... Title : Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. ...
DTIC Science & Technology
... from federally funded research, testing and training ... agencies for Research Development Test and Evaluation ... Title : New AB Initio Based Density ...
... Title : A Comparative Study of Nonlocal Density Functional Theory and ab initio Methods: The Potential Energy Surface of sym-Triazine Reactions. ...
The adsorption energies of methane and ethane in zeolites are investigated with ab initio molecular orbital theory and density functional theory. In this work we have used zeolite cluster models containing two, three, and five tetrahedral (Si, Al) atoms a...
National Technical Information Service (NTIS)
... atoms in fullerene and diamond nanocrystallite, respectively, are proposed and examined with ab-initio local density functional method for possible . ...
NASA Website
... nanotubes. We performed ab-initio density functional calculations and studied the optical properties of aligned SWNTs that form carbon nanotube ...
respectively, are proposed and examined with ab-initio local density functional method for possible applications as single quantum bits (qubits) in ...
... including superlattice, nanoparticles, and piezoelectric oxide supported metal. To perform this research, we will use ab-initio density functional ...
... More recently, extensive calculations on the nitrogen oxides were conducted employing the density functional method (ref 2) in conjunction with a ...
Mar 1, 2011 ... respectively, are proposed and examined with ab-initio local density functional method for possible applications as single quantum bits ...
My efforts in the Density Functional Theory (DFT) project of Dr. Bartlett's research group have been limited to the implementation of analytical energy gradients with respect to nuclear displacement in ACES2. The most immediate benefit of this work is ana...
Density Functional Theory (DFT) is one of the most used {\\em ab initio} theoretical frameworks in materials science. It derives the ground state properties of multi-atomic ensembles directly from the computation of their one-particle density \
E-print Network
We have calculated molecular geometries and electric polarizabilities for small cadmium selenide clusters. Our calculations were performed with conventional ab initio and density functional theory methods and Gaussian-type basis sets especially designed for (CdSe)(n). We find that the dipole polarizability per atom ...
PubMed
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
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...
the possible existence of high mass neutron star observations favors a stiff EoS. Ab initio calculations initio calculations of the nuclear many�body problem predict a density and isospin behavior of the Eo. The predictive power of such density functionals at supra�normal densities is ...
and compression cycles is studied. Ab-initio local- spin-density functional based molecular dynamics simula- tions the Born-Oppenheimer Local-Spin-Density Functional Molecular-Dynamics (BO-LSD-MD) method [28] in inves confining the electrons in the wire is short-ranged (as also found in recent ...
Geometry optimizations and normal-mode analyses of three conformers of 1,3,5-trinitro-s-triazine (RDX) are performed using second-order Moller-Plesset (MP2) and nonlocal density functional theory (DFT) methods. The density function used in this study is B...
The framework of ab initio density-functional theory (DFT) has been introduced as a way to provide a seamless connection between the Kohn-Sham (KS) formulation of DFT and wave-function based ab initio approaches [R. J. Bartlett, I. Grabowski, S. Hirata, and S. Ivanov, J. Chem. Phys. 122, 034104 ...
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 ...
NASA Astrophysics Data System (ADS)
We studied the optical properties of aligned carbon nanotube mats for photonic device applications. We employed ab-initio density functional calculations in the linear combination of atomic orbital formalism. The calculated dielectric functions of the sem...
Inelastic neutron scattering, density functional theory, ab initio molecular dynamics, and classical molecular dynamics were used to examine the behavior of nanoconfined water in palygorskite and sepiolite. These complementary methods provide a strong bas...
Presented here are results of ab initio Density Functional Theory (DFT) structural relaxations performed on dehydrogenated and monohydrogenated nanocrystalline diamond structures of octahedral (111) and cuboctahedral morphologies, up to approximately 2nm ...
The oxidation of the trichlorooxyphosphorus anion (POCl3(-)), which takes place in combustion flames, has been examined experimentally at a variety of temperatures and theoretically via ab initio and density functional methods. The reaction was examined i...
Some of the approaches toward obtaining an understanding of alloy phase stability within the context of ab initio density functional theory are discussed. Recent results of calculations, using the concentration functional theory of Gyorffy and Stocks, of ...
We discuss a recent investigation of adatom behavior on the AISb(001) surface using first-principles electronic structure methods based on the density functional theory. For Al and Sb adatoms, we find a number of novel adatom structures that differ dramat...
... The axial-axial-axial (AAA) and equitorial-equitorial-equitorial (EEE) conformers have C3v symmetry, a symmetry consistent with vapor and beta ...
The transport properties of two ferrocenedithiolate systems with different five-member ring connections have been estimated using the nonequilibrium Green's function formalism of quantum transport and the density functional theory. The results of the calc...
A new approach for surface studies using the density functional formalism for structural determination and a first principles many-body theory for the quasiparticle surface state energies is discussed. The many-body calculation involves the evaluation of ...
Ab initio and density functional theory (DFT) methods at the HF/6-31G*, B3LYP/6-31G*, MP2/6-31G*, and MP2/TZVP levels of theory were applied to the investigation of the relative stability of six fullerene isomers of C32. Full geometry optimization of the systems was carried out and electrostatic potential ...
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 using the gradient ...
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 using the gradient ...
� � � SBOP +44 +10 786 796 EDTB -45 +16 416 432 MBPP: mixed-basis pseudopotential method CPMD: Car of this boundary using the ab initio, density functional theory based, mixed-basis pseudopotential method [39- denum and niobium. First, the ab initio mixed-basis ...
