bluuebunny/crossref_metadata_2025_split huggingface dataset:
An intermediate neglect of differential overlap model for second‐row transition metal species
Authors: Anderson Wayne P. , Cundari Thomas R. , Zerner Michael C. 
Published: January 2005

AbstractAn intermediate neglect of differential overlap (INDO) model for elements of the second transition series is described. Values of exponents for the radial portion of the Slater basis atomic orbitals, the orbital ionization energies, and the beta (or bonding) parameters for these elements are reported. Use of the model to investigate equilibrium geometries, relative energy ordering of geometric isomers, spectroscopic transition energies, energy ordering of state wave functions of different symmetry, trends in dipole moments, and equilibrium stretching frequencies is reported. The results indicate that the INDO method is capable of yielding quality results for species containing atoms of the second transition series.
Calculations using a set of evenly spaced S‐type gaussian functions
Authors: Jensen James O. , Leonard Joseph M. 
Published: January 2005

AbstractA basis set of evenly spaced S‐type Gaussian functions with common exponents is examined. Formulas for common one‐ and two‐electron integrals are derived. Because of thesymmetry of this basis set, a very compact two‐electron integral list is produced. The number of two‐electron integrals that must be stored is approximately eight times the number of basis functions. Use of this basis set in an SCF calculation is examined. Numerical results show that this approach works well for molecules containing only small atoms such as hydrogen, helium, or lithium, but that the method has problems with the core orbitals of heavier atoms. Procedures for augementing this basis set in calculations involving heavier atoms are examined.
A study on the electronic spectra of vinylpyridines and 1,2‐(dipyridyl)ethylenes. Molecular orbital calculations
Authors: Abu‐Eittah R. , Hamed Maher M. , Mohamed A. A. 
Published: January 2005

AbstractThe electronic absorption spectra of 2‐, 3‐, and 4‐vinylpyridines and 1,2‐(2,3‐dipyridyl), 1,2‐(2,4‐dipyridyl), 1,2‐(3,4‐dipyridyl), and 1,2‐(4,4‐dipyridyl) ethylenes have been investigated in polar and nonpolar solvents. A correlation has been made between the geometry of the molecule and the observed spectrum. Molecular orbital calculations have been carried out using the INDO/SCI procedure and a limited geometry optimization. The solvent effect at the MO level has been calculated. MO calculations predicted the existence of nπ* transitions that were not observed experimentally. The wave functions of the different CI states were calculated. The experimental transition energy as well as oscillator strength corresponded satisfactorily with the calculated ones. The observed transitions were assigned according to the results of MO calculations.
The discovery of the chemical evolution of singlet oxygen. Some current chemical, photochemical, and biological applications
Authors: Khan Ahsan Ullah 
Published: January 2005

AbstractFrom the speculations of G. N. Lewis in 1916, [J. Am. Chem. Soc.38, 762 (1916)], the spectral predictions of R.S. Mulliken [Nature122, 505 (1928)], and the quantum mechanical treatment by E. Hückel [Z. Phys.60, 423 (1930)], the three lowest states of molecular oxygen (3Σg−,1Δg, and1Σ) remained spectroscopic elusives until Gerhard and Lisa Herzberg [G. Herzberg, Nature133, 759 (1934); L. Herzberg and G. Herzberg, Astrophys. J.105, 353 (1947); G. Herzberg and L. Herzberg, Astrophys. J.108, 167 (1948)], precisely defined them by observed infared transitions. The excited singlets remained of interest mainly to atmospheric spectroscopists and astrophysicists, and research on these species was scarce. The discovery in 1963 by A.U. Khan and M. Kasha [J. Chem. Phys.39, 2105 (1963)] of the simple chemical production of singlet molecular oxygens by the aqueous reaction of hydrogen peroxide and hypochlorite released an explosion of research on the neglected species. Fifteen research symposia and research treatises confirm the broad range of chemical activities of singlet oxygen. The extension to biological systems is now proceeding, with surprising evidence of involvement of natural processes, including the action of singlet oxygen in white blood cell phagocytosis.
Dipole moments, transition moments, oscillator strengths, radiative lifetimes, and overtone intensities for CH and CH+ as computed by quasi‐degenerate many‐body perturbation theory
Authors: Kanzler Alfred W. , Sun Hosung , Freed Karl F. 
Published: January 2005

