bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neuartige Steroidale Orthoester durch intramolekulare Cyclisierung von Ethinylcarbinol‐Derivaten mittels Organylhypoioditen
Authors: Henkel T. , Beckert R. , Klemm D. 
Published: January 2005

Novel Steroidal Orthoesters by Intramolecular Cyclisation of Ethynylcarbinol Derivatives with Organic HypoioditesThe iodination of the 17β‐acetoxy‐17‐ethynylsteroid 2 using iodine/copper(II)‐acetate in combination with the nucleophiles acetic acid, water and methanol is reported. Examples for chemical modification of the products are described. A cyclisation occurs in the case of iodomethoxylation as a formal through‐space 1.4‐addition of the reagent forming a mixture of 4 isomer iodomethylen‐1,3‐dioxolanes. The configuration and ratio of the isomers as well as analytical data of this hitherto unknown dioxolane‐system are given.
Untersuchungen zu Mesityldimethylhalogensilanen als Schutzgruppenreagenzien für Alkohole
Authors: Weinzierl Uwe , Seidel Wolfgang 
Published: January 2005

Investigation on Mesityldimethylhalosilanes as Protectiv Reagents for AlcoholsThe use of mesityldimethylhalosilanes as protecting reagents for steroid alcohols was investigated. The resistance of the obtained silyl ethers was tested in various media. The reaction pathway of the acidic hydrolyses of the silyl ethers is explained.
Modelization by molecular mechanics (and X‐rays) of five‐membered heterocyclic nitramines
Authors: Delpeyroux D. , Blaive B. , Gallo R. , Graindorge H. , Lescop P. 
Published: December 2004

AbstractMolecular Mechanics (MM) calculations and X‐ray structures are compared for 1,4‐dinitro tetraazabicyclo(3,3.0)octanedione [1,4‐dinitro glycoluryl = 1,4‐DINGU]; 1,3‐dinitro‐4,6‐diacetyl tetraazabicyclo(3.3.0)octanedione [1,3‐dinitro‐4,6‐diacetyl glycoluryl = 1,3‐DINDAGU]; and 2,5,7,9‐tetranitro tetraazabicyclo(3.4.0)non‐anone (K 56). The agreement between geometries obtained by MM and X‐ray is good. The structure and the conformational states of the three model molecules are discussed. 1.4‐DINGU and K 56 are more symmetrical by MM than by X‐ray; this is due (at least in part) to packing in the crystal lattice. The parameters to be used in MM calculations, for treating stretching, bending and eclipsing forces in nitramines are given.
The Gibbs Energy Minimization Approach in the estimation of detonation, explosion and work production parameters of confined charges
Authors: Rigas F. , Pitsinis N. , Tsimogianni P. 
Published: December 2004

AbstractA method is suggested for the estimation of the physicochemical parameters associated with the entire phenomenon of detonation of explosive mixtures, exclusively containing the atomic species C,H,N,O, and expected to yield gaseous products. The equation of state applied for the products is a modified Abel equation. The calculation algorithm developed, constitutes the frame of construction of a computer program. The input required are the initial composition and apparent density of the explosive mixture and the final work production pressure. Sample applications for pure pentaerythrite tetranitrate detonation, TNT‐ammonium nitrate‐water slurries, and dry mixtures explosions are provided.
Synthesis, Properties and Performance of the High Explosive ANTA
Authors: Simpson R. L. , Pagoria P. F. , Mitchell A. R. , Coon C. L. 
Published: December 2004

Abstract3‐Amino‐5nitro‐1,2,4‐triazole(ANTA) was prepared and evaluated in terms of insensitivity and performance. The material is very insensitive to impact and moderately so to thermal stimuli. Performance was found to be inferior to 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB). The best synthesis of ANTA is a three‐step route using commercially available 3,5‐diamino‐1,2,4‐triazole.
A variational approach to the solution of poisson's equation in prolate spheroidal coordinates
Authors: Csavinszky P. 
Published: January 2005

AbstractThe present paper considers a charge distribution with an axis of rotational symmetry and formulates a variational principle in prolate spheroidal coordinates by which an approximate solution to Poisson's equation may be obtained. The feasibility of the suggested approach is demonstrated by a simple example for which the exact solution is known.
Ab initio mo calculations on the chlorophyll–water system and estimation of the structure of the special pair
Authors: Kashiwagi Hiroshi , Hirota Fumihiko , Nagashima Umpei , Takada Toshikazu 
Published: January 2005