Molecular orbital calculations on the nickel pentamer cluster were carried out using ab initio methods as well as density functional methods. The molecular orbital cluster approach using effective core potentials (ECP) was used for the ab initio calculati...
. The previous ab initio results on lattices of K atoms for coordination numbers z 8, 4, and 2 are analyzed these DFT results for K into contact with a simple and physically appealing quantum-chemical model proposed conclusions are given at the end of the paper. II. THEORETICAL METHOD We have performed the ab ...
Ab-initio study of zone centre phonons in rare-earth hexaborides, MB6, has been made using self-consistent density functional method based on norm-conserving pseudo-potentials and numerical atomic orbitals as basis set. Calculated values of zone centre phonons are in fair agreement with the experimental results.
We calculate ab initio values of tight-binding parameters for the f- electron metal Ce and various phases of Si, from local-density functional one-electron Hamiltonian and overlap matrix elements. Our approach allows us to unambiguously test the validity of the common minimal basis and two-center approximations as ...
DOE Information Bridge
Ab initio and nonlocal density functional theory (DFT) calculations were performed to determine reaction mechanisms for formation of the six- membered ring C3N3Cl3 (cyanuric chloride) from the monomer, cyanogen chloride (ClCN). MP2 geometry optimizations ...
In this work we show how the ab initio determination of van der Waals coefficients within time-dependent density functional theory can be used to build efficient and accurate atomistic models that describe the long-range interactions of proteins with other proteins and of proteins with semi-conducting surfaces. The ...
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 ...
The X-NO2 rotational energy barriers of nitromethane, nitroethylene, nitrobenzene and and a group of nitramines have been computed using a density functional (LDF) procedure, using ab initio Hartree-Fock (HF)-optimized structures of the ground and rotatio...
The C6 coefficients of van der Waals interactions have been evaluated by the dynamic polarizabilities at imaginary frequencies computed by time-dependent density-functional theory using the optimized effective potentials. The C6 coefficients thus obtained agree accurately with those from the exact-exchange counterpart in ab initio ...
Two molecular charge similarity index (CSI) methods are further evaluated for practical application - one method based on a simple CNDO-type approximation to the electron density function and the other based on an ab-initio pseudo total charge density function. The test system co...
EPA Science Inventory
The electronic properties of the ionic insulator sodium nitrite (NaNO(sub 2)) have been studied using the self-consistent, ab-initio pseudopotential-density functional method. The Kohn-Sham equations of density functional theory were solved for the electr...
its optical rotation (OR) and/or its electronic circular dichroism (ECD). In practice, this requires reliable methodologies for predicting OR and ECD. The recent application of ab initio time-dependent density functional theory (TDDFT) to the calculation of transparent spectral region OR and ECD has greatly
The tunnel ionization rate under a static intense electric field is calculated for some hydrocarbon molecules, acetylene, ethylene, and benzene, employing the ab initio density-functional theory. The ionization rate is found to reflect the properties of the highest occupied molecular orbital, in agreement with the description of the ...
Energy Citations Database
Ab initio calculations have been carried out on 3-methyl indole, and the cation and neutral radicals of 3-methyl indole, using Density Functional Theory (DFT), the Becke3-Lee-Yang-Parr functional, and the 6-31G*, 6-31+G*, 3-21G*, and TZ2P basis sets. Opti...
Critical points on the potential energy surface (PES) for sym-triazine (C3N3H3) have been calculated using nonlocal density functional (NDFT) methods. The two decomposition mechanisms for sym-triazine investigated are a concerted triple dissociation of th...
The C-H bond dissociation energy of acetylene was computed by both ab initio approaches and density functional theory in a local density approximation (DFT-LDA). Structures and energies for acetylene and its dissociation products (the ethynyl and hydrogen...
In this review we present the techniques of ab initio molecular dynamics simulation improved to its current stage where the analysis of existing processes and the prediction of further chemical features and real-world processes are feasible. For this reason we describe the relevant developments in ab initio ...
We compute the ground-state properties of finite systems of neutrons in an external harmonic trap, interacting via the Minnesota potential, using the �exact-exchange� form of orbital-dependent density functional theory. We compare our results with Hartree-Fock calculations and find very close agreement. Within the context of the interaction studied, we ...
Ab initio density functional theory (DFT) and density function perturbation theory (DFPT) have been used to investigate the thermal properties of the fcc Al3Mg and Al3Sc alloys over a wide range of pressure and temperature, in comparison with fcc Al. Phonon dispersions were ...
The adsorption energies of methane and ethane in zeolites are investigated with ab initio molecular orbital theory and density functional theory. In this work we have used zeolite cluster models containing two, three, and five tetrahedral (Si, Al) atoms and have found equilibrium structures for complexes of ...
The performance of current density functionals is analyzed in detail for the electric field gradients (EFG) of hydrogen chloride and copper chloride by comparison with ab initio methods and available experimental data. The range of density functionals applied shows good ...
A multiscale technique is developed that couples empirical molecular dynamics (MD) and ab�initio density functional theory (DFT). An overlap handshaking region between the empirical MD and ab�initio DFT regions is formulated and the interaction forces between the carbon atoms are calculated based on the ...
Misfolded metallo-proteins are potential causal agents in the onset of neuro-degenerative diseases, such as Alzheimer's and Parkinson's Diseases (PD). Experimental results involving metal chelation have shown significant promise in symptom reduction and misfolding reversal. We explore, through atomistic simulations, potential reaction pathways for the chelation of Cu^2+ from the metal binding site ...
