission in the 1.75-3.60 eV range. Absorption measurements show that the band gap energies of the crystals are of the order of 5.0 eV. Ab ...
Electronic structure of RNi{sub 5} (R=Nd, Sm, Eu, Gd) and SmCo{sub 5} compounds is calculated using the FLAPW method. The parameters of the effective crystal field hamiltonian acting on 4f states of the rare-earth atom are then determined from the nonspherical part of the crystal potential.
Energy Citations Database
This study involves: Ab-initio crystal orbitals and polymer orbitals; Ab-initio coupled cluster program; Ab-initio quantum chemical calculations and electrostatic molecular potential contour maps for cationic polymerization; Prediction of crystal density;...
Scientists have long pondered why the simple cubic structure is so rarely seen in nature. Only one element forms the simple cubic structure: polonium. There are `proofs' dating back to 1954 that the simple cubic lattice should be unstable. We will attempt to address the question of why polonium takes the simple cubic structure by means ...
Using the state-of-the-art ab initio electronic structure calculations, we explain why ?-Po prefers the simple cubic structure (it is due to the relativistic mass-velocity and Darwin terms), elucidate its extreme elastic anisotropy (this is an intrinsic property of the simple cubic crystal ...
We compute the equilibrium crystal structure and phase stability of iron at the ?(bcc)-?(fcc) phase transition as a function of temperature, by employing a combination of ab initio methods for calculating electronic band structures and dynamical mean-field theory. The magnetic correlation ...
By modeling ?-Zn4Sb3 material as a Zn36Sb30 crystal with defects, the crystal structure and thermal properties of ?-Zn4Sb3 are studied by ab initio method to explain its extremely low thermal conductivity at moderate temperature. The formation and migration energies of defects are calculated ...
The detailed molecular structure of methyl phosphonate, the simplest phosphorus ester, was determined by ab initio quantum-chemical calculations in a variety of basis sets. Computed properties include the optimized structure, dipole moment, number and rel...
Alacranite, As(8)S(9), has been studied by a combined approach based on micro-Raman measurements and ab initio molecular dynamics simulations, with the Car-Parrinello method. The structure of this arsenic sulfide mineral consists of an ordered packing of As(4)S(4) and As(4)S(5) cagelike molecules, with a topology closely resembling ...
Detailed ab initio studies on the electronic structure and optical properties of crystalline strontium azide and barium azide have been performed using density functional theory (DFT) within the generalized gradient approximation (GGA). Relaxed crystal structures compare well with experimental ...
Using the Kernel Energy Method we apply ab initio quantum mechanics to study the relative importance of weak and strong interactions (including hydrogen bonds) in the crystal structures of the title compounds TDA1 and RangDP52. Perhaps contrary to widespread belief, in these compounds the weak interaction energies, ...
PubMed Central
The point charge model is used to calculate the crystal structure of sulfuric acid (H2SO4) with the 6-31 G basis set. The point charge model accurately reproduces the structural trends which occur in transforming from the gas to the solid phase. The calcu...
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 ...
Quantum-mechanical molecular dynamics have been used to investigate structural and physical properties of the 1/1 approximant of the icosahedral Al-Cu-Fe quasicrystal. Particular local structural arrangements of atoms, referred to here as clusters, have been analyzed with respect to their properties within the crystal ...
ABSTRACT: In this article, the authors reported a theoretical study of structural and electronic properties of PbTe inclusions in CdTe matrix as well as CdTe nano-clusters in PbTe matrix. The structural properties are studied by ab initio methods. A tight-binding model is constructed to calculate the electron ...
In this article, the authors reported a theoretical study of structural and electronic properties of PbTe inclusions in CdTe matrix as well as CdTe nano-clusters in PbTe matrix. The structural properties are studied by ab initio methods. A tight-binding model is constructed to calculate the electron density of ...
We have investigated the electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ [at room temperature (RT) and 100 K] and TSeF-TCNQ (RT), which have isomorphic crystal structure, by an ab initio plane-wave pseudopotential band calculation. To express the exchange and ...
In the equilibrium immiscible Ru-Pd system, the total energies for five possible structures, i.e., A15, D09, D019, L12, and L60, with a stoichiometry of RuPd3 were calculated as a function of lattice constants, based on the Vienna Ab Initio Simulation Package (VASP). The calculation results predicted that the D019, L12, and L60 ...
The chemical structure and bonding of the hypermetallic Al5C and Al5C- species have been studied by photoelectron spectroscopy and ab initio calculations.
Examples of transition metal complexes containing dihydrogen ligands are investigated using ab initio electronic structure calculations employing effective core potentials. Calculated geometrical structures and relative energies of various forms of WL(sub...
