Two approaches for directly computing a molecular heat of formation based on sophisticated ab initio
NASA Technical Reports Server (NTRS)
... Title : Ab Initio Calculation of Vibrational Circular Dichroism Spectra Using Accurate Post-Self-Consistent-Field Force Fields: trans-2,3 ...
DTIC Science & Technology
... goals of this program have been to develop new, more effective methods for performing accurate ab initio electronic structure calculations and to ...
Harding and Goddardl (HGI) computed accurate ab initio potential ... In order to resolve this uncertainty Harding and Goddard ...
NASA Website
We have carried out extensive high quality ab initio electronic structure calculations of the ground
... goals of this program have been to develop new, more effective methods for perform in accurate ab initio electronic structure calculations and to ...
... known GAMESS suite of computer codes [2]. Accurate ab initio methods pro- ... to the systematic improvement of standard quantum-chemical methods ...
Aug 24, 2011 ... We have performed high-level ab initio calculations of the ground state and ... can be accurately treated by quantum chemical methods. ...
... and many-body perturbation theory (MBPT) methods for the accurate inclusion of electron correlation in ab initio quantum chemical calculations of ...
... fuels requires an interdisciplinary approach involving ab initio modeling, synthesis ... value of high speed video and quantum chemical calculations to ...
... previous grant period have been to develop new, more effective methods for performing accurate ab initio electronic structure calculations and to ...
... 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 ...
Spectroscopic constants and dissociation energies for the ground states of N2, O2, and F2 determined
The ab initio calculation of harmonic force fields using post-self-consistent (post-SCF) methods has recently increased greatly in efficiency. As a result, accurate post-SCF harmonic force fields are now achievable for experimentally accessible chiral mol...
National Technical Information Service (NTIS)
A classical Lennard-Jones potential is derived from a fit to the ab initio energies obtained from an all-electron mixed-basis calculation for methane in zeolite LTA. The potential predicts the heat of adsorption, adsorption isotherm, and self-diffusivity of methane in excellent agreement with experiment. This study suggests, for the first time, that ...
PubMed
... This study involves: Ab-initio crystal orbitals and polymer orbitals; Ab-initio coupled cluster program; Ab-initio quantum chemical calculations and ...
There is reported here an accurate ab initio calculation of the fixed nuclei potential curve for the B prime singlet sigma u state of H2 together with approximate values of the adiabatic corrections to the potential curve for this state. The state is obse...
The geometries and energetics of 16 aromatic hydrocarbons are obtained from ab initio molecular orbital calculations at the 6-31G{sup *} SCF level. The energies are used to derive group equivalents that enable calculation of accurate heats of formation. Several applications of the group equivalents are described.
Energy Citations Database
Accurate quartet- and doublet-state potential-energy surfaces for the interaction of a hydrogen atom and an oxygen molecule in their ground states have been determined from an ab initio calculation using large-basis sets and the internally contracted mult...
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'; 'Ab ...
NASA Astrophysics Data System (ADS)
An accurate and efficient molecular alignment technique is presented based on first principle electronic structure calculations. This new scheme maximizes quantum similarity matrices in the relative orientation of the molecules and uses Fourier transform techniques for two purposes. First, building up the numerical representation of true ab ...
PubMed Central
Both ab initio MO--LCAO--SCF and the electron-gas (or Gordon--Kim) methods have been used to compute the intermolecular potential (Phi) of N/sub 2/ molecules for seven different N/sub 2/--N/sub 2/ orientations. The ab initio calculations were carried out using a (4s3p) contracted Gaussian basis set with and without ...
... Title : Chalcopyrite Magnetic Semiconductors: An Ab-Initio Study of Their Structural, Electronic and Magnetic Properties. ...
... from federally funded research, testing and training ... for Research Development Test and Evaluation ... COMPENDIUM OF AB INITIO CALCULATIONS ...
... Accession Number : ADA219907. Title : An Ab Initio Study of the Geometry and Rotational Barrier of 4- Phenylimidazole. ...
... from federally funded research, testing and training ... and agencies for Research Development Test and Evaluation ... Title : Ab Initio Calculations of the ...
... Title : Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. ...
... Title : AB Initio Quantum Chemical Investigations of Solubilities in Supercritical Solutions. Descriptive Note : Conference Paper,. ...
