bluuebunny/crossref_metadata_2025_split huggingface dataset:
Highly accurate Gaussian basis sets for the atoms from H through Xe
Authors: Librelon P. R. , Jorge F. E. 
Published: September 2003

AbstractAn improved generator coordinate Hartree–Fock (IGCHF) method is used to generate highly accurate Gaussian basis sets (GBSs) for the atoms from H (Z = 1) through Xe (Z = 54). In this method the Griffin–Hill–Wheeler–Hartree–Fock equations are integrated using the integral discretization technique. From these basis sets the ground‐state HF total energies are calculated and compared with the corresponding values obtained with GBSs of the same size, generated with the original generator coordinate Hartree–Fock method, and with a numerical HF method. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 190–193, 2003
Investigation of the quality of standard sulfur basis sets for molecules using a new generator coordinate method approach: Application to 2,2′‐bithiophene
Authors: Duani Helena , Duarte Hélio A. , De Almeida Wagner B. 
Published: September 2003

AbstractIn this work we have applied the generator coordinate method (GCM) to analyze the quality of the standard 6‐311G** and 6‐311++G** Pople's basis sets for the sulfur atom at the Hartree–Fock level of theory. When using the GCM theory, it is necessary to uncontract the basis set to obtain information about the quality of the basis set. To study large molecules such as bithiophene, for which it is difficult to use uncontracted basis sets at the ab initio level, we have developed a technique that makes possible the use of contracted basis sets within the GCM theory. To test such an approach, we have studied small molecules containing the sulfur atom, such as H2S and SCl2. The results show the suitability of using contracted basis sets for these systems with the GCM theory. In the study of contracted basis sets for the bithiophene molecule, we proposed and tested a modified basis set containing additional diffuse functions on the sulfur atom in the light of the GCM approach. The current study enables for the first time the assessment of the quality of atomic basis sets inside a molecular environment. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 194–204, 2003
Investigation of the excited states of resveratrol and related molecules
Authors: Del Nero Jordan , De Melo Celso P. 
Published: September 2003

AbstractResveratrol, a natural product derived from grapes, is a phytoalexin with antioxidative activity. In this work we present initial results of an ongoing study of the geometry of the ground state and of the first two (singlet and triplet) excited states of resveratrol and the structurally related compounds diethyl‐stilbestrol‐stilbene and trans‐stilbene. The molecular geometries were optimized both at the semiempirical and ab initio (restricted Hartree–Fock/6‐31G*) levels, and the corresponding absorption spectra were calculated using the intermediate neglect of differential overlap/ spectroscopically parameterized with interaction of configurations (INDO/S‐CI) methodology. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 213–218, 2003
Insulator‐to‐metal transition on polyselenophene
Authors: Marçal Nei , Laks Bernardo 
Published: September 2003

AbstractIn this work we calculate the density of states (DOS) for long, finite one‐dimension polyselenophene (PSe) chains with an ordered and a disordered distribution of bipolaron defects. The theoretical model adopted is a combination of the simple Hückel model in which the compressibility of the σ framework is explicitly taken into account. The negative‐factor counting technique and the inverse iteration method were used to find the electronic DOS and the wavefunctions, respectively. Our results show the presence of extended (conducting) states at the Fermi level. This could be explained by the semiconductor–metal transition in highly doped PSe, according to the macroscopic electrical conductivity observed experimentally. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 230–236, 2003
Elastic and rotational excitation cross sections for electron–nitrous oxide collisions
Authors: Lee M.‐T. , Iga I. , Brescansin L. M. , Machado L. E. 
Published: September 2003