... goals of this program have been to develop new, more effective methods for performing accurate ab initio electronic structure calculations and to ...
Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches.
NASA Technical Reports Server (NTRS)
We have carried out extensive high quality ab initio electronic structure calculations of the ground
The equilibrium structure, dipole moment, harmonic vibrational frequencies, and infrared intensities
... the potential energy surface provided by modern electronic structure ... screening approach, to determine the equilibrium geometry and composition ...
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 ...
We present and discuss the results of the large scale Hartree-Fock calculations of Nb impurities substituting for Ti ions in SrTiO3 using ab initio computer code CRYSTAL and several supercells containing up to 135 atoms. The local structure optimisation, the electronic charge redistribution, chemical bond covalence ...
We present a unifying theory for the observed complex structures of sp-bonded elements under pressure on the basis of nearly free electron picture. In the intermediate pressure regime, the dominant contribution to crystal structure arises from Fermi-surface Brillouin zone interactions�structures which allow this ...
Quantum mechanical-based (or ab initio) methods are used to predict the stability properties of materials although their application is limited to relatively simple systems in terms of structures and number of alloy components. However thermodynamics of c...
We have carried out ab initio electronic structure calculations of the spin-orbit and rotation-orbit
Ab initio quantum chemical techniques are used to investigate covalently-bonded and hydrogen-bonded species that may be important intermediates in the reaction of hydroxyl and hydroperoxyl radicals. Stable structures of both types are identified. Basis se...
General procedures for computing alloy phase equilibria from ab initio electronic structure calculations are reviewed and applied to the Al-Li phase diagram. Free energies were calculated by the cluster variation method (CVM) in the tetrahedron approximat...
We report studies based on a combination of ab initio electronic structure and Monte Carlo (MC) technique on the problem of cation partitioning among inequivalent octahedral sites, M1 and M2 in mixed olivines containing Mg2+ and Fe2+ ions. Our MC scheme uses interactions derived out of ab ...
A global search for possible LiF cluster structures is performed up to (LiF)(8). The method is based on simulated annealing, where all the energies are evaluated on the ab initio level. In addition, the threshold algorithm is employed to determine the energy barriers for the transitions among these structures, for ...
Structural and thermal properties of small lithium clusters are studied using ab initio-based Monte Carlo simulations. The ab initio scheme uses a Hartree-Fock/density functional treatment of the electronic structure combined with a jump-walking Monte Car...
We present the results of ab initio calculations of several intrinsic and oxygen-containing defects in CaF2 including an F center, a substitutional O- ion, an O2--vacancy dipole, and FA(O2-) and F2A+(O2-) centers. The calculations have been performed using a hybrid density functional and an embedded cluster method. The calculated optical absorption (OA) ...
Atom-surface potentials entering the calculations of fast atom scattering at surfaces are often taken to be purely repulsive and parameterized by variants of the ZBL potential. However, such surface potentials derived from pairwise superpositions of binary potentials fail to reproduce recent rainbow scattering measurements performed for various atomic projectiles above different faces of ...
Molybdenum's and tantalum's high strength and high-temperature stability makes these refractory metals very attractive for use in advanced process technologies; however, the pure metals are very brittle. To describe plastic deformation requires knowledge of how dislocations--the defects responsible for crystal plasticity--evolve under stress. A classical potential for ...
The first XUV and x-ray spectra were recorded from TEXT with a grazing-incidence grating spectrograph and new crystal spectrographs. Time and space-integrated data yielded a qualitative description of the plasma. Line radiation from O, Cr, Fe, and Ni ions were recorded and identified with the aid of ab initio atomic ...
local embrittlement and crack advance. This process is known as delayed hydride cracking(DHC) [1 to qualitatively different DHC models. In titanium and zirconium alloys the stable hydride is the ffi �phase with ab initio computer simulations. In DHC both growth and elastic behaviours are important, so
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 and the predictions of ...
Approach for interpretation of nuclear magnetic resonance (NMR) spectra in magnetic materials is presented, consisting in employing the anisotropy of hyperfine interaction. The anisotropic parts of hyperfine magnetic fields on (57)Fe nuclei are calculated ab initio for a model example of lithium ferrite and utilized to assign the experimental NMR spectral ...
The X-ray crystal structure of the previously unknown bacteriophage P22 lysozyme, the product of gene 19, has been determined ab initio by direct methods using the program SIR2002. The presence of several partially occupied iodine anions and samarium cations augmented the ability of direct methods to locate all ...
We present an algorithm for calculating the conformational thermodynamics of large, flexible molecules that combines ab initio electronic structure theory calculations with a torsional path integral Monte Carlo (TPIMC) simulation. The new algorithm overcomes the previous limitations of the TPIMC method by including the thermodynamic ...