AbstractThe correlated, size‐consistent, ab initio effective valence‐shell dipole operator (μv) method is used to calculate dipole moments and transition dipole moments of the CH molecule and transition dipole moments of the CH+ ion as a function of internuclear distance. The dipole and transition dipole moments computed here compare well with those of other accurate ab initio methods. The transition dipole moments are then used to calculate oscillator strengths and radiative lifetimes for the A → X and B → A transitions of the CH+ ion and the A → X transition of the CH molecule. Comparisons are made with the best available theoretical and experimental lifetimes. Finally, the CH ground‐state dipole moment function is used to evaluate overtone intensities and to examine simple models of the CH overtone intensities in polyatomic molecules.
A generalization of the method of stimulated emission pumping
Authors: Tersigni Samuel H. , Rice Stuart A. 
Published: January 2005

AbstractDrawing on the results of an analysis of the nature of the pulse that generates complete transfer of population from one to another level in a system with a discrete spectrum, a generalization of the method of stimulated emission pumping is proposed. It is shown that a small subset of the Fourier components of the optimal pulse will, if their relative amplitudes are the same as in the optimal pulse, generate almost as efficient a population transfer, thereby generating the opportunity to prepare a system in a selected state with a selected population.
Interaction between theory and experiment in molecular core electron spectroscopies
Authors: ÅGren Hans 
Published: January 2005

AbstractThe interaction between theory and experiment in the field of molecular core electron spectroscopies is reviewed. Those aspects that distinguish the theoretical descriptions of core and valence electron spectra are analyzed in particular. Differences in the theoretical approaches to atomic and molecular spectra in terms of scattering and many‐body theories are commented on. The molecular core electron spectroscopies are analyzed from a common point of view with respect to molecular orbital theory, many‐body theory, and the role of localization and local selection rules. A brief analysis is presented for the particularities that enter the calculations of core hole spectra. Solutions are described to computational problems posed by the quasi‐bound, highly excited nature of core hole states and by the large electronic relaxation following their creation. Two areas where the interaction between theory and experiment is particularly fruitful are briefly reviewed, namely, the theory of vibronic excitations in core electron spectra and the theory of the core photoelectron chemical shift.
Quantum rigid dipole in a permanent electric field. II. Model of librational motion in liquid water and ice Ih: Preliminary results
Authors: Kryachko Eugene S. , Yanovitskii Oleg E. 
Published: January 2005

AbstractA theoretical one‐body model of librational motion in liquid water and ice Ih is proposed within the quantum mechanical treatment of a rigid and pointlike dipole in a permanent electric field and the concept of the internal electric field justified for V‐structure of liquid water.
A BSSE‐free SCF algorithm for intermolecular interactions
Authors: Mayer I. , Vibók Á. 
Published: January 2005

AbstractA very simple modification of the usual (∼N4) SCF procedure is proposed, permitting the exclusion of basis set superposition errors (BSSE) in problems of intermolecular interactions. No a posteriori corrections are required. The results of this “CHA/F method” are numerically close to those of the Boys–Bernardi correction scheme but are free from the “overcompensation” characteristic of the latter at smaller distances.
Normal (decoupled) representation of electronegativity equalization equations in a molecule
Authors: Nalewajski Roman F. 
Published: January 2005

AbstractThe decoupled (normal) representation of the electronegativity (chemical potential) equalization equations, in which the hardness tensor {ηij}={∂μi/∂Nj} becomes diagonal, is examined in the atoms‐in‐a‐molecule (AIM) approximation; μi=∂E/∂Ni is the chemical potential of the i‐th AIM, Ni is its electron population, and E is the system energy. All relevant chemical potential, hardness, softness, and Fukui function quantities corresponding to the normal electron redistribution channels, Qy, are discussed and expressed in terms of the canonical AIM parameters. The normal chemical potentials, μγ=∂E/∂Qγ, provide a natural classification of the normal modes into three groups: (a) acceptor normal modes (μa < 0, positive mode Fukui function, hardness, and softness), (b) donor normal modes (μd > 0, negative mode Fukui function, hardness, and softness), and (c) polarization normal modes (μp=0, zero mode Fukui function, hardness, and softness). The implications of the normal mode analysis for the theory of chemical reactivity are briefly summarized.
Ab initio methods for large systems
Authors: Panas Itai , Almlöf Jan , Feyereisen Martin W. 
Published: January 2005

