bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitroureas 1. Synthesis, scale‐up and characterization of K‐6
Authors: Mitchell A. R. , Pagoria P. F. , Coon C. L. , Jessop E. S. , Poco J. F. , Tarver C. M. , Breithaupt R. D. , Moody G. L. 
Published: December 2004

AbstractThe synthesis and characterization of 2‐oxo‐1,3,5‐trinitro‐1,3,5‐triazacyclohexane (K‐6), a cyclic dinitrourea, is described. The laboratory synthesis was scaled‐up to provide 1.6 kilograms of crystalline K‐6 which was used for performance testing. K‐6 was formulated with 5% Viton A and pressed to 96.5% theoretical maximum density (TMD). Performance measurements in the form of front surface velocity measurements (tantalum plate push) and 1‐inch cylinder expansion experiments indicate K‐6 will out‐perform HMX by 4% at early volume expansions. Thermal response and shock sensitivity experiments on K‐6 are also described.
Electrical Performance of Explosive‐Driven Switches for slapper detonator applications
Authors: Podlesak Michael 
Published: December 2004

AbstractTime dependent resistance measurements were performed on fast, high current electrical switches proposed for use in slapper detonators. The switches, consisting of a copper‐polymer‐copper laminate, are designed to conduct electrically after being impacted by an explosive‐driven copper flyer plate. The polymer film used in our experiments was Kapton (polypyromellitimide) and was expected to exhibit shock induced conduction at pressures of 9 GPa and above. While it is believed that shock pressures in the vicinity of 9 GPa were achieved in the switches, no significant shock conduction effect was observed. This was corroborated by observing identical electrical behaviour for switches based on Teflon (polytetrafluoroethylene) film, which is known to possess good insulating properties even under strong shocks. However, in spite of the lack of evidence of significant shock induced conduction in the Kapton based switch, its operation is satisfactory. The average switch closure resistance at practical voltage and current levels was found to be of the order of 0.15Ω, attained within a closure time of 10 ns to 20 ns. Also, the electrical characteristic of the switch performance was largely independent of the supply voltage, when a low impedance voltage source was used, though the closure resistance values displayed a large scatter with standard deviation of the order of 0.1Ω.
Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCFMOLC(LCGO) Methode. III. Das Cyclopropan (C3H6)
Authors: Preuss H. , Diercksen G. 
Published: December 2004

AbstractDas C3H6 wurde unter Berücksichtigung aller 24 Elektronen ab initio mit dem Allgemeinen Programmsystem/SCFMOLC(LCGO) Methode berechnet. Es ergab sich nach Variation des CC Abstandes ein Minimum der Gesamtenergie von −116.02 a.E. bei einem CC Abstand von 2.91 a.E. Die Ionisierungsenergie wurde zu 10.33 eV bestimmt.
Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCFMOLC(LCGO) Methode. IV. Das Äthylen (C2H4)
Authors: Diercksen G. , Preuss H. 
Published: December 2004

AbstractDas C2H4 wird im Gleichgewichtsabstand der Zentren unter Berücksichtigung aller 16 Elektronen ab initio unter Verwendung des Allgemeinen Programmsystem/SCFMOLC(LCGO) Methode berechnet. Es ergibt sich eine Gesamtenergie von −76.77 a.E. Die Ionisierungs‐energie beträgt dabei 10.55 eV.
SCFCI and SCF open‐shell studies of the base components of the nucleic acids
Authors: Kuprievich V. A. 
Published: December 2004

AbstractThe π‐electron structure of adenine, guanine, cytosine, thymine and uracil in their ground, ionized, singlet and triplet excited states are investigated by means of the SCFCI and SCF open‐shell methods. The calculations for singlets fit the maxima of the absorption bands well. The energy difference between the first and the second singlet states of adenine is found to be very small. The open‐shell method leads to the same relative ionization potential as does the SCF (with the integrals empirically corrected). The calculated energies of the triplet states almost coincide in the SCF open‐shell and the SCFCI approximation. The calculated transition energies to the first triplet state of the pyrimidines are higher than in the case of the purines. The value of the singlet–triplet separation energy of purines is in agreement with experimental data.
Simplified SCF calculations for σ‐bonded systems. II. The interhalogens
Authors: Pohl Herbert A. , Raff L. M. 
Published: December 2004