SnO2: BULK AND SURFACE SIMULATIONS BY AN AB INITIO NUMERICAL LOCAL ORBITALS METHOD A.V. POSTNIKOVa structure of ideal bulk SnO2 is well studied by ab initio calculations (Peltzer y Blanc�a, Svane study of several SnO2 surfaces, com- paring their energies of formation, and started to look
The nuclear magnetic resonance chemical shift is one of the most powerful properties available for structure determination at the molecular level. A review of advances made in the ab initio calculation of chemical shielding during the past five years is presented. Specifically, progress in the areas including the effects of an unpaired ...
There has been a significant progress in ab initio approaches to the structure of light nuclei. Starting from realistic two- and three-nucleon interactions the ab initio no-core shell model (NCSM) predicts low-lying levels in p-shell nuclei. It is a chall...
The developments of nonlinear optical (NLO) crystals in the last decade are reviewed from two aspects. In the theoretical part, on the ab initio plane-wave pseudopotential energy method, calculation of the optical responses, including the second harmonic generation coefficients, a computer-program package, and a real-space atom-cutting ...
... system organized around a common data structure. ... molecular structures; optimize structures using molecul ... ab initio quantum chemical tech- niques ...
Development of structural order in liquid aluminum upon rapid cooling is studied by ab initio molecular-dynamics simulations and the recently developed atomistic cluster alignment method. We show that there is a strong competition between icosahedral and fcc short-range orders (SROs) in the system. Although the liquid eventually ...
Since the first prediction of an atomic metallic phase of hydrogen by Wigner and Huntington over 75 years ago, there have been many theoretical efforts aimed at determining the crystal structures of the zero-temperature phases. We present results from ab initio random structure searching with ...
Completely self-consistent ab initio calculations of scattering of electrons between the lowest minima of the conduction band by short-wavelength phonons are performed for the first time for a group of А III В V semiconductor crystals. The structure constants, electron and vibrational spectra, ...
The timely integration of crystal structure databases, such as CRYSTMET, ICSD etc., with quantum software, like VASP, OresteS, ElectrA etc., allows ab initio cell and structure optimization on existing pure-phase compounds to be performed seamlessly with just a few mouse clicks. Application to ...
... Energetic polymers, Oxetanes, Quantum Chemical calculations, Configuration ... MRD/CI), Energetic compounds, Ab-initio potential functions, Crystal ...
... 10 shows that the bond angles are also predicted more accurately for Cl20 than those of the other crystals in this study. We observe angle errors ...
Ab initio density functional theory (DFT) calculations have been performed to examine various factors which may influence the ideal strength, namely multiaxial loading condition and structure with low symmetry. First, the effect of normal stress on the ideal shear strength (ISS) in covalent crystals, Si, C, Ge and ...
The goal of this research is to provide increased understanding of the chemistry and reactivity of pentavalent phosphorus compounds by analysis of structures and electronic structures obtained from ab initio molecular orbital calculations. Electronic stru...
Crystal structure prediction from first principles is still one of the most challenging and interesting issue in condensed matter science. we explored the potential energy surface of NaBH4 by a combined ab-initio approach, based on global structure optimizations and quantum chemistry. In particular, we used ...
Recently it has become possible for the first time to directly observe dislocation kink motion by electron microscopy. The method is discussed in which ab initio quantum molecular dynamics calculations in combination with these images have deepened the understanding of the atomic processes involved in both ductility and fracture in ...
As dislocation motion is resisted by the Peierls barrier, cracks in brittle crystals can be lattice-trapped. The discrete lattice structure of a crystal under loading reflects this behavior of the defect's motion. By determining the energy barrier to crack motion at loads within the range of lattice trapping, the authors are ...
The band structure of tetraza porphin nickel(II) is investigated using semiempirical crystal orbital (CO) calculations for transition metal systems that are based on the INDO approximation. The model Hamiltonian is designed to reproduce the results of ab initio calculations of double-zeta quality at low ...
From the experimental crystal structure and ab initio calculations on resveratrol and its derivatives, structural features of mechanistic importance are described. The molecular structure reveals the relative coplanarity of the trans-stilbene skeleton, and the molecular ...
Conformational characteristics, solution (melt) properties, and thermal properties of polyselenoethers [-(CH2)ySe-]x ( y=1, 2, and 3) have been revealed by the rotational isomeric state analysis of ab initio molecular orbital calculations and (1)H and (13)C NMR experiments for monomeric model compounds and compared with those of typical polyethers and ...
Following a brief review of the past work published on the structural and mechanical properties of the ? -SiAlON crystal, an ab initio computational method is outlined, which was employed to investigate the material properties and electronic structure of the ?-Si6?zAlzOzN8?z , where z=0-5 , ...