The explicit polarization (X-Pol) method has been examined using ab initio molecular orbital theory and density functional theory. The X-Pol potential was designed to provide a novel theoretical framework for developing next-generation force fields for biomolecular simulations. Importantly, the X-Pol potential is a ...
PubMed Central
We introduce a form of density-functional theory for the ab initio description of electronic systems in contact with a molecular liquid environment. This theory rigorously joins an electron density functional for the electrons of a solute with a classical density-functional theory for the ...
We present a direct ab initio dynamics study on the kinetics of the hydrogen exchange of methane with a zeolite model. Dynamical calculations are based on the canonical variational transition state theory plus multidimensional semiclassical tunneling corrections. The reaction path information needed for rate calculations was computed by using a nonlocal ...
Ga- and As-terminated GaAs(100) surfaces are studied through first-principles density-functional pseudopotential calculations of the energies of surfaces with different stoichiometries and reconstructions. We predict structural transitions as a function of Ga and As chemical potentials within an experimentally accessible range which is shown to be fixed by the bulk energies of ...
We study the general problem of mixing for ab initio quantum mechanical problems. Guided by general mathematical principles and the underlying physics, we propose a multisecant form of Broyden�s second method for solving the self-consistent field equations of Kohn-Sham density-functional theory. The algorithm is robust, requires ...
We present ab initio density functional investigations of the atomic and electronic structure of gallium nitride nanodots and nanowires. With increasing diameter, the average Ga-N bond length in the nanostructures increases, as does the relative stability (heat of formation), approaching the values for bulk GaN. As ...
A comprehensive study of static, dynamic and electronic properties of liquid Al in a thermodynamic state near its triple point was performed by means of 205-particle ab initio molecular dynamics simulations using Kohn-Sham density-functional theory and the Langevin equation of motion. The good agreement of the results with ...
We study the effect of the splitting of neutron and proton effective masses with isospin asymmetry on the properties of the Skyrme energy density functional. We discuss the ability of the latter to predict observables of infinite matter and finite nuclei, paying particular attention to controlling the agreement with ab ...
We use ab initio density-functional calculations to study hydrogen-induced disintegration of single-wall and multiwall carbon fullerenes and nanotubes. Our results indicate that hydrogen atoms preferentially chemisorb along lines in sp2 bonded carbon nanostructures, locally weakening the carbon bonds and releasing stress. For ...
Essential oils that contain large concentrations of germacrene D are typically accompanied by cadinane sesquiterpenoids. The acid-catalyzed cyclization of germacrene D to give cadinane and selinane sesquiterpenes has been computationally investigated using both density functional (B3LYP/6-31G*) and post Hartree-Fock ...
The electronic transport properties of monolayer graphene with extreme physical deformation are studied using ab initio calculations. The aim is to explore the influence of physical bending on transport properties and identify the most important geometrical parameter. The transmission spectra are relatively insensitive to the geometrical parameters in ...
The Dzyaloshinskii-Moriya (DM) vectors arising from a fabrication induced perpendicular strain gradient in a film of bcc Fe are calculated by a combination of the ab initio density functional electron theory with a micromagnetic model. It is shown that even for large strain gradients the absolute values of the DM ...
The ab-initio calculations based on density functional theory (DFT) are performed for Fe and C in their ground state crystal structures. Heats of formation are then calculated for different Fe-C alloy compounds. The lattice constant (volume), bulk modulus and shear moduli for cementite are determined from the total energy calculations. ...
The INS spectra of several azines have been analyzed starting from force constant matrix calculated via ab initio and DFT methods. In order to reproduce both vibrational frequencies and intensities, the initial force constants must be fitted until the spectral profile is reproduced. We have checked the various ways which can be followed by the user in this ...
We regularize the potential distribution framework to calculate the excess free energy of liquid water simulated with the BLYP-D density functional. Assuming classical statistical mechanical simulations at 350 K model the liquid at 298 K, the calculated free energy is found in fair agreement with experiments, but the excess internal energy and hence also ...
Using ab initio density-functional theory, we study the role of interstitial hydrogen on the energetics of the phase transformation of iron from bcc to hcp along Bain�s pathway. The impurity creates an internal stress field that can be released through a tetragonal distortion of the lattice, promoting the bcc (ferromagnetic) ? fcc ...
Electronically nonadiabatic effects during the chemisorption of hydrogen atoms on an Al(111) surface are simulated ab initio using time-dependent density-functional theory for the electrons in combination with Ehrenfest dynamics for the nuclei. Strongly nonadiabatic effects close to the spin transition of the H atom are identified, and ...
Density functional theory based ab initio molecular dynamics simulations with explicit inclusion of empirical van der Waals (vdW) corrections of supercritical carbon dioxide have been performed. Significant changes in the intermolecular pair correlation functions of the fluid modeled with the added vdW interactions ...
The ferroelectric [001], [011], and [111] instabilities in KNbO3 with up to 12.5 mol% Cu on K or Nb sites, respectively, are investigated using both ab initio density-functional theory and classical interatomic potentials. A doping level of only about 2�4 mol% Cu on K sites enhances the ferroelectric instabilities and induces a ...
The stability of He in hcp-Ti was studied using ab initio method based on density functional theory. The results indicate that a single He atom prefers to occupy the tetrahedral site rather than the octahedral site. The interaction of He defects with Ti atoms has been used to explain the relative stabilities of He ...