AbstractA series of simplified LCAOMOSCF calculations has been carried out on the ten possible interhalogen molecules. In the model only the bonding electrons are considered explicitly. The bonded electron pair is described by a single Slater determinant and all integrals are evaluated by unadjusted, semiempirical techniques. Equilibrium separations, binding energies, and potential curves are obtained for each molecule, and the effect of the Wolfsberg–Helmholtz parameter in the off‐diagonal term is studied in detail.Without empirical adjustment, calculated electronic energies are accurate to about 2% while the bonding energies are too low by about 1 eV. Equilibrium distances are too small. The observed trends of these properties, however, are in satisfactory agreement with experiment. If desired, a single empirical adjustment of the Wolfsberg–Helmholtz parameter, K, suffices to bring the calculated binding energies of the entire series into good agreement with experiment. Previously suggested empirical forms for K yield poor results here and alternate proposals concerning the best procedure for determining, a priori, the best values for this parameter are made.In general it is concluded that the approximations utilized in this work are compatible and well‐suited for the description of σ‐bonded systems.
Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCFMOLC(LCGO) Methode. IX. Das System (Li2H)−
Authors: Preuss H. , Diercksen G. 
Published: December 2004

AbstractDas System (Li2H)− wurde für eine Reihe von Kernlagen unter Berücksichtigung aller 8 Elektronen mit dem Allgemeinen Programmsystem/SCFMOLC(LCGO) Verfahren berechnet. Es ergab sich für die lineare symmetrische Anordnung ein stabiles Molekül mit dem Bindungsabstand RLiH = 3,41 a.E. und einer Gesamtenergie von −15,3874 a.E., die um 0,0114 a.E. (0,311 eV, 7,61 kcal/mol) tiefer liegt als die Summe der entsprechenden SCF‐Energien der Systeme LiH und Li−. Die Kraftkonstante der symmetrischen Schwingung ergibt sich zu k = 1,64722 × 106 dyn/cm, aus der die Frequenz zu ω = 1998,9 cm−1 berechnet wurde. Die Ergebnisse werden diskutiert.
Calcul de l'Énergie de Corrélation pour l'État Fondamental de la Molécule d'Acétylène
Authors: Čížek Jíří , Pellégatti Alain 
Published: December 2004

AbstractLes effects de corrélation dans la molécule d'acétylène sont étudiés à partir d'une méthode utilisant une technique de diagrammes analogues à ceux de Feynman. L'introduction de la réduction des intégrales électroniques atomiques diminue considérablement la valeur de l'énergie de corrélation.
Theoretical considerations of the electronic spectra of methyl flavins
Authors: Song Pill‐Soon 
Published: December 2004

AbstractMethyl groups in flavins are best treated by the group‐orbital approximation. The pseudo‐heteroatom approximation overestimates methyl hyperconjugation with the Pariser–Parr–Pople SCF–MO method. Singlet π → π* transition energies are calculated by various MO methods with differing degrees of sophistication, and the results from the PPP method agree reasonably with the experimental values. 2‐ and 4‐thioflavin analogs are also treated satisfactorily. The effects of position and number of the methyl groups on the spectra of flavins are described in detail. Rough estimates of the n → π* energies of flavins suggest that the lowest singlet excited state is (π, π*), consistent with the fluorescence and phosphorescence polarization data.
Wellenmechanische behandlung der protonisierung des äthylens unter berücksichtigung aller elektronen
Authors: Fratev F. , Janoschek R. , Preuss H. 
Published: December 2004

AbstractThe system C2H5+ has been investigated as ethyl cation and as protonated ethylene using the SCF–MO–LC(LCGO) method. Equilibrium distances and angles have been estimated by different potential curves. No difference in total energy was found between the π‐ and the σ‐complex.
Long‐range interactions in the ground and two excited states of the HeH+ molecule
Authors: Piela Lucjan 
Published: December 2004