AbstractWe present a theoretical study on electron–N2O collision in the low energy range. More specifically, we report calculated elastic and rotationally inelastic differential, integral, and momentum transfer cross sections in the 1.5–30‐eV range. An optical potential is used to represent the electron–molecule interaction. The Schwinger variational method is used to solve the scattering equations. In addition, the adiabatic‐nuclei‐rotation approximation is applied to calculate rotational inelastic cross‐sections. The comparison between the calculated results and the available experimental and other theoretical data in the literature is encouraging. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 260–266, 2003
Influence of nonbonded interactions in the kinetics of formation of chalcogenol esters from chalcogenoacetylenes
Authors: Ramalho Teodorico C. , Martins Tales L. C. , Eduardo Luiz , Borges Pizarro , Figueroa‐Villar José Daniel 
Published: September 2003

AbstractThe influence of nonbonded interactions in the kinetics of formation of chalcogenol (thiol and selenol) esters from chalcogenoacetylenes was studied by molecular modeling. Using semiempirical and density functional theory methods it was possible to explain the differences between the reaction rates for the analogous sulfur and selenium chalcogenoacetylenes as well as evaluate the structural and electronic effects (nonbonded interactions) on the formation of the esters. The differences in the reaction rates can be explained in terms of the carbocation stabilization by the chalcogen atom. It is proposed that these differences are due to the differences in the intensity of the dominant interaction π/nY between the nonbonding orbitals of sulfur and selenium with the vacant orbital of carbon in the cationic transition state. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 267–273, 2003
Relativistic method to get analytic solutions for many‐body problems: Application to the H molecule
Authors: Nascimento D. L. , Fonseca A. L. A. 
Published: September 2003

AbstractWe present a method for solving many‐body problems that allows the usage of Klein‐Gordon–like equations and in which it is not necessary to take into account the spin of the particles, whose effect appears through orbital angular momentum. Hence, the method deals only with ordinary wavefunctions instead of the more complicated spinor wavefunctions of Dirac's theory. The general wave solutions are found to possess a very close resemblance to the corresponding classical solutions, which allow the usage of simple mechanic analogies to deal with the many‐body problem. The method is applied to the H molecule, yielding the correct value for the ground‐state energy and also an approximation for the associated vibrational energies. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 274–280, 2003
Relation between antioxidant activity and electronic structure of phenols
Authors: Lavarda F. C. 
Published: September 2003

AbstractWe describe a new physicochemical descriptor of the antioxidant activity of phenols, the energy difference between the two highest occupied molecular orbitals, which we believe will improve quantitative structure–activity relationship studies about these compounds. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 219–223, 2003
The use of neural networks for fitting potential energy surfaces: A comparative case study for the H molecule
Authors: Rocha Filho T. M. , Oliveira Z. T. , Malbouisson L. A. C. , Gargano R. , Soares Neto J. J. 
Published: September 2003

AbstractThe fitting of ab initio electronic energies of polyatomic molecules for different nuclear configurations is an active field in quantum chemistry and is an important step in the study of chemical reaction dynamics and for the determination of rovibrational spectra. The choice of a good‐fitting function and the decision as to which geometries are relevant for the problem remains a matter of feeling as a large number of ab initio points of good quality usually involves prohibitively large amounts of CPU times. More recently, the use of neural networks has drawn some attention for fitting potential energy surfaces (PES). Neural networks are generic function approximators for any required accuracy and are therefore well suited for fitting many‐dimensional PES. In this work we present a comparative study for the ground state PES of the H3+ molecule obtained fitting state‐of‐the‐art ab initio points. The PES is obtained using both a neural network and a polynomial function in Morse‐type symmetry‐adapted coordinates. The quality of the surfaces is asserted by computing the associated rovibrational spectra. The resulting energies are compared with known experimental results. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 281–288, 2003
A QM/MM hybrid simulation of 5‐hydroxytryptophan in solution
Authors: Amaral M. S. , Loos M. , Ito A. S. 
Published: September 2003