The main goals of this program have been to develop new, more effective methods for perform in accurate ab initio electronic structure calculations and to use these methods for the prediction of molecular structure, bonding and reactivity, especially for ...
The main goals of this program have been to develop new, more effective methods for performing accurate ab initio electronic structure calculations and to use these methods for the prediction of molecular structure, bonding and reactivity, especially for ...
State-of-the-art, calibrated ab initio quantum chemical calculations have been performed to obtain accurate structures, energies, and vibrational frequencies of the lowest singlet states of HNS and NSH, which are closed-shell states. Enthalpies of formati...
The possible role of electronic structure on observed phonon anomalies in high-temperature superconductivity transition-metal carbides is studied by means of accurate ab initio calculations of the conduction electron response function. From augmented-plan...
Brezina, R., W.-K. Liu, and S. Green, 1995: Close-coupling calculation of line mixing ... Using an accurate ab initio potential and converged close-coupling ...
Under AFOSR support over several years, coupled-cluster (CC) and many-body perturbation theory (MBPT) methods for the accurate inclusion of electron correlation in ab initio quantum chemical calculations of molecules have been definitively established as ...
High impact publication on innovative work to understand magnetic coupling in magnetic insulators and how to evaluate accurately the magnetic coupling constants.
The efficient development of hypergolic fuels requires an interdisciplinary approach involving ab initio modeling, synthesis, and experimental physical chemistry. Candidate molecules must exhibit hypergolic ignition delay times that are fast enough to war...
Ab initio calculations of the electronic structure of Hn- and Hn+ clusters have been carried out using accurate Gaussian basis sets and with levels of theory up to fourth-order perturbation theory (MP4) and single and double excitation configuration inter...
This final report describes the initial two phases of the overall project. In the first phase, accurate barriers and energetics were calculated for 7 reactions involved in O(3P) oxidation of hydrocarbons. This was done by MRCI/CASSCF ab initio calculation...
The requirements for very accurate ab initio quantum chemical prediction of dissociation energies are examined using a detailed investigation of the nitrogen molecule. Although agreement with experiment to within 1 kcal/mol is not achieved even with the m...
The molecular cluster model approach for the description of processes at surface is presented. It involves using finite clusters which contain surface atoms interacting with atomic or molecular adsorbates. Accurate ab initio wavefunctions can be obtained ...
The work done in this paper is based on our earlier work on developing an extended Miedema model and then using it to downselect potential alloy systems. Our approach is to closely couple the semi-empirical methodologies to more accurate ab initio methods...
We compare ab initio broad spectrum calculations of the K-edge X-ray absorption spectra of copper and molybdenum against accurate experimental measurements and tabulated standards on an absolute scale. Comparisons are also presented for the fine structure in the spectra.
The main goals in the previous grant period have been to develop new, more effective methods for performing accurate ab initio electronic structure calculations and to use these methods for the prediction of molecular structure, bonding and reactivity, es...
Early scattering experiments revealed that the proton was not a point particle but a bound state of many quarks and gluons. Deep inelastic scattering (DIS) experiments have accurately determined the probability of struck quarks carrying a fraction of the ...
Ab initio calculations have been performed at the SCF level in the STO-3G, 3-21G, and 6-31G* basis sets on a variety of benzenoid and nonbenzenoid aromatic hydrocarbons, ranging from benzene to coronene. It is shown that (1) the enthalpy changes for homodesmic reactions involving only benzenoid aromatics can be computed accurately in ...
... Title : AB Initio Study of the Electronic Magnetic Circular Dichroism ... functions are determined using as initio quantum chemical techniques including ...
We have calculated the melting temperature of tungsten by two ab initio approaches. The first approach can be divided into two steps. In the first step, we simulate a large coexisting solid and liquid system by the classical embedded-atom method potential and obtain an approximate melting temperature. In the second step, we compute the ...
We report a highly correlated multireference configuration interaction calculation of the near-equilibrium potential energy surface of ozone using a large correlation consistent basis set. Three-dimensional analytical expressions are obtained for the potential energy and dipole moment functions using least-squares fits to ab initio points near the C{sub ...