AbstractMethods for calculations on extended systems are proposed, in which long‐range Coulombic interactions are treated classically. The basic mode of description for the system is still in a quantum mechanical language, involving wave functions, Hamiltonians, etc. The electron density in a large molecular system is divided into suitable fragments, and the electrostatic potential generated by such a fragment at some distance away from it is then expressed by a generalized multipole expansion relative to a single point in space, conveniently taken as the center of charge distribution for that fragment. The computational effort required for evaluating the interactions involving those multipoles is modest and scales favorably (quadratically) with the size of the system. The remaining interactions, which need to be treated with conventional methods, i.e., with explicit one‐ and two‐electron integrals, scale only linearly with size in extended systems. An important characteristic of the approach is that, while the approximations and shortcuts introduced have a clear physical origin, they can be justified on strict numerical grounds, such that calculated energies and other properties are identical to those obtained with conventional methods.
Algebraic approximation to the Franck–Condon factors for the Morse oscillator
Authors: Palma A. , Rivas‐Silva J. F. , Durand J. S. , Sandoval L. 
Published: January 2005

AbstractAn algebraic approach is proposed to calculate the Franck–Condon factors for the Morse potential of diatomic molecules. The Morse oscillator is approximated by means of a fourth‐order anharmonic oscillator. In the second‐quantized formalism, this anharmonic Hamiltonian is diagonalized by way of the Bogoliubov–Tyablikov transformation. The Franck–Condon factors are estimated using the harmonic frequency equivalent and the recurrence relations for the Franck–Condon factors of the harmonic oscillator. Overlap integrals are shown for three band systems and compared with values calculated with an RKR potential. Excellent agreement is achieved.
On the quantum properties of adsorbed particles within the model of a hydrogen atom near a hard wall
Authors: Kovalenko A. F. , Sovyak E. N. , Holovko M. F. 
Published: January 2005

AbstractA hydrogen molecule near a hard wall was considered within the Heiteler–London method using the atomic orbits in the presence of the wall. Rapidly converging expansions of the atomic wave functions were proposed. The asymptotics were obtained and studied. The atomic dipole moment induced by the surface gave rise to a long‐range interatomic interaction. The covalent bond length increased near the wall. Depending on the orientation relative to the wall, the potential well can vanish. It is interpreted as an interaction between the atomic dipole moments. An approximation of the interatomic potential was proposed.
On Boolean algebra and its importance for the computer sciences
Authors: Löwdin Per‐Olov 
Published: January 2005

AbstractA brief survey is given of the abstract contentless Boolean algebra and its realizations to logic, class theory, and electric circuits as well as its applications to the software and hardware of the modern electronic computers. It is shown that three relations, 1 + 1 = 1, 1 + 1 = 0, and 1 + 1 = 10, correspond to three different realizations of the algebra, and that they, hence, represent an elementary example of a Gödelian branching point in the abstract Boolean algebra.
A project for an intelligent system: Vision and learning
Authors: Poggio Tomaso , Stringa Luigi 
Published: January 2005

AbstractOne of the most critical aspects of a truly intelligent system is the ability to learn, that is, to improve its own functionality by interacting with the environment and exploring it. In this paper, we argue that learning from exploring the environment should be the main goal in developing artificial intelligence. We also argue in favor of an integrated system—combining several state‐of‐the‐art aspects of artificial intelligence, such as speech, vision, natural language, expert systems—as the experimental platform with which to approach this problem. We then describe the main features of a project of this type, MAIA, which is under development at I.R.S.T. The vision components of the system will be discussed in some detail, especially the navigation architecture of the indoor robot available to MAIA. We will conclude outlining some initial learning problems that will be approached within the MAIA project, such as learning to recognize faces and learning to update the map of the Institute used for indoor navigation.
A theoretical study of electronic spectra of radical cations of some dihydroxynaphthalenes
Authors: Khan Zahid H. 
Published: January 2005