AbstractThe long‐range interaction energies for different dissociation products of the HeH+ molecule have been calculated using the Rayleigh–Schrödinger perturbation theory up to the third order in the energy. The calculations were carried out for the ground state (He(ls2) + H+), the first excited state (H(ls) + He+(ls)) and the second excited state Π(H(2pπ) + He+(ls)). The unperturbed states correspond to the dissociation products denoted in parentheses. Assuming the overlap to be zero, expanding the interaction potential in the inverse powers of the internuclear distance R and using the familiarly known perturbation‐variational technique, the coefficients of various powers of R−1 in the energy expansion were evaluated. They correspond to different multipole‐multipole interactions. The potential energy curves of all three states under consideration were calculated for large values of R. Also calculated were the multipole polarizabilities of the hydrogen atom in the is and 2pπ states and of the helium atom in the ground state.
Bounds to second‐order perturbation energies (particularly dispersion) for excited states
Authors: Abdulnur Suheil F. 
Published: December 2004

AbstractUpper and lower bound expressions are derived to the second‐order energy relating to an unperturbed degenerate excited state in those cases where both the first‐order energy and the off diagonal matrix elements in the secular equation vanish, making use of the partitioning technique, operator inequalities and inner projection approach. These expressions, which involve an arbitrary basis, are then developed to yield reasonably good bounds to van der Waals dispersion energies for systems of the type H (first excited state) — other atom b (ground state). The particular choice of basis used in the development yields the latter bounds easy to evaluate by expressing them in terms of the ground state sum rule values, S(k) of atom b. This same choice is also utilized in Lindner and Löwdin's expressions [1] to obtain bounds to systems of the type H (ground state) — other atom b (ground state) that are comparable to those found by other more elaborate semi‐empirical methods.
Gaussian wave functions for CH3 and NH
Authors: Kari R. E. , Csizmadia I. G. 
Published: December 2004

AbstractGround state single determinant LCAO‐MO‐SCF wave functions, using a large contracted Gaussian basis set (6s, 2p, 1d/3s, 1p), have been computed for the 9 electron molecular systems of CH3 and NH. The minimum energies obtained using Roothaan's open shell SCF procedure for the planar equilibrium geometries were −39.5703 Hartree for CH3 and −55.8945 Hartree for NH. Additional properties such as electron populations and multiple moments were calculated from the planar wave functions.
Molecular one‐electron integrals over slater‐type atomic orbitals and irregular solid spherical harmonics
Authors: Steinborn E. Otto , Ruedenberg Klaus 
Published: December 2004

AbstractThe one‐electron integral over Slater‐type atomic orbitals centered at A and B and irregular solid spherical harmonics as operator centered at C is evaluated analytically by using elliptical coordinates and translation of the solid spherical harmonics from center C to either focus A or B. A special case is the three‐center nuclear attraction integral which is also evaluated by means of the Neumann expansion and expressed without associate Legendre functions of the second kind. The strict observation of the charge distribution concept leads to compact expressions for the integral. It has the further advantage that the charge density distributions which have been developed for the two‐center cases and used in calculations for diatomic molecules can be utilized.
The use of explicitly correlated, partially antisymmetric wave functions in atomic and molecular calculations
Authors: Simons Jack 
Published: December 2004

AbstractTrial wave functions, written as the sum of a configuration interaction expansion and an explicitly correlated term which is not antisymmetric, are proposed for use in calculating the electronic properties of atoms and molecules. A variational principle, modified to allow the use for such partially antisymmetric wave functions, is developed. It is shown that the consequences of partial antisymmetry on calculated expectation values can be estimated. The method avoids difficult three‐electron integrals which arise in other theories.
Electronic structure of long cumulene chains
Authors: Ukrainsky I. I. 
Published: December 2004

AbstractThe analysis of the equations of the unrestricted Hartree–Fock (UHF) method for polyenes CNHN+2 with even and odd N » 1 is carried out. The equations of the UHF method are shown to be the same in both cases. The comparison of the UHF method with the extended Hartree–Fock (EHF) method applied to large systems is performed. The ground state and π‐electron spectra of long cumulene chains CNH4 are treated by the EHF Method. The end effects are taken into consideration. It is shown that the EHF method gives a finite value of the first optical transition frequency and, at the same time, zero value of torsion barrier of end CH2–groups in long cumulene chains (N → ) in contrast to previous calculations of cumulenes by the Huckel method and the restricted Hartree–Fock method.
A comparative quantum chemical study of ethylcarbonium ion and hydroxymethylcarbonium ion
Authors: Tel Luis M. , Wolfe Saul , Csizmadia Imre G. 
Published: December 2004