Due to recent advances in methods and computers, the accuracy of ab calculations has reached a point
The interaction potential energy surface (PES) of H{sub 4} is of great importance for quantum chemistry, as a test case for molecule--molecule interactions. It is also required for a detailed understanding of certain astrophysical processes, namely, collisional excitation and dissociation of H{sub 2} in molecular clouds, at densities too low to be accessible experimentally. ...
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 model parameters are ...
A biased potential molecular dynamics simulation approach, accelerated molecular dynamics (AMD), has been implemented in the framework of ab initio molecular dynamics for the study of chemical reactions. Using two examples, the double proton transfer reaction in formic acid dimer and the hypothetical adiabatic ring opening and subsequent rearrangement ...
Recent accurate observations [1] of collision-induced absorption (CIA) in the nitrogen and oxygen fundamentals pointed at the existence of the minimum in its integrated intensity temperature variation. This work aims at simulation of the CIA intensity in N2 using quantum chemical complete potential energy and dipole surfaces for N2-N2 system. The absolute magnitude of CIA ...
The methodology of ab initio molecular dynamics, wherein finite-temperature dynamical trajectories are generated by using forces computed "on the fly" from electronic structure calculations, has had a profound influence in modern theoretical research. Ab initio molecular dynamics allows chemical processes in ...
The methodology of ab initio molecular dynamics, wherein finite-temperature dynamical trajectories are generated by using forces computed �on the fly� from electronic structure calculations, has had a profound influence in modern theoretical research. Ab initio molecular dynamics allows chemical processes in ...
We have carried out self-consistent reaction field (SCRF) calculations on the bacteriochlorophyll (BChl) and bacteriopheophytin (BPh) molecules at the Hartree-Fock level using the ab initio electronic structure code PSGVB together with an accurate numerical Poisson-Boltzmann solver. These are by far the largest ab ...
The rotational spectrum of chlorofluoroiodomethane (CHClFI) has been investigated. Because its rotational spectrum is extremely crowded, extensive ab initio calculations were first performed in order to predict the molecular parameters. The low J transitions were measured using a pulsed-molecular-beam Fourier transform spectrometer, and the millimeter-wave ...
An efficient procedure based on the reproducing kernel Hilbert space interpolation method is presented for constructing intermolecular potential energy surfaces (PES) using not only calculated ab initio data but also a priori information on long-range interactions. Explicitly, use of the reciprocal power reproducing kernel on the semiinfinite interval ...
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 Ga, As, and GaAs. ...
We calculate equilibrium rate constants for ortho-para conversion in hydrogen and deuterium by an atomic mechanism. The calculations are based on an accurate ab initio potential surface, transition state theory, and an adiabatic transmission coefficient. The calculated rate constants are demonstrated to be reliable within 40-50%, and ...
The rates of intramolecular proton transfer are calculated on a full-dimensional reactive electronic potential energy surface that incorporates high level ab initio calculations along the reaction path and by using classical Transition State theory, Path-Integral Quantum Transition State Theory, and the Quantum Instanton approach. The specific example ...
The study and prediction of chemical reactivity is one of the most influential contributions of quantum chemistry. A central concept in the theoretical treatment of chemical reactions is the reaction pathway, which can be quite difficult to integrate accurately and efficiently. This talk will outline our developments in the integration of these pathways on ...
The quantum dynamics of the rotational quenching of the Mg24H+(X1?+) molecular cation interacting with He4(1S) as a buffer gas, at relative temperatures ranging from 1 K down to millikelvins, is described by accurate close coupling scattering calculations on an ab initio potential energy surface. The efficiency of the process is ...
High-level quantum-chemical ab initio coupled-cluster and multiconfigurational perturbation methods have been used to compute the vertical and adiabatic electron affinities of the five canonical DNA and RNA nucleobases: uracil, thymine, cytosine, adenine, and guanine. The present results aim for the accurate determination of the ...
We present a new linear scaling ab initio total energy electronic structure calculation method based on the divide-and-conquer strategy. This method is simple to implement, easily to parallelize, and produces very accurate results when compared with the direct ab initio method. The method has ...
DOE Information Bridge
Ab initio molecular orbital theory has been used to calculate accurate enthalpies of formation and adiabatic electron affinities or ionization potentials for N3, N3(-), N5(+), and N5(-) from total atomization energies. Born-Haber cycle calculations, using...