Analysis of crystal structures from the Cambridge Structural Database (CSD) that involve close contact between water and aryl rings revealed the existance of conformations where the water molecule or one of its O-H bonds is parallel to the aromatic ring plane at distances typical for stacking interactions; attractive interaction ...
We present an ab initio calculation of the structural and electronic properties of Si in a novel hexagonal, fourfold coordinated structure with 40 atoms per unit cell, obtained from the coalescence of small fullerenic cages. Hex-Si40 has a tubular structure, inducing confined electronic states ...
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 ...
The crystal structure of GPB zones in Al-Cu-Mg alloys is very unique, consisting of agglomeration of 1D crystals. Current work identifies and fully describes a new type of 1D crystal of the GPB zone family based on high-resolution STEM observations. The observation enables to generalize the ...
The first semiconductor which is studied with these techniques is the archetypal elemental semiconductor, silicon. This thesis presents the first extensive study of point defects on Si(100). The author identifies the principal defects and two primary mechanisms responsible for their dominance. The author addresses materials issues associated with the identification of the lowest energy surfaces of ...
Dec 8, 2009 ... We examine different molecular structures of nitrogen based on recent observations for analog systems. A structure with Immm symmetry and ...
NASA Website
To ab initio simulate an ionic crystal using a cluster of atoms, one must surround that cluster with point charges. These point charges add the effect of the electrostatic potential of the rest of the crystal on the electronic structure of the quantum cluster. The value of the point charges has ...
Predicting the stable crystal structures of alloys from their components is a major challenge of current materials research. Ab initio methods explore the phase stability landscape of binary alloys by calculating the formation enthalpies of a large number of structures, and identifying the ...
Magnetic susceptibility of RNi5 single crystals (R=Gd, Tb, Dy) was studied under uniform and uniaxial pressures at temperatures above TC. The uniform pressure derivatives of the paramagnetic Curie temperature ? and the crystalline electric field parameter B02 appear to be small. On the other hand, ? and B02 parameters display a large sensitivity to the uniaxial pressure due to ...
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 ...
The ideal shear strength of transition metal carbides and nitrides is calculated with the use of the ab initio pseudopotential density functional method. The microscopic mechanism that limits the ideal strength is studied using full atomic and structural relaxation and the results of electronic structure ...
Nonlocal response of the surface to the incident light is included into an ab initio one-step photoemission theory. Surface-state normal emission spectra from Be(0001) and Al(100) are calculated by a full-potential scattering method and are found to agree well with the experiment in a wide energy range. The total exciting field is obtained within the ...
For most inorganic solids, very few dense polymorphs and no low-density polymorphs are observed. Taking a wide range of tetrahedrally-coordinated binary solids (e.g., ZnO, GaN) as a prototypical system, we show that the apparent scarcity of low- density polymorphs is not due to significant structural or energetic limitations. Using databases of periodic networks as sources of ...
An unusual anisotropy of thermopower and magnetothermopower has been observed in the powerful thermoelectric Ca3Co4O9+? single crystal. The in-plane thermopower is about twice as big as the out-of-plane thermopower. Combining ab initio band structure calculation with semiclassical model analysis, we understand this ...
We study from first-principles Ca2MgSi2O7 �kermanite within the local density approximation (LDA) of the density-functional theory. The electronic band structure is formed by weakly dispersive bands, with a 4.2 eV LDA gap. We report the crystal structure, dielectric properties and we compare them with the available experimental data. ...
The crystal structure of N-(3,9-dimethyl-4-phenyl-2,5-dioxo-3,4-dihydro-2H,5H-pyrano[3,2-c]chromen-3-yl)-N-methylbenzamide methanol monosolvate, C28H23NO5�CH3OH, has been determined at room temperature by X-ray diffraction. Structural ...
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 ...
We applied ab initio total-energy calculation to study the electronic structure of Bi2Fe4O9 and Bi2Mn4O10 single crystals. Both crystals are orthorhombic with the centro-symmetric structure and belong to the mullite-type material. Most of bismuth-based oxides exhibit good ...
Fourier transform polarized IR and Raman spectra of bis(guanidine) zirconium bis(nitrilotriacetate) hydrate single crystal [C(NH(2))(3)](2)[Zr[N(CH(2)COO)(3)](2)](H(2)O) have been measured in the regions 30-4000 and 80-4000 cm(-1) and correlated with X-ray structural data. The factor group analysis has been applied in the discussion of the dichroic ...
In order to test the vibration-transit (V-T) theory of liquid dynamics, ab initio density functional theory (DFT) calculations of thermodynamic properties of Na and Cu are performed and compared with experimental data. The calculations are done for the crystal at T=0 and Tm , and for the liquid at Tm . The key theoretical ...
