bluuebunny/crossref_metadata_2025 huggingface dataset:
A Simple Method for Calculating Sympathetic Detonation of cylindrical, cased explosive charges
Authors: Victor Andrew C.
Published: December 2004

Sympathetic detonation involves the propagation of detonation between individual explosive‐containing devices. When many such devices are stored together, the possibility of mass propagation exists. With mass propagation, the entire stored mass detonates nearly simultaneously. Such propagation is the most feared hazard of such explosive items in transportation and storage environments because of its potential for sudden extreme damage and loss of life. Safety requirements, including those for insensitive munitions, are best met if explosive devices can be designed to minimize the risk of sympathetic detonation.

This paper presents a simple method for predicting the marginal conditions at which sympathetic detonation of cylindrical munitions just occurs (or just fails). The method can be easily and rapidly used in preliminary design studies to minimize subsequent hazard risks. It allows design and safety engineers to examine in minutes or hours what would take weeks or months of hydrocode calculations and months or years of field testing. The method involves algebraic solution of two‐dimensional shock propagation effects in an extension of Ferm and Ramsay's method for predicting shock initiation by spherical impactors(1). The donor case expansion velocity is calculated using the well‐known Gurney formula for cylinders as amplified by Dehn(2). The calculated initiation behavior of the acceptor charge(s) requires input data from wedge test results in the familiar Pop plot form, although a combination of card‐gap test data and failure diameter data can also be used (with reduced reliability) as a basis for estimating the Pop plot. The calculated results compare well with both hydrocode calculations and test data.
A facile pressing technique for the preparation of small calibre dual role explosive charge
Authors: Kumar A. S. , Samudre S. S. , Waghmare N. G. , Gharia J. S.
Published: December 2004

Small calibre shaped charges are prepared by the pressing method. The shaped charge performance is considerably influenced by the density gradient which is an inherent drawback associated with the pressing method. A new method, double action pressing technique has been developed which overcomes this problem and is amenable for large scale production. Properties of the charges prepared by the different methods especially with respect to the den sity gradient and performance against targets are presented and discussed.
Shock Consolidation of Aluminium Powder with SiC fiber reinforcement
Authors: Böttger W. , de la Haye J. , Prümmer Rolf
Published: December 2004

For the explosive compaction of Al 2024 alloy powder the influence of E/M ratio and detonation velocity of the explosive as well as the influences of powder microhardness and initial density are discussed. With a choice of parameters that gives a fully compacted aluminium sample the results of embedding single SiC fibers are described and a procedure to avoid fiber cracking due to shock loads is derived. First results for the compaction of samples with 38% fiber content are presented.
Combustion Mechanism of Glycidyl Azide Polymer
Authors: Hori Keiichi , Kimura Motoyasu
Published: December 2004

A combustion model of glycidyl azide polymer (GAP) is presented. Linear burning rate and temperature profile measurements of model samples led us to the conclusion that linear burning rate is controlled by N2 liberation process below the pressure exponent break point (2.3 MPa). Further, scanning electron microscope (SEM) photographs and Fourier transform infrared (FTIR) spectra of quenched samples by rapid depressurization of the combustor show that the N2 liberation process is strongly limited to the melt layer at the combustion surface and the profile of the heat release rate is probably δ‐function like. This fact enables the application of an asymptotic analysis to this phenomenon.
Initiation Criteria of High Explosives at different projectile or jet densities
Authors: Held Manfred
Published: December 2004

Test results of initiation threshold values with tungsten spheres of different diameters d and Lexan spheres of 76 mm diameter can be very well described by the u2d‐Held‐criterion where u is the cratering velocity or \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm v/(1 + }\sqrt {\varrho _{\rm t} /\varrho _{\rm p})} $\end{document}. For covered Composition B the initiation threshold value is 23 mm3/μs2. This value fits also shaped charge tests where the high explosive charge is also in a covered arrangement.
Optimization of the Flow Rate in High Pressure Liquid Chromatography of explosives
Authors: Kaiser Manfred
Published: December 2004