AbstractThe nonnatural amino acid 5‐hydroxytryptophan (5OHW) has been proposed as a fluorescence probe for protein structure, function, and dynamics studies. Relative to the natural fluorophore, tryptophan, 5OHW has a red‐shifted absorption edge, which permits selective photo excitation of 5OHW in the presence of W residues. In this work, we present results of quantum mechanics/molecular mechanics (QM/MM) hybrid simulation of a 5OHW zwitterionic molecule in a box of water, using the computational package THOR. The 5OHW zwitterion is described quantum chemically, applying the AM1 semiempirical Hamiltonian while the water molecules are treated classically by the extended simple‐point–charge model. The behavior of the dihedral angles χ1 and χ2 is discussed in terms of the exponential fluorescence decay in aqueous solution. Theoretical optical absorption spectra, obtained by INDO/S‐CIS semiempirical method either in vacuum or in the continuum model using an ellipsoidal cavity are discussed and compared with experimental data and recent results of INDO/S‐CIS semiempirical absorption spectra calculated from optimized geometries obtained with ab initio Hartree–Fock 4‐31G in gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 289–294, 2003
Pattern recognition and neural networks applied to structure–activity relationships of neolignans tested against Leishmania amazonensis using quantum chemical and topological descriptors
Authors: Costa Maria Cristina Andreazza , Barata Lauro Euclides Soares , Bergmann Bartira Rossi‐ , Takahata Yuji 
Published: September 2003

AbstractPattern recognition (PR) and neural networks (NN) were applied to structure–activity relationship studies of a series of neolignans tested against Leishmania amazonensis. Comparison of NN with PR methods revealed that the capability of the two methods are similar to classify the molecules in the different categories, but it was found that K‐nearest neighbors and NN are superior to SIMCA in the activity prevision of a new set of compounds. The applicability of these methods using quantum chemical descriptors and topological indices were investigated. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 295–302, 2003
Structural, electronic, and vibrational properties of BxNy(x+y= 6) clusters
Authors: Guerini Silvete , Piquini Paulo 
Published: September 2003

AbstractHere we studied the geometric, electronic, and vibrational properties of the BxNy(x + y= 6) clusters through ab initio density functional theory calculations. Additional coupled‐cluster theory restricted to single, double, and noniterative triple excitation single‐point calculations are performed for clusters close in energy (≤0.5 eV). Our results show that planar ring structures (except the B6) have deemed to have lower energies as compared with three‐dimensional clusters. A greater stability of the stoichiometric cluster B3N3is predicted, followed by the B4N2and B2N4clusters. The BN5cluster is deemed to dissociate in an N2+ BN3channel. The B3N3cluster is suggested as an initial step in the growth process of the hexagonal boron nitride (BN). Some available experimental results on these six‐atom BN clusters are considered and partly explained. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 329–335, 2003
A deterministic approach for global minimization of molecular potential energy functions
Authors: Lavor Carlile 
Published: September 2003

AbstractThe problem of minimizing a molecular potential energy function is an example of a global optimization problem. Computing the global minimum of this function is very difficult, because it typically has a very large number of local minima that grows exponentially with the problem size. Most of the methods developed to resolve this problem are stochastic or heuristic methods. In this article we use a deterministic algorithm based on a branch‐and‐bound method that employs techniques of interval arithmetic. Using this algorithm, we can guarantee that the actual global minimum is found. The proposed approach was successfully applied to a set of test problems containing up to 22 degrees of freedom. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 336–343, 2003
Semiempirical studies of the electronic structure of polyphenylene sulfide phenyleneamine
Authors: Giro R. , Galvão D. S. 
Published: September 2003

AbstractPolyphenylene sulfide (PPS) and polyaniline (PANI) are heteroatom‐containing polymers with unique properties. While PPS provides a good level of chemical and thermal stability, PANI is important due to its ability to form electrically conducting films. A combination of PPS and PANI, with alternating phenyleneamine and phenylene sulfide blocks, resulted in a new material combining the structural features of PPS and PANI. This copolymer is known as polyphenylene sulfide–phenyleneamine (PPSA). In this work we present geometric and spectroscopic studies on PPSA oligomers using the well‐known semiempirical methods PM3 (parametric method 3) and ZINDO‐S/CI (Zerner's intermediate neglect of differential overlap/spectroscopic‐configuration interaction). PM3 results show that long PPSA oligomers present alternating in‐ and out‐of‐plane rings with torsion angles about 60°. The ZINDO‐simulated spectra compare well with the available experimental data. The origin of the low PPSA conductivity is addressed in terms of electronic features presented by isolated polymeric chains. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 252–259, 2003
Ab initio potentials for weakly interacting systems: Homonuclear rare gas dimers
Authors: Laschuk Eduardo F. , Martins Márcio M. , Evangelisti Stefano 
Published: September 2003