We report elastic constant calculation and a "theoretical" tensile experiment on stoichiometric hydroxyapatite (HAP) crystal using an ab initio technique. These results compare favorably with a variety of measured data. Theoretical tensile experiments are performed on the orthorhombic cell of HAP for both uniaxial and biaxial loading. ...
The following topics are contained in this volume: how can materials theory benefit from supercomputers and vice-versa; the materials of xerography; relationship between ab initio and semiempirical theories of electronic structure and renormalization group and the statistical mechanics of polymer systems; ab ...
We study the pressure-induced phase transition in the 2H-SiC (wurtzite) using a constant-pressure ab initio technique. A first-order phase transition from the wurtzite structure to a rocksalt structure at 600.0-700.0GPa is predicted in the constant-pressure simulations. The transformation consists of two ...
The molecular and crystal structures of the title compound have been determined from a single crystal neutron diffraction experiment at 100 K. A comparison between the main geometrical features and related properties of the in-crystal and the ab initio optimized free ...
Modern compound prediction methods can efficiently screen large numbers of crystal structure phases and direct the experimental search for new materials. One of the most challenging problems in alloy theory is the identification of stable phases with a never seen prototype; such predictions do not always follow rational strategies. While performing ...
The rhombohedral unit cells of ?-boron crystals and of hypothetical ?-boron quasicrystals were investigated by applying ab initio quantum-chemical methods. The atomic decorations of such unit cells are generally based on a suitable arrangement of eight boron icosahedra, and thus the mechanism of their cohesion was simulated by relaxing ...
Results of ab initio calculations of structural, electronic, optical, and elastic properties of pure and Yb-doped InP at pressures between ambient and 10 GPa in the density functional theory framework, using the CASTEP module of Materials Studio 4.0, are reported. It is assumed (in agreement with the experiment) that in this range of ...
Based on ab initio density functional calculations, we have investigated the validity of the recently proposed ``intermediate site/bond-centered charge ordering'' in insulating magnetite, Fe3O4. It is found that, although the Fe\\text{B2+/Fe\\text{B3+ bond dimerization along the monoclinic b direction leads to local electric dipole moments, the latter are ...
... goals of this program have been to develop new, more effective methods for perform in accurate ab initio electronic structure calculations and to ...
... Abstract : The objectives of this work which were fulfilled were to (1) use high level ab initio molecular orbital theory to predict the structures and ...
... known GAMESS suite of computer codes [2]. Accurate ab initio methods pro- ... to the systematic improvement of standard quantum-chemical methods ...
... This allowed her to gain insight into SiGe alloy superlattice structures, etching of Si by fluorine, the rate limiting chemical vapor deposition process ...
Research progress on an alternative method to ab initio variational and perturbative approaches for the electronic structure of molecules is described. Progress in the report year on the evaluation of (1) molecular properties, (2) energy derivatives with ...
In the present work we shall discuss recent advances in quantum chemical methodology that have improved the reliability of ab initio electronic structure ...
Results are reported from SDCI and CPF ab initio computations for the ground and low-lying states of
... substantial impact; these tools are now incorporated in many ab initio codes ... Most commonly used quantum chemical methods possess one or the ...
on "Quantum Chemical Calculation of the Equilibrium Structures of Small ... based on the application of ab initio quantum mechanical approaches. This ...
... profiles and three-dimensional quantitative structure-activity relationship pharmacophores using ab initio quantum chemical and pharmacophore ...
(either ab initio methods or basis sets) for electronic structure calculations, and a graph theory procedure for identifying instantaneous molecular fragment identities...
Science.gov Websites
... softening of Al-based fcc alloys using ab initio Korringa-Kohn-Rostoker augmented-spherical-wave electronic structure calculations is discussed. ...
... Beta-(1-methyl-2-pyridinium) - alpha-cyano-4-styryldicyanomethanide was optimized using semi-empirical and ab initio quantum chemical methods ...
... previous grant period have been to develop new, more effective methods for performing accurate ab initio electronic structure calculations and to ...
... progress is reported in development of ab initio computational methods for the electronic structures of molecules employing atomic spectral-product ...
... calculations have been performed on the weakly bonded CO-02 complex at the ... In the T-shaped structure, the oxygen is very weakly bonded to the ...
... optimized. Then, with the C4 C6 twist angle still constrained to 00, ... structure on the rotational pathway, yielding a rotational barrier ...
For some simple, but nontrivial molecular systems, the interaction potentials are now well determined from ab initio electronic structure calculations ...
... a transition metal, A is mostly a IIIA or IVA element of periodic table, and X ... the M2AlC formula to address the influence of the M elements (Y, Zr ...
