We introduce a scheme to include many-body screening processes explicitly into a set of self-consistent equations for electronic-structure calculations using the Gutzwiller approximation. The method is illustrated by the application to a tight-binding model describing the strongly correlated ?-Ce system. With the inclusion of the 5d electrons into the ...
NASA Astrophysics Data System (ADS)
We introduce a scheme to include many-body screening process explicitly into self-consistent equations for electronic structure calculations by employing Gutzwiller approximation. The method is illustrated by applying to a tight-binding model of the strongly correlated ?-Ce. The critical Coulomb repulsion Uff^c between the 4f electrons for electronic phase ...
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...
National Technical Information Service (NTIS)
... from federally funded research, testing and training ... agencies for Research Development Test and Evaluation ... Title : New AB Initio Based Density ...
DTIC Science & Technology
Due to recent advances in methods and computers, the accuracy of ab calculations has reached a point
NASA Technical Reports Server (NTRS)
... Title : Structure of Perfluoromethanimine by Microwave, Infrared, and Raman Spectroscopy, Electron Diffraction, and ab Initio Methods,. ...
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 ab initio centroid molecular dynamics (CMD) method is developed by combining the CMD method with the ab initio molecular orbital method. The ab initio CMD method is applied to vibrational ...
... (U) DEVELOPMENT OF EFFECTIVE QUANTUM CHEMICAL METHOD FOR ... array of semiempirical approaches and ab initio calculations followed ...
In the second phase, a ultrafast semi-empirical ab initio method is ... High level quantum chemical calculations are then performed to further narrow down ...
NASA Website
... goals of this program have been to develop new, more effective methods for performing accurate ab initio electronic structure calculations and to ...
... Abstract : This report describes the development and application of ab initio quantum chemical methods that are especially relevant to the study of ...
Ab initio quantum chemistry methods are used to study the energetics of interactions of O atoms with
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...
Ab initio calculations of single and double differential cross sections for ionization by fast, charged particles within the framework of Born approximation are presented. In addition, a semiempirical method based on the asymptotic Bethe-Boron expansion i...
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...
...from such establishment, become void ab initio if the device comprising such shipment...2) of this section shall become void ab initio with respect to the person who...or other media, the equipment, and the testing method or quality controls to be used...
Code of Federal Regulations, 2011
NIST Computational Chemistry Comparison and Benchmark Database (Web, free access)�� The NIST Computational Chemistry Comparison and Benchmark Database is a collection of experimental and ab initio thermochemical properties for a selected set of molecules. The goals are to provide a benchmark set of molecules for the evaluation of ...
National Institute of Standards and Technology Data Gateway
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
E-print Network
the parameters for a polarizable force field from ab initio quantum-chemical calculations, and a rigorous method initio quantum- chemical calculations have become an increasingly impor- tant source of fitting dataParametrizing a polarizable force field from ab initio data. I. The fluctuating ...
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 the cluster (LiF)(4), ...
PubMed
... known GAMESS suite of computer codes [2]. Accurate ab initio methods pro- ... to the systematic improvement of standard quantum-chemical methods ...
quantum chemical method rather than an ab initio one. Although the approximate nature of semiempirical results must be stressed, such methods are reliable ...
... substantial impact; these tools are now incorporated in many ab initio codes ... Most commonly used quantum chemical methods possess one or the ...
... 11. TITLE (Include Security Classification) Analytic Methods Using Computer Algebra with Slater-Type Orbitals for Problems in AB Initio Quantum ...
... Title : Analytic Methods Using Computer Algebra with Slater-Type Orbitals for Problems in AB Initio Quantum Chemistry and Molecular Physics. ...
A simple method is described to adjust a potential energy surface to improve agreement with experiment. An application is made to the ab initio HCO potential energy surface.(AIP)
Energy Citations Database
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 ...
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 ...
The theory of trapping and diffusion of helium and hydrogen in metals is reviewed. The fundamental aspects of the behavior of these particles is emphasized and hence ab initio methods of calculation of interatomic potentials are described. In particular, ...