AbstractA series of high‐level ab initio interatomic potentials for the homonuclear rare gas dimers He2, Ne2, and Ar2 is presented, with predictions of rovibrational spectroscopic parameters and second virial coefficients. These potentials were created by using d‐aug‐cc‐pVnZ, n = D,T,Q basis sets, MP4 and CCSD(T) correlation energy treatments, the counterpoise correction to the basis set superposition error, and extrapolation schemes for estimating complete basis set (CBS) limits. A careful FCI correction was added to our best He2 CCSD(T) potential. The characteristic parameters De, Re, k, and σ of the ab initio potentials were compared with those of reliable empirical and ab initio potentials. Our best results for He2 recovered 99.9% of Janzen's SAPT2 well depth Janzen, A.R.; Aziz, R.A. J Chem Phys 1997, 107, 914–919. In the case of Ar2, we recovered 99.8% of Aziz's HFDID1 well depth Aziz, R.A. J Chem Phys 1993, 99, 4518–4525. For neon, second virial coefficients typically came to within 0.5–1.0 cm3mol−1 of experimental values and rovibrational energy levels exhibited errors of about 1.4 cm−1. Our best argon results exhibited second virial coefficients in agreement of 0.25 cm3mol−1 with experiment and rovibrational energy level errors around 0.2 cm−1. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 303–312, 2003
Hyperconjugation effects of hydroxyl and amine groups on chemical shifts of neighboring carbon nuclei
Authors: De M. Carneiro José Walkimar , Dias Jacques F. , Tostes José Glauco R. , Seidl Peter R. , Taft Carlton A. 
Published: September 2003

AbstractSystematic investigations of conformational effects of the hydroxyl group on carbon or hydrogen chemical shifts of different types of alcohols reveal that, besides stereoelectronic effects, hyperconjugation with lone pairs may have a strong influence. In view of the growing use of chemical shifts in probing the structure of biologic molecules, we employed DFT/GIAO/NBO calculations at the B3LYP level for conformers obtained from partial optimization of structures resulting from 30° variations of the CCXH (XO, N) dihedral angles to verify if nitrogen responded in a fashion similar to oxygen. Although the hybridization and geometry of hydroxyl and amine groups are distinct, the lone pair on nitrogen reveals hyperconjugation with suitably positioned orbitals on alkyl groups. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 322–328, 2003
Shear viscosity calculated by perturbation theory and molecular dynamics for dense fluids
Authors: Da Costa Silva Fabrício , Coelho Luiz A. F. , Tavares Frederico W. , Cardoso Márcio J. E. M. 
Published: September 2003

AbstractIn this work, we propose a new model to calculate viscosity of dense fluids based on the reference part of the Weeks–Chandler–Andersen perturbation theory. The reference fluid intermolecular interactions are given by a repulsive soft‐sphere potential. The viscosity is calculated by means of a Chapman–Enskog equation corrected to high densities coupled with a density‐ and temperature‐dependent effective diameter. The viscosity is also calculated by molecular dynamics simulations in a wide range of temperatures and densities for fluids interacting by repulsive soft‐spheres potential. These results, obtained from molecular dynamics, are used to optimize the parameters of the effective diameter equation. To compute the contribution due to attractive intermolecular interactions, we use a temperature‐dependent term, obtained by the Stokes–Einstein relation and the results published by Straub (1992) for the self‐diffusion coefficient. The proposed model correlated experimental viscosity data from literature with absolute deviations less than 4%. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 79–87, 2003
An invariant‐preserving approach to robust finite‐element multibody simulation
Authors: Borri M. , Bottasso C.L. , Trainelli L. 
Published: September 2003