... More recently, extensive calculations on the nitrogen oxides were conducted employing the density functional method (ref 2) in conjunction with a ...
The reaction of some organophosphorus compounds with cholinesterase is thought to proceed by nucleophilic substitution through a pentacoordinate trigonal bypyramidal structure. Recently, Robert Holmes suggested that a hexacoordinate species might be invol...
... The structures of the entrance channel transition states show the four-body intermediates ... Campus Box 427 Boulder, CO 80309-0427 ...
... Abstract : Electronic structure calculations using theoretical methods based on the linked-diagram theorem are reported for a series of dissociation ...
Mar 1, 2011 ... Conformational Characteristics of Poly(tetrafluoroethylene) (PTFE) Based Upon Ab Initio Electronic Structure Calculations on Model Molecules ...
In this work we discuss the summation of the Parquet class of diagrams within Green�s function theory as a possible framework for ab initio nuclear structure calculations. The theory is presented and some numerical details are discussed, in particular the approximations employed. We apply the Parquet method to a simple model, and ...
In this work, we present a study on water acetonitrile (AN) mixtures by molecular dynamics ab initio and X-ray diffraction techniques. Comparison of the experimental total G(r) functions of the mixtures with the results of molecular dynamics simulation shows an overall good agreement. The properties of hydrogen bonded clusters (water clusters, and water AN ...
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 ...
We report on ab initio calculations of the two-dimensional systems MoS2 and NbSe2 , which recently were synthesized. We find that two-dimensional MoS2 is a semiconductor with a gap which is rather close to that of the three-dimensional analog, and that NbSe2 is a metal, which is similar to the three-dimensional analog of this compound. We further ...
Certain classes of temperature-composition binary alloy phase diagrams can now be computed in an ab-initio'' approach. No adjustable or experimentally fitted parameter is used. The expectation value of the energy is expressed in terms of an expansion of cluster probabilities, where the prefactors, the Effective Cluster Interaction, are related to the alloy electronic ...
Certain classes of temperature-composition binary alloy phase diagrams can now be computed in an ``ab-initio`` approach. No adjustable or experimentally fitted parameter is used. The expectation value of the energy is expressed in terms of an expansion of cluster probabilities, where the prefactors, the Effective Cluster Interaction, are related to the alloy electronic ...
Zinc crystallizes in the hcp structure, but with an anomalously large c/a ratio, indicating a strong distortion away from ideal packing. Coupled cluster calculations within the framework of the method of increments, improved by an embedding scheme for metals, were performed to explore the potential energy surface of zinc with respect to the hexagonal ...
Based on the polarization-sensitive terahertz time-domain spectroscopy, we measured the birefringence for Al?O? and LiNbO? single crystals, which correspond to trigonal structures that have an uniaxial birefringence, in the THz frequency range of 0.25 to 1.4 THz. For more comprehensive understanding of the THz birefringence, the measured birefringence is ...
We propose a general model, based on Anderson superexchange and the pseudo Jahn-Teller effect, to explain why ferroelectric and octahedral tilting distortions are favored by ferromagnetic ordering when compared to antiferromagnetic tilting distortions in ABX3 (A = alkali, alkaline-earth ion, f-filling rare earth; B = magnetic transition-metal ion; X = O2-, F-) perovskite ...
Ab-initio calculations based on density functional theory have been employed to study electronic properties of Cr doped Bi4Ge3O12 (BGO), as well as its optical absorption spectra in ultraviolet region. Two different situations have been analyzed: when the Cr is situated at the Ge position (Cr4+), and when it resides at the Bi site (Cr3+). For each case the band ...
We present results from ab-initio electronic-structure calculations of mechanical properties of the rhombohedral phase of vanadium reported in recent experiments (R Ia), and other predicted high-pressure phases (R Ib and bcc), focusing on properties relevant to dynamic experiments. We find that of the three transitions the largest volume collapse (1.3%) is ...
The influence of pressure on the structural, elastic, thermal and bonding properties of four perovskite-type oxides AMO3 is studied from the point of view of the quantum theory of atoms in molecules. Ab initio investigations are performed by means of the full-potential linear augmented plane-wave method as implemented in the wien2k ...
Quantum mechanical-based (or ab initio) methods are used to predict the stability properties of materials although their application is limited to relatively simple systems in terms of structures and number of alloy components. However thermodynamics of complex multi-component alloys requires a more versatile approach afforded within ...
Research completed during the period 1 Feb. 1990 - 28 Feb. 1994 is summarized in the following included papers: 'Ab Initio Statistical Mechanics of Structural Phase Transition'; 'Ab Initio Molecular Dynamics: Analytically Continued Energy Functionals and Insights into Iterative Solutions'; ...
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 ...