AbstractElectronic transition energies of radical cations of 1.2‐, 1.3‐, 1.6‐, and 1.7−dihydroxynaphthalenes are calculated using an open‐shell SCF method with configuration interaction. The results are critically analyzed and a correlation diagram is given that shows the energy‐shift and intensity variation in the electronic transitions when moving from one system to another, thus revealing the characteristic behavior of the transitions depending on the positions of the hydroxyl substituents. An interesting relation connecting the electronic spectroscopy with the UV photoelectron spectroscopy is suggested on the basis of which the first ionization potentials (IPS) of the substituted aromatic systems can be inferred from the calculated energy of the A‐type (HOMO → LUMO) transitions for their radical cations. Furthermore, the predictability of the IPs is found to be considerably increased with the incorporation of “molecular size” in the regression.
Thomas–Fermi–Dirac models of atoms constrained by nuclear cusp and long‐range conditions
Authors: Zhou Zhongxiang , Parr Robert G. 
Published: January 2005

AbstractThe traditional Thomas–Fermi–Dirac model of the electronic structure for a neutral atom is deficient in that it predicts an infinite electron density at the nucleus and a sharp cutoff of the electron density at a finite radius. This study was carried out to remedy these faults in the model. Extending an idea used earlier in Thomas–Fermi (TF) theory [Proc. Natl. Acad. Sci. U.S.A. 83, 3577 (1985)], the Thomas–Fermi–Dirac (TFD) energy functional is minimized under constraints ∫ρ(r) dr = N, ∫e−2kr▽2ρ(r)dr < ∞ and ∫(1 − e−k′r)ρ4/3(r)dr < ∞, with k and k′ determined by the nuclear cusp condition and the correct asymptotic behavior. Optimum coordinate scaling also is considered. It is found that the TFD model is substantially improved by constraining the minimization search domain of the energy functional in this way. Energies are given for five noble gas atoms, and Compton profiles for these atoms are calculated. The behavior of electrons in momentum space is improved in both this modified TFD model and in the corresponding modified TF model.
A search for properties which produce discrimination between cannabinoid psychoactivity and analgesic activity
Authors: Reggio Patricia H. 
Published: January 2005

AbstractOne long‐range goal of our work has been the design of cannabinoid analgesics with reduced psychopharmacological liability. We review here the progress we have made toward this goal. When we began our work on the cannabinoids, no cannabinoid analgesic had been reported that did not also possess significant psychoactivity. We approached the cannabinoid problem by calculating molecular reactivity characteristics (MRCS) of template molecules for each activity: (−)‐trans‐delta‐9‐tetrahydrocannabinol (Δ9‐THC) for psychoactivity, and (−)‐9‐nor‐9‐betahydroxyhexahydrocannabinol (9‐nor‐9β‐OHHHC) for analgesic activity. We then compared the MRCs of each template with the MRCS of a carefully chosen set of other cannabinoids (both active and inactive). Our focus in the calculation of MRCS was on accessible conformations of each subject molecule and on the molecular electrostatic potential generated in key planes by each accessible conformer. Our working hypothesis concerning the molecular basis of psychopharmacological activity in the cannabinoids was that activity is conferred by the set of molecular properties generated (1) by the orientation of the lone pairs of electrons of the phenyl group hydroxyl oxygen and (2) by the orientation of the carbocyclic ring and its C–9 substituent relative to this oxygen. Our working hypothesis concerning the molecular basis of cannabinoid analgesic activity was that activity is conferred by the set of molecular properties generated by the presence and relative location of two negative potential regions in the top half of the cannabinoid analgesic molecule. Our work thus far has revealed important steric and electronic features of the cannabinoids that may be used to enhance discrimination. We have shown that a simple structural feature, a C–9 substituent protruding into the α face of the molecule, can abolish or significantly diminish psychoactivity. We have also demonstrated that a free phenol group is not an absolute requirement for activity. Instead, we have found that compounds that do not possess free phenolic hydrogens, but that do maintain the orientation of the lone pairs of electrons of the “phenolic” oxygen toward the carbocyclic ring, exhibit selectivity toward analgesia.
The semiempirical approach to chemistry
Authors: Dewar Michael J. S. 
Published: January 2005