AbstractWe briefly describe the main concepts that have inspired a novel approach for the integration of general non‐linear structural and multibody dynamics problems within a finite‐element framework that includes geometrically exact beams. In this approach, a numerically robust family of second to fourth order accurate algorithms are devised, which retain several important qualitative features of the exact solution. Among these, we address frame indifference, invariance with respect to reference entities (such as beam axes and shell mid‐surfaces), and, for load‐free motions, preservation of the system total linear and fixed‐pole angular momenta and a rigorous bound on the system total mechanical energy. When constrained systems are analyzed, these results are obtained by additionally requiring at the discrete level the preservation of Newton's Third Law of Action and Reaction and the vanishing of the work of the reaction forces for each constrained body pair. As a result, the schemes exhibit full non‐linear unconditional stability according to the Energy Method. The underlying single‐step, two‐stage, implicit difference schemes provide tunable high‐frequency damping ranging from null (ρ∞ = 1) to asymptotic annihilation (ρ∞ = 0). Representative numerical exercises are included to illustrate the main features of the methodology.
A wavelet semidiscretisation of elastic multibody systems
Authors: Díaz J. , Führer C. 
Published: September 2003

AbstractIn this paper we consider a coupled system of elastic and rigid bodies. It can be mathematically formulated as a coupled system of ordinary and partial differential equations, often written in its weak form. The discretisation is performed by a Galerkin‐type ansatz in connection with a finite element approach or known eigenfunctions. Here, we demonstrate instead the use of a recently published Galerkin‐wavelet method and its application to obtain a reasonable small number of elastic modes.
Optimal control and real‐time optimization of mechanical multi‐body systems
Authors: Gerdts M. 
Published: September 2003

AbstractNumerical methods for the solution and real‐time optimization of parametric optimal control problems for mechanical multi‐body systems are considered. The equations of motion are given as a differential‐algebraic equation (DAE) system of index 3 augmented by additional index 1 constraints. It turns out that the sensitivity analysis of parametric nonlinear programming problems is of central importance for the numerical solution of the optimal control problem by a direct shooting method and its real‐time optimization. On the one hand, a sensitivity analysis of the discretized optimal control problem provides a real‐time approximation of the optimal solution of a perturbed optimal control problem. On the other hand, a sensitivity analysis of the projection method used for consistent initialization yields consistent initial values of sensitivity matrices needed within the iterative solution process of the direct shooting method. Two examples conclude the article.
Dynamic modeling in the simulation, optimization, and control of bipedal and quadrupedal robots
Authors: Hardt M. , von Stryk O. 
Published: September 2003

AbstractFundamental principles and recent methods for investigating the nonlinear dynamics of legged robot motions with respect to control, stability, and design are discussed. One of them is the still challenging problem of producing dynamically stable gaits. The generation of fast walking or running motions requires methods and algorithms adept at handling the nonlinear dynamical effects and stability issues which arise. Reduced, recursive multibody algorithms, a numerical optimal control method, and new stability and energy performance indices are presented which are well‐suited for this purpose. Difficulties and open problems are discussed along with numerical investigations into the proposed gait generation scheme. Our analysis considers both bipedal and quadrupedal gaits.
Blended Lobatto methods in multibody dynamics
Authors: Schaub M. , Simeon B. 
Published: September 2003

AbstractConvex combination of the L‐stable Lobatto IIIC method and the A‐stable Lobatto IIIA method leads to the new class of blended Lobatto methods. These integration schemes offer the possibility to adapt the numerical damping and asymptotic behaviour to the given tolerance and the stiffness of the multibody system. The paper introduces the method class and discusses advantages and disadvantages of numerical damping. Moreover, a parameter function is given, which optimizes the efficiency by studying the cost of accuracy. As examples, a linear equation and a stiff pendulum are simulated.