Beryllium is one of the candidate materials of the neutron multiplier in the tritium-breeding blanket. Titanium beryllides such as Be12Ti are known to have advantages over beryllium from the perspectives of higher melting point, lower chemical reactivity, lower swelling and so forth. The reaction of titanium beryllides with water vapor was investigated. The sample disks of Be12Ti were exposed to ...
Isotropic 13C chemical shifts of the ribose sugar in model RNA nucleosides are calculated using SCF and DFT-GIAO ab initio methods for different combinations of ribose sugar pucker, exocyclic torsion angle, and glycosidic torsion angle. Idealized conformations were obtained using structures that were fully optimized by ...
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 ...
We present an ab initio study of the electric field gradient at Fe nuclei in the series of (FeAl)1-xTx dilute alloys with B2-type crystal structure. The ternary additions T, of concentration x ? 0.06, from the group of 3d-type transition metals (Ti, V, Cr, Mn, Co, Ni, Cu) are considered. Lattice, local valence ...
Ca shows an interesting high-pressure phase transformation sequence, but, despite similar physical properties at high pressure and affinity in the electronic structure with its neighbors in the periodic table, no complex phase has been identified for Ca so far. We predict an incommensurate high-pressure phase of Ca from first principle calculations and describe a procedure of ...
The generalized two-dimensional Peierls-Nabarro (PN) model7 for studying interfaces is developed further, where an exact generalized stacking fault energy ?-surface obtained from ab initio calculations acts as an input function for the generalized PN model. Using the multiscale modeling techniques, which combines elastic theory with ab ...
The lowest two ab initio potential energy surfaces (PES), and the corresponding nonadiabatic couplings between them, have been obtained for the H{sub 3}{sup +} system; the molecular data are compared to those calculated with the diatomic in molecules (DIM) method. The form of the couplings is discussed in terms of the topology of the molecular ...
Structural and energetic properties of small, deceptively simple anionic clusters of lithium, Li(n)(-), n = 3-7, were determined using a combination of anion photoelectron spectroscopy and ab initio calculations. The most stable isomers of each of these anions, the ones most likely to contribute to the photoelectron spectra, were found ...
Structural and energetic properties of small, deceptively simple anionic clusters of lithium, Lin-, n = 3-7, were determined using a combination of anion photoelectron spectroscopy and ab initio calculations. The most stable isomers of each of these anions, the ones most likely to contribute to the photoelectron spectra, were found ...
The high-pressure induced phase transformation from the zinc blende to rocksalt structure in SiC has been studied by the ab initio molecular dynamics method. The simulations showed that SiC passes through a tetragonal intermediate state before transforming to a monoclinic phase at 160�GPa. The mechanism for this phase transformation ...
We present results for the static and dynamic structural properties of undercooled liquid Si, at several temperatures between 1550 K and 1100 K, obtained through orbital-free ab-initio molecular dynamics simulations. The local bond angle distributions show a modest increase in the tetrahedral order upon decreasing the temperature. We also analyze the ...
Ab initio electronic structure calculations on potassium at high pressure reveal that the orthorhombic oP8 structure, found recently in sodium, has a lower enthalpy in potassium than do other candidate crystal structures recently reported to be stable at high pressure [Y. ...
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 ...
Ab initio RHF/4-31G level molecular orbital calculations and Boltzmann factors are used to calculate the room temperature probability distribution of the O--H...O hydrogen-bond angle using a model consisting of two methanol molecules. The maximum in the distribution curve occurs at 163/sup 0/. The data available from 18 neutron diffraction studies of ...
Lithium ceramics are one class of materials being considered as tritium breeders for fusion technology,and hydrogen is known to enhance the release of tritium from lithium ceramic materials. Dissociative hydrogen chemisorption on the Li{sub 2}O surfaces of the (100), (110), and (111) planes has been investigated with ab initio Hartree-Fock calculations. ...
Forty two scientific articles detailing the results of this research are abstracted and interrelated. Nine papers deal with the optical properties of solids including; Ab Initio Calculation of Crystal Tensor, Light Scattering, Morphic Effects, Group Theor...
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 ...
We present a theoretical study of crystal and electronic structures of CaB6 within a screened-exchange local density approximation (sX-LDA). Our ab initio total energy calculations show that CaB6 is a semiconductor with a gap of >1.2 eV, in agreement with recent experimental observations. We show a very ...
Ideal shear strength under superimposed normal stress of cubic covalent crystals (C, Si, Ge, and SiC) is evaluated by ab initio density functional theory calculation. Shear directions in [[Formula: see text
Based on ab initio pseudopotential calculations, the results of investigations of the lattice dynamics of silver halides AgHal (Hal = Cl, Br, I) are presented. Equilibrium lattice parameters, phonon spectra, frequency densities and effective atomic-charge values are obtained for all types of crystals under study.