The height of a theoretical plate of 7 nitroaromatic substances and 2 aliphatic explosives was determined in dependence on the flow rate. The optimal flow rate for the maximum of the number of theoretical plates is in the area of 0.4 to 0.6 ml/min. For difficult separations this should be considered, since most HPLC instruments are used in the area of 0.7 to 1.0 ml/min. The amount of theoretical plates was calculated and presented in dependence of the flow rate. The height of a theoretical plate was plotted against the retention time and the capacity factor. The optimal area for the separation of the substances was at a capacity factor of 2 to 10. The van Deemter equation and the Knox equation were adjusted using 2,4‐dinitrotoluene. The data were fitted iteratively and the constants were determined. The equation for the conversion of the flow rate for other column diameters was shown, and using an example, the dependence of the flow rate on the column inner diameter and the flow rate was presented graphically.
Insensitive munitions (IM) and combustion characteristics of GAP/AN composite propellants
Authors: Oyumi Yoshio , Kimura Eishu , Hayakawa Shigeyuki , Nakashita Goro , Kato Kazushige
Published: December 2004

Sensitivities to the ballistic shock and burn rate characteristics of GAP/AN composite propellants were investigated. Nitrate esters, such as TMETN and NC, were very effective ballistic modifier that provided useable burn rate and pressure rate exponent for minimum signature propellant based on AN. Their low temperature mechanical properties became less sensitive to the temperatures with nitrate esters. Dioctyl adipate platicized propellant showed excellent mechanical properties at operational temperature ranges. The primary initiation mechanism of card gap test was not dominated by the mechanical properties. Although NC significantly increased the critical shock pressure, 14.8% HMX and AP were less effective to the sensitivities. GAP/AN propellants showed excellent IM characteristics to the ballistic shock applied here.
Ethical reflections on herbicide‐resistant crops
Authors: Madsen Kathrine Hauge , Sandøe Peter
Published: December 2004

The introduction of genetically modified (GM) crops has caused a fierce public debate in Europe. Much of the controversy centres on possible risks to the environment. A specific problem here is that risk perception of the scientific experts differs from that of the public. In this paper, risks associated with herbicide‐resistant crops are presented from the point of view of experts and lay people. In the public perception, herbicide‐resistant (HR) crops are troublesome because of their association with two technologies: genetic engineering of crops and the use of herbicides. These technologies are perceived as risky because they seem to share certain features: in particular, their long‐term effects are unknown and they are dreaded. Other value questions also come into play. The public seems to be concerned that risks are not outweighed by usefulness, that using HR crops is the wrong path to sustainable agriculture, that the individual's right to choose GM‐free products may be violated, and that these crops are unnatural. In contrast, on the issue of the uncertainty inherent in risk assessment, experts and the public seem to share a good deal of ground. Copyright © 2005 Society of Chemical Industry
A comment on the super‐secular‐equation in a symmetry adapted basis
Authors: Amos A. T.
Published: December 2004

The super‐secular‐equation has been introduced by Löwdin to discuss the Schrödinger equation in terms of a linearly dependent basis. The method is shown to be particularly simple when the basis is a symmetry adapted one. By expanding the secular equation a formula giving a good estimate of the eigenvalue is obtained.
Some remarks on the core resonance integral as used in the semi‐empirical π‐electron calculations
Authors: Sannigrahi A. B.
Published: December 2004

A simple semi‐theoretical expression for β, the core resonance integral as used in the semi‐empirical π‐èlectron calculations has been proposed. β's for some standard C  C and C  0 lengths have been evaluated with the proposed formula and the calculated values are compared with those obtained by other semi‐theoretical and empirical methods. Electronic spectra of ethylene, formaldehyde, trans‐butadiene and benzene have been calculated by a Pariser‐Parr‐like semi‐empirical method with the values of β thus obtained. The calculated spectra are found to be in good agreement with the observed ones.
A separated‐electron pair study of the electronic structure of the Li2O molecule
Authors: Lin Teng Ke , Ebbing Darrell D.
Published: December 2004