The relaxation of hot hydrogen atoms upon the dissociative adsorption of H2 on Pd(100) was studied by ab initio molecular dynamics simulations based on density functional theory, modeling the full dissociative adsorption process in a consistent manner. In spite of the nonlinear dependence of every single trajectory ...
The Cytochrome P450 superfamily of enzymes are of great interest in pharmacology as they participate in an enormous range of physiological processes including drug deactivation and xenobiotic detoxification. We apply ab initio electronic structure calculations to model the interactions of the haem molecule at the P450 active site with substrate and ...
The atomic-scale processes that control the formation of carbon deposits on Ni catalysts in reforming applications are poorly understood. Ab initio Density Functional Theory calculations have been used to examine several key elementary steps in the complex network of chemical reactions that precedes carbon ...
We discuss two methods within the realm of time-dependent density functional theory to calculate frequency dependent polarizabilty of many-electron systems and use them to obtain van der Waals coefficient C6 between two such systems. One method is based on time dependent Kohn-Sham formalism and the other one is hydrodynamic approach based in terms of ...
Results are presented of a fully ab initio calculation of impact ionization rates in GaAs within the density functional theory framework, using a screened-exchange formalism and the highly precise all-electron full-potential linearized augmented plane wave method. The calculated impact ionization rates show a ...
A new �on the fly� method to perform Born-Oppenheimer ab initio molecular dynamics (AIMD) simulations is presented. Inspired by Ehrenfest dynamics in time-dependent density functional theory, the electronic orbitals are evolved by a Schr�dinger-like equation, where the orbital time derivative is multiplied by ...
Density functional theory (DFT) was examined for computing energies of temporary anions having negative electron affinities ranging from -8.0 to -0.2 eV. The calculated electron affinities are in good agreement with experiment for {pi}* states and low-energy {sigma}* states. The dependence of the DFT results on basis set was investigated. Comparisons are ...
An ab-initio molecular dynamics procedure without precalculation of the Born-Oppenheimer energy surface based on an iterative non-local density functional method employing Gaussian atomic basis has been developed. Analytical gradients are calculated and used for the propagation of nuclei. Sufficiently long trajectories can be ...
We have performed an ab initio study of the thermodynamical properties of rare-earth�magnesium intermetallic compounds MgRE (RE=Y, Dy, Pr, Tb) with B2-type structures. The calculations were carried out in the framework of density functional theory and density functional ...
Based on ab initio density-functional calculations in supercells of 3C-SiC, the stable configurations of hydrogen and dihydrogen defects have been established. The calculated formation energies are used to give semiquantitative estimates for the concentration of hydrogen in SiC after chemical vapor deposition, low temperature H-plasma ...
By using ab initio density functional theory, the structural characterizations and electronic properties of two large-diameter (13, 13) and (14, 14) armchair silicon carbide nanotube (SiCNT) bundles are investigated. Full structural optimizations show that the cross sections of these large-diameter SiCNTs in the ...
We present a combined computational and experimental study on structural and electric properties of recently synthesized heteroaromatic dyes and their simple aggregates. Ab initio and density functional theory calculations are carried out to investigate ground state and excited state properties along with their ...
Recent progress in the ab-initio molecular dynamics method and the power of parallel computing, allow the detailed study of complex chemical reaction of great industrial relevance. We illustrate this unprecedented capability by investigating the second generation Ziegler-Natta catalytic process. In this inhomogeneous catalyst, a polymerization reaction is induced by TiCl4 ...
An ab initio density functional theory-based study of the electronic band structure, the elastic, electric, elastoelectric, and linear and nonlinear optical properties of the new ion conductor LiB6O9F, has been performed. The computed band structure reveals a wide direct band gap. The coefficients of the second ...
An ab initio molecular dynamics (MD) simulation technique employing the Born-Oppenheimer approach in the framework of a Gaussian implementation of Kohn-Sham density functional theory is used to study the gas-phase conformational dynamics of an alanine dipeptide analog. It is found that conformational transformation ...
The results of ab initio calculations of the vibronically averaged components of the anisotropic magnetic hyperfine tensor in the low-lying vibronic species of the X2? electronic state of the HCCS radical are reported. The electronically averaged hyperfine coupling constants for hydrogen, deuterium, 13C and 33S are obtained as functions of two bending ...
Point defects in Fe and dilute FeCu alloys are investigated by ab initio calculations based on density functional theory. The relaxed vacancy and interstitial and substitutional Cu atom formation energies are determined as well as some migration energies. The binding energies of various Cu containing defects ...
The structural, electronic and dynamic properties of cesium chloride, ZrRu and ZrZn were studied by employing an ab initio pseudopotential method and a linear response scheme, within the generalized gradient approximation. The calculated lattice constant, bulk modulus and first-order pressure derivative of the bulk modulus were reported in B2 structure and ...
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 Carlo sampling of ...
Density functional theory is, of course, fundamentally a variational method. Therefore, in this Letter we suggest a classification of available energy density functionals into two groups, which we term (i) heuristic (H) and (ii) possibly variationally valid (PV). Quantum-chemical ab ...
A fewest switches trajectory surface hopping algorithm based on linear response time-dependent density-functional theory is developed and implemented into the plane wave ab initio molecular dynamics package CPMD. A scheme to calculate nonadiabatic couplings using a multi determinantal approximation of the excited state wave function is ...
We have investigated the adsorption of amino acid alanine on single-walled carbon nanotube using ab initio calculations based on density functional theory. Our study shows that the non-covalent interaction of alanine with nanotube depends upon the functional group nearer to the tube wall. Interaction through the ...