... 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 results of ab initio calculations based on the density-functional method and using the norm-conserving pseudopotentials for the ...
beyond the practical range of the standard ab-initio methods of quantum chemistry because of the large numbers of electrons involved. If one could ...
... Corporate Author : BATTELLE MEMORIAL INST RESEARCH TRIANGLE PARK NC. ... high level ab initio SCF and configuration interaction methods. ...
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 ...
... Abstract : Quantum chemical methods (ab initio, semiempirical, and Hartree-Fock) were used to calculate the energy of several phosphite ...
Aug 24, 2011 ... We have performed high-level ab initio calculations of the ground state and ... can be accurately treated by quantum chemical methods. ...
... crystal structures which are ordered superstructures of a parent disordered phase; a highly reliable statistical mechanical method (CVM) has now ...
... and many-body perturbation theory (MBPT) methods for the accurate inclusion of electron correlation in ab initio quantum chemical calculations of ...
... The interaction-induced dipole moment of the Ar-H2 van der Waals dimer was computed using ab initio quantum chemical methods in order to ...
(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
control of molecular dynamics; grid methods in the solution of time-dependent problems in quantum mechanics; ab initio calculation of potential energy surfaces and vibronic...
... Beta-(1-methyl-2-pyridinium) - alpha-cyano-4-styryldicyanomethanide was optimized using semi-empirical and ab initio quantum chemical methods ...
... Detailed analyses, including 6-31G' and MP2/6-31G* ab initio calculations, were performed for ... formed comparative quantum chemical calculations ...
... 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 ...
... the PRMD code - in Step 1- will be validated and further studied using ab initio methods to determine kinetic and thermodynamic properties of the ...
... solidification; Density; Nickel alloys; Liquids; Diffusion-liquid; ... erties of molten Ni-based alloys. The simulation method evolves ionic positions using ...
... More recently, extensive calculations on the nitrogen oxides were conducted employing the density functional method (ref 2) in conjunction with a ...
The CCSD(T) method, singles and doubles coupled-cluster theory plus a perturbational estimate of the
... Abstract : Electronic structure calculations using theoretical methods based on the linked-diagram theorem are reported for a series of dissociation ...
... Title : A Comparative Study of Nonlocal Density Functional Theory and ab initio Methods: The Potential Energy Surface of sym-Triazine Reactions. ...
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 ...
The methodology of nonempirical ab initio quantum mechanical calculations is reviewed as applied to the field of mineral surface chemistry and water-rock geochemical kinetics. The ab initio treatment of adsorption deals with the covalent forces between surface atoms and molecules either in solution or in the gas ...
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 ...
We perform ab initio molecular dynamics simulations to study the dissociation of NaCl in water. The potential of mean force (PMF) between the two ions is determined using the constrained-force method. The simulation windows corresponding to the contact and solvent-separated minima, and the transition state in between, are further ...
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 ...
Through the use of a molecular pseudopotential method, we determine the a approximate magnitudes of errors that result when electron affinity determinations of polar negative ions are made through ab initio calculations in which the use of a given basis set yields inappropriate values for permanent and induced dipole moments of the ...
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 ...
The reaction of C(3P) with H2S to HCS/HSC isomers is investigated with high level ab initio methods. Besides reaction energies to form HCS/HSC, the energetics and properties of different singlet/triplet H2CS reaction intermediates are studied. The combination of ab initio theory and crossed ...
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 ...
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 harmonic lattice dynamics have been evaluated ...
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 ...
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 ...
The interaction of CO{sub 2} and water is investigated by a combination of ab initio and SOLDRI-MM2 techniques. Ab initio results at levels of theory as high as MP2/6-311+G**//6-31G** are found to be in reasonable agreement with experiment. The R.{theta} potential energy surfaces generated for CO{sub 2}, H{sub 2}O ...
An approach is developed to enhance sampling for ab initio Monte Carlo and ab initio path integral Monte Carlo calculations of molecular clusters by utilizing an approximate potential as a guide to move in the configuration space more efficiently. The interpolated potential energy obtained by the moving ...