A separated pair calculation of the electronic structure of the Li2O molecule is described. Rather extensive calculations were made of the potential surface for symmetric configurations of Li2O using a double zeta Slater orbital basis. A linear configuration with LiO bond length of 1.71 Å is found to be most stable. The electron distribution and correlation effects are discussed.
The MC SCF theory: Method of one‐electron Hamiltonian
Authors: Kuprievich V. A. , Shramko O. V.
Published: December 2004

The one‐electron Hamiltonian method is developed to solve the variational equations of the MC SCF theory.

The many‐parameter family of the one‐electron Hamiltonian is derived and conditions for parameters to provide convergence of the SCF procedure to the energy minimum are obtained. A computation scheme based on the use of the one‐electron Hamiltonian is described.
A quadrupolar expansion for r
Authors: Salmon Lydia S. , Ruedenberg Klaus
Published: December 2004

An expansion is given for the inverse interelectronic distance in terms of the coordinates of the two electrons. The terms in the expansion contain the coordinates of the first electron with respect to two centers A, B and those of the second electron with respect to two centers C, D.
A simplified proof of a theorem about group representations
Authors: Reid Charles E.
Published: December 2004

It is a standard theorem of group representation theory that the dimension of an irreducible representation is a divisor of the order of the group. This paper gives a new, relatively simple proof, intended to make the theorem understandable to readers unfamiliar with algebraic integers.
Variational bounds for imaginary frequency polarizability and dispersion interaction constant
Authors: Braun P. A. , Rebane T. K.
Published: December 2004

A study is made of a variational principle which provides upper and lower bounds for the polarizability under a perturbation with imaginary frequency. As an example bounds for the imaginary frequency polarizability of atomic hydrogen and ensuing limits for the constant of van‐der‐Waals interaction of two hydrogen atoms are calculated.
An extended Hartree‐Fock method using corresponding orbitals: Application to lithium hydride
Authors: Burden F. R.
Published: December 2004

The corresponding orbital energy expression of Lefebvre and Prat [1] has been developed and used to obtain some extended Hartree‐Fock results for Lithium Hydride.
Theoretical studies of diamagnetic properties of the hydrogen molecule ion II. Effect of varying internuclear separation
Authors: Garrett Thomas B. , Zeroka Daniel
Published: December 2004

The diamagnetic susceptibility χ and magnetic shielding σ for H are investigated in the range of internuclear separations R = 1.6 a.u. to R = 2.4 a.u. according to a previously reported technique. From this data values of 〈χ〉 and 〈σ〉, for which nuclear motion due to zero‐point vibration and centrifugal stretching is taken into account, are calculated at 300°K. These averages are 〈χ〉 = −0.3902 α2a and 〈σ〉 = 1.096 × 10−5 c.g.s. units which are approximately 3.1% and 1.4% respectively, smaller than the equilibrium values.
Simple perturbation and perturbation‐variation treatments of the 1sσg and 2pσu states of H
Authors: Tung Eleanor W. , Sanders William A.
Published: December 2004

First‐order wave functions and binding energies of the 1sσg and 2pσu states of H are calculated by simple methods for internuclear separations between 0.2 and 10a0. An exact perturbation treatment of the lsσg state with a zeroth‐order function of the form N exp (‐sRλ/2) exp (sR μ2) yields only fair results. An alternative method starts with zeroth‐order functions of the form N exp (‐sRλ/2)[exp (‐sRμ/2) ± exp (sRμ/2)] for the 1 and 2 states, respectively. An approximate first‐order trial function is set up and the energies are determined variationally. For both states the results are comparable to those obtained by exact perturbation treatments of the same order.
Molecular orbitals of zinc phthalocyanine
Authors: Mathur S. C. , Singh Jai
Published: December 2004