We have expanded the capabilities of the ab initio tight-binding molecular dynamics package FIREBALL to include calculations of optical properties. Basic zero order approximation is based on transitions between Kohn-Sham states. Corrections for electron-electron interactions are based on time dependent density ...
An electron gas-density functional approach previously used to calculate the potential between two rare gas atoms has been applied to the calculation of the interaction potential of a rare gas atom with the surface of a noble metal. The method is illustrated by calculating the repulsive potential for helium atoms interacting with copper and silver metal ...
The package fhi96md is an efficient code to perform density-functional theory total-energy calculations for materials ranging from insulators to transition metals. The package employs first-principles pseudopotentials, and a plane-wave basis-set. For exchange and correlation both the local density and generalized gradient approximations are implemented. The code has a low ...
The energetic and electronic structure of bilayered graphene (BLG) with AA stacking arrangement on a SiO2 substrate is investigated in the presence of an electric field F of different intensities by ab initio density functional calculations. The AA-stacked bilayer graphene is stable on the SiO2 substrate in the ...
Ab initio and density functional calculations have been performed to study the benzyl azide, 2-, 3- and 4-methyl benzyl azides. Several molecular properties, such as conformational equilibrium, optimal geometry, and vibrational frequencies, have been computed for these molecules. Ionisation energies were also ...
We present ab initio studies based on density functional theory within the local spin density approximation for different Ni nanocontacts and show changes in the conductance of such constrictions due to atomic rearrangements in the contact. In particular we consider an Ni particle and show that the ...
Dissociation and fission of small neutral, singly and doubly charged strontium clusters are studied by means of ab initio density functional theory methods and high-resolution time-of-flight mass spectrometry. Magic numbers for small strontium clusters possessing enhanced stability towards monomer evaporation and ...
We have measured the oxygen positions in LaNiO3 films to elucidate the coupling between epitaxial strain and oxygen octahedral rotations. The oxygen positions are determined by comparing the measured and calculated intensities of half-order Bragg peaks, arising from the octahedral rotations. Combining ab initio density-functional ...
Chances for the existence and detection of interstellar cyanovinylidene, CC(H)CN, the branched isomer of cyanoacetylene, are discussed based on the results of quantum-chemical calculations. Ab-initio (coupled cluster) and density functional theory predictions for CC(H)CN structure, electric dipole moment, rotational spectroscopy, and ...
Semiconductor nanostructures contain significant strain contributions, which in turn influence phonon properties. Model calculations for spherically shaped nanodots embedded in a host crystal are presented using the Keating model as interaction potential. It is shown that the local dot phonon density of states is to a good approximation given by the phonon density of the bulk material under ...
Two molecular charge similarity index (CSI) methods are further evaluated for practical application - one method based on a simple CNDO-type approximation to the electron density function and the other based on an ab-initio pseudo total charge density fun...
Correlated ab initio wave function calculations using MP2/aug-cc-pVTZ model chemistry have been performed for three test sets of gas phase saccharide conformations to provide reference values for their relative energies. The test sets consist of 15 conformers of alpha and beta-D-allopyranose, 15 of ...
Technology Transfer Automated Retrieval System (TEKTRAN)
We have simulated with in the Density Functional Theory (DFT) spherically cut nano-diamonds from bulk diamond at ambient conditions. The 2.6 nanometer diameter sphere is then allowed to relax at 250K and surface reconstruction is observed. Four hemispherical fullerene like regions form on the surface and while the interior maintains the diamond structure, ...
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 of ab initio ...
The new M06 functional of Truhlar and co-workers is found to be competitive with high level ab initio methods in the study of the water exchange mechanism of the [UO(2)(OH(2))(5)](2+) ion, and of the redox potentials of the aqua complexes of [AnO(2)](2+) (An = U, Np and Pu). PMID:19209355
In order to perform atomistic simulations of steel, it is necessary to have a detailed understanding of the complex interatomic interactions in transition metals and their alloys. The tight-binding approximation provides a computationally efficient, yet accurate, method to investigate such interactions. In the present work, an orthogonal tight-binding model for Fe, Mn and Cr, with the explicit ...
Theoretical Insight into the Interactions of TMA-Benzene and TMA-Pyrrole with B3LYP Density theoretical investigation of the tetramethylammonium(TMA)-benzene and TMA-pyrrole complexes has been performed density in the 5 6 aromatic system of pyrrole is larger than that in the 6 6 system of benzene
In high-pressure isentropic compression experiments (ICE), the pressure is dominated by the cold curve. In order to obtain an accurate semi-empirical cold curve for Ta, we calculate the thermal pressure from ab initio phonon and electronic excitation spectra. The cold curve is then inferred from ultrasonic and shock data. Our empirical cold pressure is ...
useful for detailed chemical kinetic modeling of aluminum combustion in HCl and chemical vapor deposition, including HCl, H2O, CO, and CO2. However, there is very little experimental information on elementary knowledge, no experiments concerning the combus- tion of Al particles in pure HCl have been reported
A SERS investigation combined with ab initio computational analysis involving Car-Parrinello molecular dynamics simulations and Density Functional Theory approach allows fundamental information to be obtained on the behaviour of thiazole in silver aqueous suspension where solvation and chemisorption processes ...
The aim of this thesis is to study metallic sodium clusters by numerical simulation. We have developed two ab initio molecular dynamics programs within the formalism of density functional theory. The first is based on the semi- classical extended Thomas-F...