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 variation of several ...
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 ...
� � � 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 ...
A practical method of calculating the intrinsic reaction coordinate starting at a saddle point is proposed. The method has been used in combination with the analytical evaluation of the energy gradient for the calculation of the reaction coordinate on an ab initio potential energy surface. The reaction coordinates ...
Multiconfiguration relativistic Dirac-Fock calculations of KLL Auger energies are reported for neon, argon, uranium, and americium. These selected examples demonstrate the feasibility of this method to calculate completely ab initio, in intermediate coupling, Auger transition energies with a precision of a few eV. Comparison of our ...
takes the dyadic form: f = n n nf . Letting I denote the identity operator on the Hilbert space of the identity approximate integral method on modern ab initio algorithm development. Actually I focused on RI of the resolution of the identity approximate integral method on modern ab ...
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...
Reevaluating electron-phonon coupling strengths: Indium as a test case for ab initio and many Using indium as a test case, we investigate the accuracy of the electron-phonon coupling calculated, since for indium we find that can only be given to within approximately 10%. Indium is an ideal
The g-Hartree method is adapted to the direct ab initio calculation of transition energies in atoms. For the elements He(Z=2), Li(Z=3), Be(Z=4), Ne(Z=10), Mg/Z=12) and Ar(Z=18) all ionization energies have been computed and found to agree with available e...
A simple method to estimate the atomic degree Hessian matrixof a nanosystem is presented. The estimated Hessian matrix, based on themotif decomposition of the nanosystem, can be used to accelerate abinitio atomic relaxations with speedups of 2 to 4 depending on the sizeof the system. In addition, the programing implementation for using thismethod in a standard ...
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 converges rapidly to ...
We present an ab initio quantum theory of the finite-temperature magnetism of iron and nickel. A recently developed technique which combines dynamical mean-field theory with realistic electronic structure methods successfully describes the many-body features of the one electron spectra and the observed magnetic moments below and above ...
. 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 ...
The recombination dynamics for the SiH2 +SiH2 = SiH2 reaction are studied by quasiclassical trajectory methods using a global potential-energy surface fitted to the available experimental data and the results of various ab initio calculations. The potenti...
An approach is presented for the evaluation of the two distinct types of one-electron integrals arising from the ab initio pseudopotentials introduced by Kahn and Goddard. The integrals are shown to reduce to a sum over products of angular and radial integrals, the latter being approximated by power and asymptotic series combined with appropriate recursion ...
Atomistic and ab initio methods are used to study structural and electronic properties of perfect and defective chalcopyrites, specifically, ZnGeP2 and CdGeAs2. These materials are important due to their suitability for nonlinear optical applications in t...
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.
A careful comparison of some properties of systems of helium atoms in the liquid and solid phases is performed for several ab initio two-body potentials from the literature. Additional contributions from a three-body potential are considered as well. The multiweight diffusion Monte Carlo method is employed to quantitatively compute the ...
The potential barriers for the internal rotation of silole dimers are studied theoretically using the ab initio molecular orbital method at the RHF/6-31G** level of calculations. In 2,2{prime}-bisilole, it is found that the anti-conformation is the most stable structure in the ground state and that the potential barrier height for ...
The effects of electron-hole interaction on the optical properties of a variety of materials have been calculated using an ab initio method based on solving the Bethe-Salpeter equation. Results on selected semiconductors, insulators, and semiconducting polymers are presented. In the cases of alpha-quartz (SiO2) and ...
The authors have calculated the band structures of organic conductors TTF-TCNQ and {beta}-(BEDT-TTF){sub 2}I{sub 3} using the ab initio plane-wave pseudopotential method within the local-density approximation (LDA). The Fermi-surface shape and the origin of bands near the Fermi level are investigated for each compound.
Ab initio methods are used to study the formation of hydrogen-bonded complexes of cis-1,2-diazene with trans-1,2-diazene, cis-1,2-diazene, and ethylene. These reactions have negligible activation enthalpies when the effects of electron correlation are included. Calculated and experimental free energies of activation are mostly entropic ...