AbstractAb initio LCAO SCF MO calculations were carried out on the chlorophyll–water system, which is considered as a moiety of the so‐called special pair in the reaction center of photosynthesis. The ionization potential and electron affinity of the system were 6.16 and 0.30 eV from the ΔSCF calculations. By using the atom–atom potential method for describing intermolecular interactions, we estimate the structure of the pair to be very close to that proposed by Shipman and others. The two major contributions to interaction energy are due to hydrogen bonds with water molecules and dispersion between the two chlorophyll planes, respectively.
On the red shift of OH stretching region vibrations in ice and water
Authors: Kryachko Eugene S. 
Published: January 2005

AbstractThe nature of the red shift of frequencies of the fundamental modes, v1 and v3, in the OH stretching region of the vibrational spectrum of ice (and, possibly, in water) under H‐bonding formation is explained in the framework of the continuum approach for the one‐dimensional infinite chain of water molecules represented as dipolar and polarizable OH oscillators vibrating in the definite force field. The explicit expressions in the form of the generalized cnoidal nonlinear waves describing these fundamental modes and obtained as the solutions of the nonlinear Klein–Gordon equation of motion, and their red shifts that are consistent with experimental observations, are presented.
Quantitative measures of similarity between pharmacologically active compounds
Authors: Bowen‐Jenkins Philippa E. , Richards W. Graham 
Published: January 2005

AbstractA theoretical measure of molecular similarity based on ab initio computations of electron density derived from molecular orbital wave functions is first applied to a model series (CH3CH2CH3, CH3OCH3, and CH3SCH3) and then to the rings in a series of prostaglandins and to some histamine H2 antagonists. Comparison in terms of valence electron density seems to be a good basis for structure‐activity studies.
Experimental and theoretical studies of small‐angle electron scattering by the water molecule
Authors: Takeuchi Munetaka , Nagashima Makoto , Tanaka Kiyoshi , Konaka Shigehiro , Kimura Masao 
Published: January 2005

AbstractThe total (elastic plus inelastic) intensities of 51 keV electrons scattered by water molecules have been measured over a range of 1 ≦ K = (4π/λ) sin(θ/2) ≦ 12 Å−1. A computer program, ELIC, has been written for calculating the total intensities of electrons scattered by free molecules. The intensities can be calculated with self‐consistent field and configuration interaction wavefunctions. The theoretical intensities based on a CI wavefunction are in good agreement with the observed intensities.
C. A. coulson and the surface energy of metals: The distribution of eigenvalues as a difficult problem in number theory
Authors: Čížek Jiří , Del Re Giuseppe 
Published: January 2005

AbstractAn article by Coulson on the relationhship of physics and mathematics has attracted our attention to problems already discussed by Titchmarsh, namely the distribution of quantum energy levels of a particle confined in a square or a cube with infinite potential‐energy walls. These problems are identical to some classical problems in the theory of lattice points, which belongs to number theory. They are seemingly simple, but in fact they are very difficult and not yet completely solved. We summarize the most relevant results from number theory. Whereas the beautiful theorems bearing directly on the error with respect to elementary estimates only provide indications concerning the order of that error; theorems concerning mean values can be used as a basis for a physicist's guess on its asymptotic mean value.This paper has also been intended to contribute to bridging the gap between quantum mechanics and number theory.
Modified molecular charge similarity indices for choosing molecular analogues
Authors: Richard Ann M. , Rabinowitz James R. 
Published: January 2005

AbstractToward the goal of defining a molecular charge similarity idex that best quantifies the concept of molecular similarity as it relates to biological activity, we have evaluated a variety of definitions of the molecular charge distribution function, ρ, for use in the charge similarity index formalism. Spatially distributed nuclear charges are incorporated into electron distribution functions to approximately account for the screening of core electronic charge and to model the net effect of the total charge distribution in a manner that better reflects the inherent relation to the molecular electrostatic potential. The resulting charge similarity indices are evaluated based on their sensitivity to relative molecule displacement and their ability to meaningfully group or order a simple set of molecular structures: CH3CH2CH3, CH3OCH3, and CH3SCH3.
Fluorine peroxide (FOOF): A continuing problem for normally reliable theoretical methods
Authors: Clabo D. Allen , Schaefer Henry F. 
Published: January 2005