AbstractTwo kinds of quantum mechanical treatment are needed in chemistry: First, a treatment accurate enough to provide definitive solutions of chemical problems, in particular, the prediction of reactions and reaction mechanisms, without reference to experiment. As yet, treatments of this degree of accuracy are restricted to a few small atoms and molecules. Second, a treatment that chemists can use as a practical aid to their own research, on the same basis as mass spectrometry or NMR. Here, the need has been largely met by the series of progressively better semiempirical methods, in particular, those developed by our group. Since only the best and most expensive ab initio procedures are superior to ours and since the computing time they need is far greater, their use as a practical aid in chemistry is restricted. Our procedures, therefore, serve as a useful supplement to ab initio ones in areas where the latter cannot be applied effectively, as the leading ab initioists now fully recognize. Since the semiempirical approach is capable of almost unlimited further development, this situation is likely to continue in the foreseeable future. © 1992 John Wiley & Sons, Inc.
Group electronegativity and Fukui function studies of the substituent effects in aromatic and inorganic systems
Authors: Korchowiec J. , Nalewajski R. F. 
Published: January 2005

AbstractThe group electronegativities (GE) of molecular fragments, including the environmental contributions due to both the electrostatic interactions and electron distribution relaxation, and the Fukui function (FF) indices of the charge sensitivity analysis (CSA) are correlated with the known substituent effects in molecular systems. The semiempirical CSA in the atoms‐in‐molecules (AIM) resolution has been applied to substituted benzenes and square platinum complexes treated as illustrative examples. The calculated FF indices and GE are both shown to constitute adequate reactivity criteria that qualitatively reproduce the known substituent effects. The FF index (second‐order property) is found to be a more sensitive detector of the substituent influence than is the corresponding GE parameter (first‐order property). © 1992 John Wiley & Sons, Inc.
Eigenvalue distributions and asymptotic lines of the energy in alternant hydrocarbons
Authors: Hall G. G. , Arimoto S. 
Published: January 2005

AbstractThe bands of orbital energies for several polymeric species of alternant hydrocarbon are calculated. From these, the densities of states are graphed. By integration over the bands, the slope of the asymptotic line for the energy is calculated and compared with the energies of members of the same series calculated directly. For some series, the second, constant, term in the asymptotic line can also be calculated theoretically and compared with that derived from the molecular energies. The results for some related series indicate that for long molecules the number of Kekulé structures does not influence the major term in the energy. The extension of the argument to twodimensional arrays of hexagons is indicated and some results reported. © 1993 John Wiley & Sons, Inc.
Nonlocal approximation to the exchange and kinetic energy functionals: Application to metallic clusters
Authors: Glossman M. D. , Rubio A. , Balbáas L. C. , Alonso J. A. , Serra L I. 
Published: January 2005

AbstractThe nonlocal weighted density approximation (WDA) to the exchange and kinetic energy functionals of many‐electron systems proposed several years ago by Alonso and Girifalco in the context of density functional theory is used to compute, within the framework of the spherical jellium model, the ground‐state electronic density, chemical potential, and total energy of neutral and negatively and positively charged sodium clusters containing up to N = 800 atoms. From these calculations, we study the behavior of the total energies per atom, chemical potentials, ionization potentials, I(N), and electron affinities, A(N). These results are compared with analogous calculations using the well‐known Thomas–Fermi–Weizsäcker–Dirac (TFWD) approximation for the kinetic (TFW) and exchange (D) energy functionals. Calculations including the local density approximation (LDA) to the correlation energy in both WDA and TFWD functionals are also presented. © 1993 John Wiley & Sons, Inc.