The ab initio calculation of electronic energies for numerous configurations of HCO and HOC, and a novel method for fitting the energies to a global surface are reported. This surface is used to calculate all the bound vibrational states of nonrotating HCO and DCO using the Watson Hamiltonian. Some quasibound vibrational states are ...
We present a formulation of ab initio electronic structure calculations in a finite magnetic field, which retains the simplicity and efficiency of techniques widely used in first principles molecular dynamics simulations, based on plane-wave basis sets and Fourier transforms. In addition we discuss results obtained with this method for ...
We have studied structural and dynamical properties of Mg2Sn by employing an ab-initio pseudopotential method and a linear response scheme, within the generalised gradient approximation. The calculated lattice constant, bulk modulus and pressure derivative of bulk modulus are in agreement with previous ab-initio calculations and available experimental ...
The project began March 13, 2006, allocated for three years, and received a one year extension from March 13, 2009 to March 12, 2010. It has now completed 48 of 48 total months. The project was focused on using ab initio methods to gain insights into radi...
Electronic properties have an important role in the metabolism of benzo(a)pyrene (BP) and the mutagenic action of its metabolites. In this paper, the ground electronic state of BP is characterized by the ab initio molecular fragment floating spherical Gaussian orbital method, and a speculative structural-electronic mechanism is ...
The potential energy surfaces for the doublet pi and doublet sigma states in the collinear F+HH reaction have been calculated with ab initio restricted Hartree-Fock (GRHF) and GRHF-CI (configuration interaction) methods. The doublet pi state in the CI cal...
In this work, the structure of symmetric N2O3 was investigated using ab initio methods. Bond lengths and bond angles were determined using the 6-31 G* and the 6-311 G* basis sets using both SCF and MP2 theory. At the highest level of theory considered in ...
The barriers to internal rotation about the N-C bond of formamide and the formanide-H2O complex have been examined by ab initio quantum chemistry methods. Both selfconsistent field and correlated approaches have been utilized to determine the geometries, ...
There has been an interest in the study of hydrogen ion clusters. However, only positive clusters, Hn +, where n = 3m 5, 7, ..., have been discovered and successfully analyzed by meand of both experimental and ab initio theoretical methods (cf. Hirao and ...
Ab Initio electronic structure calculations using analytical energy derivative methods and automated potential energy surface walking techniques have been carried out on the tautomerization reaction path connecting formamide (F) H2N-CHO, through a transit...
The electron transfer (ET) properties of 10- and 12-vertex carboranes are investigated by the ab initio Hartree-Fock method within the Marcus-Hush (MH) two-state model and the Koopman theorem (KT) approach. The calculated value of the ET coupling matrix e...
The use of ab initio molecular orbital calculations to aid in the characterization, i.e., structures and energies, of metal halide complexes present in high temperature salt vapors has been investigated. Standard LCAO-SCF methods were used and calculation...
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...
We present a theoretical investigation of the electronic structure of an InAs monomolecular plane inserted in bulk GaAs. Our calculations are based on the ab initio self-consistent pseudopotential method. Both electrons and holes are found to be strongly ...
For the equilibrium immiscible Fe-Cu system, ab initio calculations using the projector augmented wave method identify the relatively stable structures of the metastable Fe25Cu75 and Fe50Cu50 alloys to be both of fcc and determine their corresponding lattice constants and cohesive energies. Some of the ab ...
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 ...
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 initio ...
PubMed Central
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 (2005)]. Recently, ...
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 ...
Starting from the 1980s and onwards, Valence Bond theory has been enjoying renaissance that is characterized by the development of a growing number of ab initio methods, and by many applications to chemical reactivity and to the central paradigms of chemistry. Owing the increase of computational power of modern computers and to ...
We present a method for the computation of cohesive and structural properties of solids. The method is based on a local orbital description of the wavefunctions, an ab initio pseudopotential construction for the ion-core potential, and a local density tre...