AbstractThe greatest single success of modern computational quantum chemistry has been its ability to correctly predict the geometrical structures of molecules. The FOOF molecule stands in contrast to the overwhelming mass of comparisons between theory and experiment. This research shows that configuration interaction (CI) methods including all single and double excitations (SD) fail to predict the correct FOOF structure, even when high‐quality basis sets are employed.
Generation of a full active configuration space basis in terms of symmetry‐ and spin‐adapted antisymmetrized orbital products
Authors: Lam Miu‐To Brenda , Elbert Stephen T. , Ruedenberg Klaus 
Published: January 2005

AbstractA practical algorithm is described for generating a set of symmetry‐ and spin‐adapted antisymmetrized products of molecular orbitals (SAAPs) which form an orthogonal basis for a full active configuration space. The spin‐adaptation is completely general. The space‐symmetry adaptation is accomplished for the groups C∞v and D∞v.
Theoretical studies on conformational preferences of modified nucleic acid base N6‐(N‐glycylcarbonyl) adenine
Authors: Tewari Ravindra 
Published: January 2005

AbstractConformational preferences of modified nucleic acid base N6‐(N‐glycylcarbonyl) adenine, gc6Ade, have been investigated using the quantum chemical PCILO (Perturbative configuration interaction using localized orbitals) method. The multidimensional conformational space has been searched using selected grid points formed by combining various torsion angles that take favored values derived from energy variation with respect to each torsion angle individually. The theoretically predicted most stable, minimum energy conformation of the molecule is such that the substituent on N(6) spreads away from the imidazole moiety of the adenine ring, thus keeping distal orientation. The preferred molecular orientation is stabilized by an intramolecular hydrogen bond from N(11)H of the amino acid to N(1) of the adenine. The carboxylic group of the substituent is trurned away in relation to N(11)H…︁N(1) and is perpendicular to the plane through the rest of the moleculeThe alternative stable conformation corresponding to an 0.8 kcal/mol higher energy has a coplanar carboxylic group turned towards the same side as N(11)H…︁N(1) and is exhibited in the crystal structure of the nucleoside derivative, gc6A. Energetically, the carboxyl group may change its orientation over a wide range, without much destabilization. This suggests probing by the carboxyl group of the molecular environment in the vicinity of the anticodon in tRNA.
Resonances in nuclear, atomic, and molecular physics—an introduction with some examples
Authors: Elander Nils 
Published: January 2005

AbstractExamples from music and nuclear, as well as atomic and molecular, physics are given to introduce and illustrate the resonance concept. Some fundamental concepts of scattering theory such as the differential and the total cross section are presented. The concept of the collision complex is illustrated with a light particle scattering reaction in nuclear physics. The concept of channels is introduced, and this formalism (which is so far empirical in nature) is dressed in the language of quantum mechanics. Finally I show that our descriptions of phenomena in nuclear physics can also be used in atomic and molecular physics.
Intertwining methods in the theory of inverse scattering
Authors: Melin Anders 
Published: January 2005

AbstractIn this paper we make explicit constructions of a family Aθ of intertwining operators between the Schrödinger operator Hv = −Δ + v(x) and H0 = −Δ. The wave operators and the scattering matrix are expressed in terms of the Aθ, and some methods of inverse scattering are described.
Association of bound states of the coulomb potential with resonances of the coulomb potential perturbed by a barrier
Authors: Engelmann Alejandro R. , Natiello Mario A. , Höghede Mikael , Engdahl Erik , Brändas Erkki 
Published: January 2005

AbstractIn the present article we show how the bound states of the Coulomb potential may be associated with resonances that occur when this potential is perturbed by a barrier potential. The main idea is to trace the bound states on successive switching on of the barrier perturbation. It is found that those bound states that are localized inside the barrier are highly sensitive to variation with respect to the barrier height, whereas those that are localized outside are less sensitive. However, there are certain intervals for the barrier height when the role of being “a state localized inside the barrier” is shifted from one bound state to another. The result can be pictured as a “relay race,” where the “deliveries of the baton” are carried out over corresponding avoided crossings. The baton is ultimately handed over to a shape‐type resonance state.
Bond strength and bond angles for hybrid orbitals composed of arbitrary sets of orbital angular momentum quantum number
Authors: Zhan Chang‐Guo , (Liu Fan) Frank Liu , Hu Zhen‐Min 
Published: January 2005