A first-principles analysis of ballistic electron emission spectroscopy (BEES) is used to extract hot-electron lifetimes in metals. The lifetimes are computed within an ab initio framework based on density-functional theory and the GW approximation, and are used in a Keldysh Green function approach for the calculation of BEES currents. For the two ...
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 ...
The interaction potential energy surface (PES) of H4 is of great importance for quantum chemistry as a test case for molecule-molecule interactions. It is also required for a detailed understanding of certain astrophysical processes, namely collisional excitation and dissociation of H2 in molecular clouds, at densities too low to be accessible experimentally. The 6101 ab ...
The potential energy surface for trimers of hydrogen fluoride is examined for multiple arrangements of the three-molecule cluster. Several established approaches to model the potential energy are examined, including a strictly pairwise additive potential, an established polarizable potential model, another, strictly three-body polarizable model, and a three-body potential recently fitted to ...
We have applied the ab initio path integral molecular dynamics simulation to study hydronium ion and its isotopes, which are the simplest systems for hydrated proton and deuteron. In this simulation, all the rotational and vibrational degrees of freedom are treated fully quantum mechanically, while the potential energies of the respective atomic ...
We report full-dimensional, ab initio potential energy (PES) and dipole moment surfaces (DMS) for water. The PES is a sum of one-, two- and three-body terms. The three-body potential is a fit, reported here, to roughly 30,000 intrinsic three-body energies obtained with second-order M�ller-Plesset perturbation theory (MP2) and using the aug-cc-pVTZ basis ...
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 ...
The potential of mean force for the dissociation of a Ca-Cl ion pair in water is calculated from ab initio molecular dynamics simulations. The constraint-force method is employed to enhance sampling over the entire range of the reaction coordinate (Ca-Cl distance) from 2.2 to 6.5 A?. Particular attention is paid to equilibration of the system as it is ...
The study of materials properties under extreme conditions has made considerable progress over the past decade due to both improvements in experimental techniques and advanced modeling methods. The availability of accurate models is crucial in order to analyze experimental results obtained in extreme conditions of pressure and temperature where experimental data can be scarce. ...
Molecular mechanics valence force field parameters for the sulfonamide group, SO[sub 2]NH, have been derived from ab initio calculations at the RHF/6-31G* level of theory. The force field parameters were designed to be used in conjunction with existing parameters from the MM2/MMP2 force field. The new parameters are demonstrated to ...
We present full-dimensional potential energy surfaces (PESs) for hydrated chloride based on the sum of ab initio (H(2)O)Cl(-), (H(2)O)(2), and (H(2)O)(3) potentials. The PESs are shown to predict minima and corresponding harmonic frequencies accurately on the basis of comparisons with previous and new ab ...
... AB-INITIO SIMULATION OF a/2110> ... 4. TITLE AND SUBTITLE AB-INITIO SIMULATION OF a/2110> SCREW DISLOCATIONS γ-TiAl 5c. ...
... ADP012740 TITLE: Ab Initio Study on Spin Polarization of III-V Compound Tips ... Ab initio study on spin polarization of III-V compound tips ...
Ab initio electronic structure methods can supplement CALPHAD in two major ways for subsequent applications to stability in complex alloys. The first one is rather immediate and concerns the direct input of ab initio energetics in CALPHAD databases. The o...
...with this part. The certificate shall be void ab initio for those vehicles causing the...issued, and the certificate may be deemed void ab initio. (C) The manufacturer...with this part. The certificate shall be void ab initio for those vehicles causing...
Code of Federal Regulations, 2010
... ADP023770. Title : ab-Initio Molecular Dynamics Simulations of Molten Ni-Based Superalloys. Descriptive Note : Conference paper. ...
... Title : Ab-Initio Molecular Dynamics Simulations of Molten Ni-Based Superalloys. Descriptive Note : Conference paper (preprint). ...
... Accession Number : ADA351780. Title : Ab Initio and DFT Potential Energy Surfaces for Cyanuric Chloride Reactions. Descriptive Note : Final rept. ...
... 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. ...
... Accession Number : ADA270577. Title : Ab Initio Potential Energy Surface for the H + OCS Reaction. Descriptive Note : Final rept. ...
... Ab initio direct trajectory simulation on hydrogen atom transfer in 7-azaindole in the electronic excited state with assist of water molecules ...