AbstractNonempirical molecular orbital calculations of the energies of CH3CH (ethylcarbonium ion) and HOCH (hydroxymethylcarbonium ion) as a function of rotation about the CC or CO bonds and deviation from coplanarity at the carbonium ion center are reported. As expected, and in agreement with previous work, both carbonium centers are planar and there is no barrier to rotation in the planar ethylcarbonium ion. However, for the planar configuration at carbon, the conjugative interaction between oxygen and carbon produces a barrier to rotation about the CO bond of HOCH of 19.6 Kcal/mole.When a pyramidal geometry is imposed upon the carbonium ion center of CH3CH, a typical three‐fold barrier results. As the deviation from coplanarity increases there is a regular increase in the barrier height (1.72 Kcal/mole at the tetrahedral geometry), but the energy minimum remains at the same position in each case (60°). For HOCH, imposition of a pyramidal geometry on the carbonium ion center causes a change in both rotational barriers. One decreases slightly (from 19.6 to 15.4 Kcal/mole) and the other increases to 30.5 Kcal/mole. There is an accompanying change in the position of the minimum of the rotational potential, from 90° towards the gauche structure.
CNDO/2 and MINDO/2 energy band structures of some homopolynucleotides
Authors: Suhai S. , Ladik J. 
Published: December 2004

AbstractThe all‐valence electron band structures of the periodic DNA models polyC, polyT, and polyA have been calculated with the aid of the CNDO/2 and MINDO/2 crystal orbital (CO) method.According to the obtained results the valence and conduction bands are always of π type. The widths of the bands are usually larger in the CNDO case, than those obtained for the same systems in the PPP CO approximation. On the other hand the MINDO results show similar widths as the PPP ones. The forbidden bandwidths are by 3–4 eV larger in the CNDO/2 case, than in the PPP one, while the MINDO/2 CO method has resulted in similar gaps like the PPP calculation.
Spin projected extended Hartree‐Fock equations
Authors: Mayer I. , Ladik J. , Biczó G. 
Published: December 2004

AbstractThe (spin projected) extended Hartree‐Fock equations are derived and discussed in the general (“many λi”) case. The derivation is based on the corresponding generalized Brillouin theorem, substituting in its expression the spin projected DODS Slater determinant as a linear combination of determinants. The expressions obtained for the elements of the different matrices εcd (c = a or b, and d = a or b) occurring in the equations are analyzed. The transformation of the equations into the form of a pseudoeigenvalue problem and the LCAO form of the equations are given, too. Finally the relation to the Goddard's GF equations is discussed in detail.
Nondiagonal second order intermolecular forces for interactions involving molecules
Authors: Riera A. , Meath William J. 
Published: December 2004

AbstractVery often only “diagonal” second order energies, varying as an even power of R−1, occur in the multipole expansion of the interaction energy. However for many molecular interactions important “nondiagonal” second order energies, varying as an odd or even power of R−1 can arise. This point is emphasized by a general discussion and by a detailed specific example, the interaction of an ionized dipolar molecule with a nondegenerate atom. Also some useful theorems, on the orientation average of various types of second order energies, are derived.
Effect of the exchange integral K2s2p on the 2p‐orbitals of the 1P and 3P states of the beryllium isoelectronic sequence arising from the configuration (1s)2(2s)(2p)
Authors: Tatewaki Hiroshi 
Published: December 2004

AbstractThe 1P and 3P states arising from the configuration (1s)2(2s)(2p) of the Be isoelectronic sequence are investigated. In the single configuration approximation, the energies of the two states are expressed as E0 + K2s2p and E0 ‐ K2s2p, respectively. K2s2p is the exchange integral between the 2s and 2p electrons and E0 is the energy of a model in which K2s2p is deleted. First we calculate the 2s‐ and 2p‐orbitals in this model. Second, by taking account of K2s2p in this model, effects of this term on the 2p‐orbitals in the 1,3P states are investigated. In this manner, an explanation is given for the following facts which are obtained from a minimal Slater‐type orbital set; (1) for Be and B+, the 2p‐orbital of the 1P state is broader than that of the 3P state; (2) for C2+, the extension of the 2p‐orbital in the two states is almost the same; (3) for O4+ and Ne6+, in contrast to Be and B+, the 2p‐orbital of the 1P state is tighter than that of the 3P state.
Symmetry in the Heitler‐London method. I. The connection of the molecular point group with its electron permutation group in the Heitler‐London method
Authors: Ledovskaya E. M. , Petrashen M. I. 
Published: December 2004