AbstractAccording to the formulas obtained in the preceding paper, it may be used for all types of the hybridization with any set of azimuthal quantum numbers l, l = 0 through l = 5, and a complete theoretical data of bond angles and bond strengths are shown in this paper.
Spin‐free quantum chemistry. XXIII. The generator‐state approach
Authors: Matsen F. A. 
Published: January 2005

AbstractIn the unitary‐group formulation of quantum chemistry, the spin‐projected, configuration‐state spaces of quantum chemistry are realized by the irreducible representation spaces (IRS) of the freeon unitary group U(n), where n is the number of freeon orbitals. The Pauli‐allowed IRS are labeled by the partitions [λ] = [2(N/2)−s, 12S], where N and S are the particle number and the spin, respectively. The generator‐state approach (GSA) to the unitary‐group formulation consists of (1) the construction of the overcomplete, nonorthonormal generator basis for each IRS; (2) the Lie‐algebraic computation of matrix elements over generator states; (3) the Moshinsky–Nagel construction of the complete, orthonormal Gel'fand basis in terms of the generator basis; and (4) the computation of matrix elements over Gel'fand states in terms of matrix elements over generator states.
Spin‐free quantum chemistry. XXIV. Freeon many‐body theory
Authors: Matsen F. A. 
Published: January 2005

AbstractWe present the freeon, singlet, unitary group formulation of many‐body theory as an alternative to the particle‐number‐conserving, spin‐projected, fermion, second‐quantized formulation. It is based on the generator‐state‐approach (GSA) developed in part 23 of this series. We develop C1, perturbation, coupled‐cluster, and random‐phase theories.
Point group symmetry adaptation in clifford algebra unitary group approach
Authors: Gao M. J. , Chen J. Q. , Paldus J. 
Published: January 2005

AbstractThe symmetry adaptation procedure of Chen et al. [Sciencia Sinica 23, 1116 (1980)], which can account for the invariance properties of the Hamiltonian with respect to any finite point group G, is both modified and adapted to the Clifford algebra unitary group approach (CAUGA). From orthogonal symmetry adapted Mo's, one first constructs a pure configuration many‐electron basis adapted to the chain U(ni) ⊃ G ⊃ G(s) in terms of the U(ni) Gel'fand–Tsetlin (GT) basis, where ni is the dimension of the irrep defining a given pure configuration, and G(s) designates the canonical chain supplying a unique labeling. The pure configuration basis is then coupled to the desired G‐adapted states using the point group Clebsch–Gordan coefficients and the U(n1) ⊂ U(n1 + n2) ⊂ …︁ ⊂ U(n) basis by using the permutation group outer‐product reduction coefficients. This basis can be expressed in terms of the U(n) GT basis by using the U(n) subduction coefficients (SAC'S). The SDC'S are particularly simple for the highest weight states (Hess's) of various subproblems, which can be in turn represented through the U(2n) two‐box Weyl tableaux of CAUGA. The non‐HWS's are obtained by applying the U(ni) lowering generators to the HWS's. In this way we can directly obtain the spin and point group adapted CAUGA basis. The procedure is illustrated on a nontrivial example.
More on basis set quality tests
Authors: Robertson Donald D. , Smith Vedene H. , Thakkar Ajit J. 
Published: January 2005

AbstractThe quality measure δ of Sordo and Pueyo is computed for 94 orbital basis sets for the atomic helium Hartree‐Fock problem and compared with various information theoretic quality measures reported previously by us for this data base. δ is in error often enough that it is unlikely to be a useful general purpose measure.
Some considerations on the sturmian approach to green's functions
Authors: Engelmann Alejandro R. , Natiello Mario A. 
Published: January 2005

AbstractThe Sturmian transformation is reviewed and some of its properties are discussed, in particular, its use in perturbative approaches, its connection with variational schemes, and its use for the study of resonances. One potential problem (Doolen) having no bound states is described exactly.
Rayleigh–Schrödinger perturbation expansions for a hydrogen atom in a polynomial perturbation
Authors: Vrscay Edward R. 
Published: January 2005