By use of ab initio density-functional total-energy calculations a point defect with a negative Hubbard U is identified, for the first time, in a chalcogenide system. It is found that in c-As2Se3 two non-interacting neutral Se antisite defects are unstabl...
We investigate how the insertion of an oxygen atom in an atomically thin gold nanowire can affect its rupture. We find, using ab initio total energy density functional theory calculations, that O atoms when inserted in gold nanowires form not only stable but also very strong bonds, in such a way that they can ...
We studied the optical properties of the aligned carbon nanotube (16, 0), (10,0), and (8,4) mats for photonic device applications. We employed ab initio density functional potentials and utilized the linear combination of atomic orbital formalism. We calc...
The effect of isolated vacancies on the elastic properties of a graphene sheet has been investigated by the ab initio density functional method. An almost inverse linear dependence of the Young's modulus on the concentration of vacancies has been revealed. The height of potential barriers for the motion of ...
We present an {ital ab} {ital initio} approach for the computation of the magnetic susceptibility {chi} of insulators. The approach is applied to compute {chi} in diamond and in solid neon using density functional theory in the local density approximation, obtaining good agreement with experimental data. In solid ...
The ground-state properties of diamond are investigated using an ab initio density-functional pseudopotential scheme. The calculated equilibrium lattice constant, cohesive energy, and bulk modulus are in excellent agreement with experiment. Unlike Si and Ge, a double hump is found in the valence-electron charge density along the ...
Scanning tunneling microscopy (STM) and ab initio calculations based on density functional theory (DFT) were used to study the self-aligned silicon nanoribbons on Ag(110) with honeycomb, graphene-like structure. The silicon honeycombs structure on top of the silver substrate is clearly observed by STM, while the ...
We employ atomic first principles theory to study the properties of realistic graphene nanoelectronic systems. We focus on the role of different contact materials and their effect on the transport properties at the graphene/metal junction. The current-voltage characteristics were calculated using density functional theory (DFT) combined with ...
Equilibrium structure, local densities of states, and electronic transport in a gold nanowire made of a four atom chain supported by two gold electrodes, which has been imaged recently by high-resolution electron microscopy, and chemical modification of the wire via the adsorption of a methylthiol molecule, are investigated with ab initio local ...
First-principles density-functional calculations utilizing ab initio pseudopotentials and plane-wave expansions are used to determine lattice parameters, bulk moduli, and band structures for AlN, GaN and InN. It is found that large numbers of plane waves ...
We report ab-initio calculations of the spin-dependent transport and magnetoresistance of Ni atom wires. The electronic states are calculated using a numerical pseudo atomic orbital basis set in the frame work of the density functional theory, and the con...
Models of encapsulated 1/2 nuclear spin H-1 and P-31 atoms in fullerene and diamond nanocrystallite, respectively, are proposed and examined with ab-initio local density functional method for possible applications as single quantum bits (qubits) in solid-...
We applied the locally self-consistent multiple scattering (LSMS) method to the study Fe-based bulk amorphous metals. The LSMS method is an order- N approach to the electronic structure calculation for solid state materials based on density functional the...
genomic strands (.100 bases),3 have been found to wrap around single-walled CNTs forming tight helices. ss the experimental absorbance and LD data for DNA wrapped on CNTs are best reproduced. The directions indicated (CNTs), by combining ab initio time- dependent density functional theory and optical spectroscopy
The rotational dynamics of methyl groups in 2,6 dimethylpyrazine and in cobalt and nickel acetates have been studied by neutron scattering and a combination of ab initio and empirical calculations. These results and the precision of the method are compared to those obtained by DFT calculations in each case. It has been shown that DFT gave excellent ...
Concerted triple dissociation reactions of 1,3,5-triazacyclohexane (I) and 1,3,5-trinitro- 1,3,5-triazacyclohexane (II,RDX) were investigated byusing semiempirical, ab initio, and local density functional (LDF) methods. Gaseous phase structures and energi...
We report anisotropic collision-induced Raman scattering intensities by the Kr-Xe atomic pair recorded in a gas mixture of Kr and Xe at room temperature. We compare them to quantum-mechanical calculations on the basis of modern incremental polarizability models of either ab initio post-Hartree-Fock or density ...
We have investigated the ground state structural, electronic and optical properties of CuAlSe2 compound by using density functional theory employing three different functionals for the exchange correlation (XC) potentials. Our calculation shows that given compound is direct band gap semiconductor. We noticed that (GGA-EV) shows good agreement with the ...
Cesium iodide properties, both in the bulk and on (110) and (100) surfaces, are studied using density functional theory. The bulk lattice constant, bulk modulus, and elastic constants are in good agreement with the experimental values. The electronic band structure is also calculated, as well as the density of states. On the surfaces, relaxation of the ...
The system consisting of two diamond (001) surfaces in contact was studied by means of plane-wave/pseudopotential density functional calculations. Different hydrogen coverages, ranging from fully hydrogenation to bare surfaces, were considered. The adhesion energy was calculated as a function of both the separation and the lateral displacement of the two ...
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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...
We present Kelvin probe force microscopy measurements of single- and few-layer graphene resting on SiO2 substrates. We compare the layer thickness dependency of the measured surface potential with ab initio density functional theory calculations of the work function for substrate-doped graphene. The ...
Recently, we introduced a new density-functional theory (DFT) approach for the calculation of NMR shielding constants. First, a hybrid DFT calculation (using 5% exact exchange) is performed on the molecule to determine Kohn-Sham orbitals and their energies; second, the constants are determined as in nonhybrid DFT theory, that is, the paramagnetic contribution to the constants ...