AbstractThe connection between the electron coordinates permutation group and the molecular point group is exhibited in the framework of the Heitler‐London method. It is shown that the initial wave function of a molecule in the Heitler‐London method can be written in such a form, that the effect of the point group operations upon this function corresponds to the permutation of the sets of electron coordinates of the ions and the subsequent multiplication of this function by some constants.
Symmetry adaptation and the relation between the spin‐free and space‐spin formulations of electronic structure
Authors: Klein D. J. , Cantu A. A. 
Published: December 2004

AbstractAn information‐theoretic degree of symmetry adaptation of a ket with respect to a given group is introduced. Then the general equivalence between spin‐free electronic kets and antisymmetrized space‐spin kets is obtained so long as our attention is restricted to spin‐independent observables. It is noted that there are spin‐free kets for which there exists no single antisymmetrized space‐spin ket giving all the same expectation values; the converse is also noted.
The Coulomb hole in the 23S state of the helium isoelectronic sequence
Authors: Boyd R. J. , Katriel J. 
Published: December 2004

AbstractThe pair distribution functions evaluated for the 23S state of the helium isoelectronic sequence from the Hart and Herzberg correlated wave functions and those corresponding to the Hartree‐Fock approximation are used to determine the shape of the corresponding Coulomb holes. As a consequence of a discontinuity in the Hartree‐Fock solution between He and Li+, the Coulomb hole has a different shape for He than for Li+ and the other isoelectronic ions.
Generalized open shell SCF theory
Authors: Caballol Rosa , Gallifa Ramóan , Riera Josep M. , Carbóa Ramóan 
Published: December 2004

AbstractA generalized form of the coupling operator technique in SCF theory has been developed. In the formalism presented here, the monoconfigurational problem may be treated as a particular case of the multiconfigurational framework. The matrix form of the operators has been analyzed; in the LCAO context a structure has been found which is very adequate for computational purposes.Some examples are also presented which show the usefulness of the theory, emphasising the CNDO and INDO approximations. Within the application of the method to ab initio calculations, some He and second row atoms states have been studied. The He first excited singlet is also studied, the result of the analysis of such a problem being that the nonorthogonality between the singlet functions of the fundamental and of the first excited states play a primordial role in the efficiency of the method.In no case have the calculation problems, appearing in the application of the theory, been of a more difficult nature than those normally found in the application of the formalism for closed shells.
An improved Hellmann‐type pseudopotential for atoms and molecules
Authors: Pohl Herbert A. , Fowler Donald R. 
Published: December 2004

AbstractThe concept of pseudopotentials offers much attractiveness for the quantum mechanical evaluation of the physical properties of atoms and molecules. The ideas of Hellmann, in which the repulsive and fermion character of inner electrons can be mimicked by an experimentally fitted, exponentially damped potential term, are especially attractive. Unfortunately, it is found that such a simple expression can only be used in a very limited number of cases, such as for the alkali metals, and even then fails for the simple case of lithium.The present study shows that the Hellmann idea can readily be extended by including a second “shielded potential” term evaluated from tabulated previous Hartree‐Fock calculations. The new expression for the model pseudopotential is both simple and effective. With it, the inner potential of any of the alkali metal atoms, including lithium, can be represented so that calculation of the molecular properties of the metal dimers can be accomplished. Calculations for Li2, Na2, and K2 show the binding energies and equilibrium interatomic distances to be quite well given, in agreement with both chemical experience and spectroscopic evidence.
Extended Hartree–Fock self‐consistent field with some results for berylliumlike atomic systems
Authors: Jucys A. P. , Lazauskas V. M. 
Published: December 2004

AbstractThe general methods of deriving the extended Hartree–Fock equations are described. The rules for going over from the energy expression in the ordinary method of calculation to that in an extended one are reformulated and illustrated. The extended Hartree—Fock equations for berylliumlike atomic systems based on the use of nonorthogonal radial orbitals are given and solved. The numerical values of overlap integrals and total energies are given and discussed.