The rotational mechanism of the NH{sub 4}{sup +} ion in water is analyzed by using both semiempirical (AM1) and ab initio (6-31G* SCF level) methods. AM1 predicts rapid rotation at any degree of first solvent shell hydration from n = 1-6. These results are considered artifactual since AM1 favors ion-water structures of a type not found ...
Influence of impurity Ni2+ ions on optical absorption spectra of layered CdI2 single crystals has been considered for localized level of doping. Optical properties of CdI2:Ni2+ crystals were modeled using two independent approaches: (i) DFT-based ab initio calculations and (ii) semi-empirical ...
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 ...
The computational design and prediction of materials' properties is a goal on which much progress has been made. However, it is generally necessary to first determine a material's crystal structure, and this remains a difficult problem. Previously, genetic algorithms have been successful in searching for stable crystal ...
We have investigated the electronic structure of TTF-TCNQ under uniaxial compression with ab initio plane-wave pseudopotential calculations within the local-density approximation and generalized gradient approximation. Depending on the compression direction, the constituent molecules are deformed in different ways. Along with these ...
An ab initio quantum-chemical study has been made of the possible existence in terms of structural and thermodynamic stabilities of the pentacoordinated nitrogen hydrides and fluorides, NF(n)H(5-n) for n=0 to 5. Three structurally stable species have been...
A symmetry-general approach for the least-squares, therefore precise, extraction of elastic coefficients for strained materials is reported. It analyzes stresses calculated ab initio for properly selected strains. The problem, its implementation, and its solution strategy all differ radically from a previous energy-strain approach that we published last ...
The elastic moduli of magnesium (Mg) have been evaluated as functions of pressure and temperature through the use of fluctuation formulas and Monte Carlo simulation. The simulations employ {ital ab initio} interatomic potentials for Mg derived from generalized pseudopotential theory and used previously to predict the temperature-pressure phase diagram of ...
The VOH and VOD centers in MgO, CaO, and SrO have been investigated at the ab initio quantum-mechanical level, by using the CRYSTAL98 periodic program, the Hartree-Fock Hamiltonian, the supercell scheme, and a localized basis set. The defects, formally obtained by substituting a hydrogen atom for a cation, exhibit a large relaxation of ...
It is now possible to calculate the ab initio quantum mechanics of very large biological molecules. Two things lead to this perspective, namely, (i) the advances of parallel supercomputers, and (ii) the discovery of a quantum formalism called quantum crystallography and the use of quantum kernels, a method that is well suited for parallel computation. The ...
An ab initio calculation is performed to predict the structures, lattice constants, and cohesive energies of the metastable Cu75Mo25, Cu50Mo50, and Cu25Mo75 phases. With the aid of an ab initio calculation, an n-body Cu-Mo potential is derived and proven to be realistic in reproducing some ...
The chemical control of magnetic and conduction properties for organic radicals is mainly based on t, the resonance integral, and U, the on-site repulsion, used in the Hubbard model. A qualitative analysis based on the competition between the kinetic and the Coulomb contribution, and the expression of the magnetic exchange coupling suggests that U should be roughly 800 cm(-1) while the resonance ...
For the three complex crystal structures of HIV-1 aspartic protease (an enzyme of AIDS) with its inhibitor in the Protein Data Bank, molecular dynamics of the generalized Born surface area and the ab initio fragment molecular orbital of an ABINIT-MP calculation was performed to obtain the binding free energy, the ...
According to our ab initio calculations, the recently reported undamped plasmon in compressed fcc lithium emerges not only due to the fact that the dielectric matrix determinant vanishes at long wavelengths at the plasmon energy, i.e., satisfying the ideal condition for an undamped plasmon in a crystal but also extends at large momenta ...
A detailed description, at the atomistic scale, of the dynamics of excess electrons and holes is fundamental in order to improve the performance of many optoelectronic devices. Among all recombination processes, nonradiative decay paths play a fundamental role in most semiconductor devices, such as optoelectronic devices and solar cells, limiting their efficiency. In this work, a precise ...
It has recently been suggested that a significant amount of Xe can be absorbed in ?-quartz and that this might be a significant process in the recycling of Xe from the atmosphere to the interior of the Earth. This suggestion is tested by ab initio calculations of Xe in ?-quartz using DFT. Three distinct candidate sites for Xe absorption are ...
Deuterium isotope effects measure the change in chemical shift on substitution of a proton by deuterium. They have been calculated by direct treatment of the H/D nuclear quantum effect using a multicomponent ab initio molecular orbital method based on a non-Born-Oppenheimer approximation. This method enables the determination of both the electronic and the ...