The multiconfigurational CASSCF/CASPT2 approach, along with various functionals of density functional theory, is applied to selected iron(II)-nitrosyl ({FeNO}(7)) complexes, both with heme and nonheme groups. The energetics of the lowest doublet and quartet spin states at the correlated ab initio (CASPT2) level is ...
Ab initio density functional theory calculations are carried out in order to predict the evolution of structural materials under aggressive working conditions such as cases with exposure to corrosion and irradiation, as well as to predict and investigate the properties of functional materials for photovoltaic ...
We present in detail the formulation of the ab initio theory we have developed for the calculation of the macroscopic second-order susceptibility ?(2) . We find a general expression for ?(2) valid for any fields, containing the ab initio relation between the microscopic and macroscopic formulation of the ...
Density functional theory developed by Hohenberg, Kohn and Sham is a widely accepted, reliable ab initio method. We present a non-periodic, real space, mesh-free convex approximation scheme for Kohn�Sham density functional theory. We rewrite the original variational ...
Using ab initio density functional calculations, we study the microscopic mechanism of hydrogen release from ammonia borane (NH3BH3) and the reverse process leading to its subsequent recharging with hydrogen. Our total energy surfaces indicate the most favorable pathways to thermally convert the NH3BH3 molecular ...
Quantum chemical calculations of energies, geometrical structure and vibrational wave numbers of 3,4-dimethoxybenzonitrile (DMBN) were carried out by the ab initio Hartree-Fock (HF) and density functional theory (DFT) with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. The ...
The direct application of ab-initio methods (Hartree-Fock or density functional theory) to study complete biomolecules has been impossible due to the huge computational cost of fully quantum mechanical calculations. As an initial step towards overcoming this problem, we implemented an ab-initio-based method to ...
Properties of molecules solvated in ionic liquids (ILs) are strongly affected by solvent environment. For this reason, to give reliable results, ab initio calculations on solutes in ILs, including ions constituting ionic liquid itself, have to self-consistently account for the change of both electronic and classical solvation structure in ILs. Here, we ...
We describe large scale ab initio quantum chemical and mixed quantum mechanics/molecular mechanics (QM/MM) methods for studying enzymatic reactions. First, technical aspects of the methodology are reviewed, including the hybrid density functional theory (DFT) methods that are typically employed for the QM aspect of ...
The ab initio calculation with the density functional theory and plane-wave bases is carried out for stepped Si(111)?2�1 surfaces that were predicted in a cleavage simulation by the large-scale (order-N) electronic structure theory (T. Hoshi, Y. Iguchi and T. Fujiwara, Phys. Rev. B 72 (2005) 075323). The present ...
Ab initio and density functional theory (DFT) calculations of nuclear magnetic resonance shielding tensors in benzene-methane and two isomers of the benzene dimer are reported, with the aim of probing the changes in shielding induced by the formation of supramolecular complexes from isolated molecules. It is shown ...
A hybrid computational method intended for simulations of biomolecules in solution is described. The ab initio Kohn-Sham (KS) density functional theory (DFT) method is used to describe the chemically active part of the system and its first solvation shells, while a frozen-density orbital-free (FDOF) DFT method is ...
... This study involves: Ab-initio crystal orbitals and polymer orbitals; Ab-initio coupled cluster program; Ab-initio quantum chemical calculations and ...
Time-dependent density functional theory (TD-DFT) and correlated ab initio methods have been applied to the electronically excited states of vitamin B12 (cyanocobalamin or CNCbl). Different experimental techniques have been used to probe the excited states of CNCbl, revealing many issues that remain poorly ...
The ab initio/classical free energy perturbation (ABC-FEP) method proposed previously by Wood et al. [J. Chem. Phys. 110, 1329 (1999)] uses classical simulations to calculate solvation free energies within an empirical potential model, then applies free energy perturbation theory to determine the effect of changing the empirical solute-solvent interactions ...
We have combined the Boltzmann transport equation with an ab initio approach to compute the thermoelectric coefficients of semiconductors. Electron-phonon, ionized impurity, and electron-plasmon scattering mechanisms have been taken into account. The electronic band structure and average intervalley deformation potentials for the electron-phonon coupling ...
The constrained space orbital variation (CSOV) method for the analysis of the interaction energy has been implemented in the periodic ab initio CRYSTAL03 code. The method allows for the partition of the energy of two interacting chemical entities, represented in turn by periodic models, into contributions which account for electrostatic effects, mutual ...
Substitution of more than 33% of the naturally abundant O16 in strontium titanate SrTiO3 by O18 causes the system to become ferroelectric at low temperatures. The ferroelectricity has been observed via susceptibility measurements, but to date the details of the ferroelectric phase and the phase transition are unclear. Using ab initio ...
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 ...
We report an {ital ab initio} evaluation of the surface energy of a simple metal, performed via a coupling-constant integration over the dynamical density-response function. The rapid rate of change of the electron density at the surface is treated exactly. Long-range correlations are treated self-consistently in the random-phase approximation; short-range ...
We report plane-wave pseudo-potential ab initio calculations using density functional theory in order to investigate the structural parameters, elastic constants, bonding properties and polycrystalline parameters of copper nitrides in zincblende, rocksalt and fluorite structures. Total and partial densities of ...