The recently introduced theory of self-consistent electron pairs is shown to be a viable computational method for the determination of ab initio correlated molecular wavefunctions. Features of this method over conventional approaches are presented includi...
A modification of the SCF-MO-LCGO method is proposed in the form of a qualitative ab initio method. Naphthalene is treated as a test case; good agreement between calculated and experiemental results is obtained. The capabilities of the method for quantum-chemical calculations are discussed.
Structural and spectroscopic properties of hydrazine, H(2)N-NH(2), it being a floppy or fluxional molecule in a vacuum, are investigated by means of ab initio molecular dynamics, ab initio path integral molecular dynamics, and ab initio ring polymer molecular dynamics ...
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 ...
Results from several commonly used approximate methods of evaluating electrostatic interactions have been compared to the rigorous, nonexpanded electrostatic energies at both uncorrelated and correlated levels of theory. We examined a number of energy profiles for both hydrogen bonded and stacked configurations of the nucleic acid base pairs. We found that the penetration ...
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 ...
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 ...
Progress is reported in development, implementation, and application of a spectral method for ab initio studies of the electronic structure of matter. In this approach, antisymmetry restrictions are enforced subsequent to construction of the many-electron...
This research concerned the development of new ab initio nonempirical quantum-theoretical methods and computational techniques for studying molecular properties related to those of advanced materials. Extensive computations were performed to demonstrate t...
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 ...
A initio quantum chemical methods are seeing increased application in a large variety of real-world problems including biomedical applications ranging from drug design to the understanding of environmental mutagens. The vast majority of these quantum chem...
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...
The objective of this work is to use in silico methods such as ab initio quantum and classical force-field methods to explore and develop an understanding for the enantioselective metabolism rates experimentally observed in the triazole fungicide bromuconazole. This directed stud...
EPA Science Inventory
We have developed an ab initio path integral molecular dynamics method based on the fragment molecular orbital method. This �FMO-PIMD� method can treat both nuclei and electrons quantum mechanically, and is useful to simulate large hydrogen-bonded systems with high accuracy. After a ...
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 ...
The nature of intermolecular interactions between aromatic amino acid residues has been investigated by a combination of molecular dynamics and ab initio methods. The potential energy surface of various interacting pairs, including tryptophan, phenilalanine, and tyrosine, was scanned for determining all the relevant local minima by a ...
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) can predict low-lying levels in p-shell nuclei. It is a challenging task to extend ab ...
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 fitted so that they ...
Cubic zirconia exhibits a soft phonon mode (X2-) which becomes dynamically unstable at low temperatures. Previous ab initio investigations into the temperature-induced stabilization of the soft mode treated it as an independent anharmonic oscillator. Calculations presented here, using the self-consistent ab initio ...
The ability of simple levels of ab initio molecular orbital theory to describe with reasonable accuracy the energetics of isotopic exchange processes is demonstrated. Three levels of ab initio molecular orbital theory have been surveyed. The first two levels are single-determinant Hartree-Foch ...
The lattice constants and cohesive energies of some possible metastable Cu-W compounds are obtained by ab initio calculation and the formation of a metastable phase at Cu75W25 is predicted for the equilibrium immiscible Cu-W system. The prediction is in agreement with the fact that a metastable hcp phase was indeed observed in the Cu75W25 multilayer films ...
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 ...
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 intensity was found to be ...
We build an 'all-electron' norm-conserving pseudopotential for boron which extends the use of ab initio molecular dynamics simulations up to 50 times the normal density {rho}{sub 0}. This allows us to perform ab initio simulations of dense plasmas from the regime where quantum mechanical effects ...
We develop a new ab initio many-body approach capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. This approach preserves translational symmetry and ...
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 all three bases and ...
The quadratic, cubic and semi-diagonal quartic force field of propene has been calculated at the MP2 level of theory employing a basis set of triple-? quality. A semi-experimental equilibrium structure has been derived from experimental ground state rotational constants and rovibrational interaction parameters calculated from the ab initio force field. ...