AbstractRayleigh–Schrouml;dinger (RS) perturbation expansions for the eigenvalues E(λ) of a hydrogen atom in the general polynomial perturbation V(r) = aλr + b>2r2, a, b > 0, are studied. When a2 = 2b, the ground state energy is exactly E(λ) = ‐(1/2) + (3/2)a>, i.e., the RS series is truncated. In the case a2 > 2b, the RS series is negative Stieltjes. In general, when λ < 0, a well of depth ω ≈ ‐a2/(4b2) (note the λ independence) is situated at rω = a/(2b|λ|). When a2 > 2b/N2, and interaction between this well and the hydrogenic state ψNLM(λ) is possible, thus creating a pair of asymptotically degenerate eigenstates separated by a “gap” δE(λ). The large order behavior of the RS coefficients E may be computed from the asymptotics of δE(λ), which is, in turn, related to the tunnelling integral. For excited states, stricter inequalities must be obeyed for Stieltjes behavior. The E(n)NLM may be calculated either numerically or in closed form via the “so(4, 2) Lie algebra technology” for such hydrogenic problems.
Some aspects of approach to equilibrium in classical and quantum systems
Authors: Kumičáak Juraj , Brändas Erkki 
Published: January 2005

AbstractInvestigations of general properties of time evolution of both classical and quantum systems show that the evolution (on a microscopic level) is reversible, and, if there is an approach to equilibrium, it exists only in the sense of weak convergence and necessarily in both directions of time. In this connection attempts to derive irreversibility and the approach to equilibrium in the sense of strong convergence and without any loss of information (using the so‐called Lyapunov converters) are discussed. After demonstrating their drawbacks, an alternative approach is proposed based on the spectral properties of the generator of the group. The relevant spectral criteria for the approach of both classical and quantum ensembles to equilibrium are given, and the decisive role of loss of information in obtaining stronger variants of convergence is emphasized. The asymmetry between initial and any other state —consisting of different levels of information needed to prepare the states—is proposed as an adequate explanation of irreversibility. The importance of the method of complex scaling in this context is discussed, and its application in proving some spectral properties in the quantal Hamiltonian formulation is stressed.
Spin‐Projected EHF equations
Authors: Pavlides P. , Sales K. D. 
Published: January 2005

AbstractExtended Hartree‐Fock (EHF) equations are developed for the general open‐shell case using a modified pair‐orthogonality‐constrained variation (POCV) method. The EHF energy is expressed in terms of corresponding orbitals that are required to remain orthogonal and paired for all arbitrary infinitesimal variations.The Euler equations for each set of orbitals are reduced to unique pseudosecular equations, the LCAO form of which may easily be derived. The Euler equations and the expressions obtained for the off‐diagonal elements of the ϵγδ (γ, δ = a or b) matrices for the closed‐shell case are identical to those obtained by Mayer, who used the generalized Brillouin theorem method. However, the present method yields equations for both closed‐ and open‐shell cases and for any spin state.
Analytical potential from ab initio calculations for the Fe+‐H2O and Feo‐H2O systems
Authors: González‐Lafont A. , Lluch J. M. , Oliva A. , Bertrán J. 
Published: January 2005

AbstractAnalytical intermolecular potentials for the Fe+−H2O and Feo−H2O systems have been determined from ab initio calculations. Interaction energies for a lot of points along the two potential energy surfaces were calculated using Huzinga's MINI−2 basis set. The results obtained were fitted to an analytical function containing 11 adjustable parameters that we have already used with success for the Fe2+−H2O system. The goodness of the generated intermolecular potentials is discussed.
Inclusion of relativistic effects into ZDO methods. II. Solavation of metal complexes
Authors: Boča Roman 
Published: January 2005

AbstractThe quasirelativistic CNDO/1 method has been in investigating the geometry, electronic structure, and redox stability of metal complexes. The systems of [Co(NH3)6]q and [MCl4]q, M being Ni, Pd, and Pt, have been studied. A modified Germer model of solvation has been implemented into the method. This yields reliable results on the redox stability of complexes in aqueous solutions. The calculated excitation energies resemble the electronic spectra of [MCl4]2− complexes.
New concepts in bonded functions theory II. Canonical set of high internal symmetry
Authors: Golebiewski A. , Broclawik E. , Witko M. 
Published: January 2005

AbstractA new definition of a canonical set of bonded functions has been introduced. For a given configuration with r singly occupied orbitals and given multiplicity, the set exhibits symmetry properties of a group of order r. It simplifies the evaluation of the energy matrix H as well as the orthogonalization procedure.