We use ab initio density functional calculations to investigate the structural stability and vibrational spectra of small boron aggregates in different charge states. In search of candidates for the largest stable 2D boron aggregates, we focus on systems with one atom less than B20 clusters with confirmed 3D ...
A constant pressure ab initio MD technique and density functional theory with a generalized gradient approximation (GGA) was used to study the pressure-induced phase transition in wurtzite ZnTe. A first-order phase transition from the wurtzite structure to a Cmcm structure was successfully observed in a ...
A systematic study of ground state properties of cubic (3C) and hexagonal (6H, 4H, 2H) polytypes of normal (nonnitride) III-V compounds is reported using well-converged density-functional calculations within local density approximation, ab initio pseudopotentials, and projector-augmented wave method. Equilibrium results are obtained ...
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 quenchable and transformed to ...
Vibrational eigenfunctions are calculated on-the-fly using semiclassical methods in conjunction with ab initio density functional theory classical trajectories. Various semiclassical approximations based on the time-dependent representation of the eigenfunctions are tested on an analytical potential describing the ...
On the basis of ab initio calculations employing density functional theory (DFT) we investigate half metallic ferromagnetism in zinc-blende and wurtzite compounds composed of group I/II metals as cations and group V elements as anions. We find that the formation of ferromagentic order requires large cell volumes, ...
Spectroscopic ellipsometry is used to determine the complex refractive index (n-ik), porosity, and thickness of porous silicon (PSi) films. These films are obtained by anodizing p-type crystalline silicon in a hydrofluoric acid bath. After etching, PSi samples are heated to 750 �C in a controlled oxygen environment. A detailed analysis of the ellipsometry data is performed in order to determine ...
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 data. An analysis of ...
Molecular dynamics (MD) is a powerful tool to probe the thermodynamic and kinetic properties of solid, glass and liquid phases. In classical molecular dynamics (CMD), empirical models are used to describe the force by considering bond, bend and dihedral angle contributions with parameters fitted to experimental data or first-principles calculations of small clusters. In the ab ...
Gas-phase activation energies were calculated for three lithium enolate reactions by using several different ab initio and density functional theory (DFT) methods to determine which levels of theory generate acceptable results. The reactions included an aldol-type addition of an enolate to an aldehyde, a proton ...
Lattice dynamics and thermodynamic properties of antiferromagnetic Fe2SiO4-spinel have been studied using density functional theory. Phonon dispersions are obtained for several hydrostatic pressures up to 20 GPa. They are used to calculate thermodynamic properties within the quasiharmonic approximation. Comparison with ab ...
Lattice dynamics and thermodynamic properties of antiferromagnetic Fe(2)SiO(4)-spinel have been studied using density functional theory. Phonon dispersions are obtained for several hydrostatic pressures up to 20 GPa. They are used to calculate thermodynamic properties within the quasiharmonic approximation. Comparison with ab ...
Atomic geometries, electronic structures, and magnetic moments of several metal clusters with 13 atoms are studied by ab initio density-functional calculations. The ground state structures of 13-atom metal clusters were previously assumed to be icosahedron, cuboctahedron, or decahedron. However, in this study, using ...
Electronic structure methods based on density-functional theory, pseudopotentials, and local-orbital basis sets offer a hierarchy of techniques for modeling complex condensed-matter systems with a wide range of precisions and computational speeds. We analyze the relationships between the algorithms for atomic forces in this hierarchy of techniques, going from empirical tight-binding through ...
The static and dynamic properties of liquid Sn at two di?erent thermodynamic states have been studied from the Orbital Free Ab-Initio Molecular Dynamics (OFAIMD) simulation method. This method is based on the density functional theory (DFT) of Hohenberg and Kohn. The exchange and correlation interaction is described here with the local ...
This talk presents the result of an ab-initio study of Ruddlesden-Popper(RP) phases for Srn+1TinO3n+1(n = 1, 2, 3, ?) compounds with the density functional theory(DFT). In particular, we present results for the relation between octahedral rotations and external strains. We find that rotational reconstructions are energetically ...
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 ...
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 an ...
One of the main research efforts of the recent years has been the development of an efficient way to select desired carbon nanotubes according to their size and their electronic properties. This selectivity would allow easier fabrication of field effect transistor and light-emitting diode devices with appropriate nanotubes. An appealing approach to assess this problem is to use the dependence of ...
Ab initio calculations based on density functional theory have been performed to determine the properties of self-interstitial atoms (SIAs), vacancies, and single H and He atoms in hcp-Er. The results show that the most stable configuration for a SIA is a basal octahedral configuration, while the octahedral (O), ...
Ab initio calculations for the strongly exoergic Li2+F harpoon reaction are presented using density-functional theory, complete active space self-consistent field, and multireference configuration interaction methods to argue that this reaction would be an ideal candidate for investigation with ultracold molecules. The lowest six ...
We have employed ab initio molecular dynamics to investigate the equilibrium geometries, energetics, and the nature of bonding in mixed Li-Sn clusters. Our studies reveal that a small percentage of Sn in Li-rich clusters introduces significant changes in the equilibrium geometries. It is also seen that the geometries of Sn-rich clusters are influenced by ...
We investigate a reaction of boron trichloride (BCl3) with iron(III) hydroxide (Fe(OH)3) by ab initio quantum chemical calculation as a simple model for a reaction of iron impurities in BCl3 gas. We also examine a reaction with water. We find that compounds such as Fe(Cl)(OBCl2)2(OHBCl2) and Fe(Cl)2(OBCl2)(OHBCl2) are formed while producing HCl and ...