Molecular orbitals of zinc phthalocyanine have been calculated with the help of a kind of extended Hückel technique. Coulomb and exchange integrals of the zinc atom have been approximated in a way equivalent to the valence state ionization energies of the particular metal orbital for a particular charge configuration. π‐electron charge densities over the atomic sites have been calculated and found in agreement with the observed results. π‐π* absorption (11000 cm−1 − 32000 cm−1) and charge transfer absorption (19000 cm−1 − 40000 cm−1) frequencies have also been calculated and found in agreement with the experiment.
An application of Green's functions to the study of the vibration‐translation coupling of trapped oscillators in a linear chain
Authors: Blaisten‐Barojas E. , Allavena M.
Published: December 2004

The Green functions and Kubo linear‐response theory are used to calculate the absorption coefficient of a collection of diatomic molecules embedded in a one‐dimensional lattice. The effect of the environment is restricted to the coupling between the molecular internal vibration and lattice vibrations. For the molecular oscillators, both harmonic and anharmonic models are considered. The absorption line shape is expressed in closed form whether the molecular frequency falls outside or within the allowed phonon frequency range. In both cases a frequency shift is found. In the anharmonic case there is a broadening of the absorption lines. Expressions for the shift and line width are given.
Sequence‐adapted molecular tensors: Algebraic methods and application to crystal field theory
Authors: Ellzey M. L.
Published: December 2004

Tensorial sets adapted to sequences of finite subgroups are applied to the crystal field problem, and a general method for generating sequence‐adapted molecular tensors using finite group algebra is formulated. All subgroup sequences of the abstract finite group G(24), isomorphic to the octahedral, O, tetrahedral, Td, and symmetric, S(4), groups are tabulated with explicit isomorphisms provided. The sequences fall into eight equivalence classes. A catalog of irreducible representations of G(24) adapted to a member of each of the eight sequence classes is given together with the transformations which generate representations adapted to all other sequences. With this data it is possible to systematically generate tensorial sets adapted to any sequence of a realization of G(24). Unitary transformations which adapt conventional forms of first‐ and second‐rank irreducible tensorial sets of the rotation group to the eight sequences of the octahedral group are provided. Forms suitable for use with magnetic fields are included. The problem of a d1 ion in a trigonal crystal field is treated with sequence‐adapted molecular tensors, and the utility of different sequences for descent in symmetry is discussed.
Integrals of quantum chemical interest in bases of laguerre functions. I. Functions of order 2l+2
Authors: Moseley W. D.
Published: December 2004

Formulae are presented for the evaluation of some definite integrals in which the Laguerre orthogonal functions are contained. In some cases mechanical quadratures are to be preferred, and a scheme is presented for generating such a quadrature as it is needed.
Tunneling phenomena in three‐dimensional double‐well potentials
Authors: Carbonell R. G. , Kostin M. D.
Published: December 2004

The tunneling of a hydrogen atom through the barrier of a three‐dimensional double‐well potential is considered. From the time‐dependent Schrödinger equation, expressions are derived for the ensemble‐averaged probability density and for the probability that the hydrogen atom is in the reactant region, in the barrier region, or in the product region. It is found that when thermal vibrations are not taken into account, the ensemble‐averaged probability density may oscillate with time about its equilibrium value. When thermal vibrations are included, the oscillations become damped and the probability density approaches equilibrium. The tunneling rate is found to decrease considerably for increasing barrier thickness and barrier height.
Icosahedral irreducible tensors and their applications
Authors: Boyle L. L. , Ożgo Z.
Published: December 2004

After a discussion of different concepts of anisotropy with reference to the icosahedron, the unusual problems surrounding the construction of icosahedral irreducible tensors are discussed. Tables of these tensors are then presented and applied to orbital problems, molecular polarization phenomena and to the construction of projection operators.
Half‐Projected and Projected Hartree‐Fock Calculations for Singlet Ground States. i. four‐Electron Atomic Systems
Authors: Smeyers Yves G. , Doreste‐Suarez L.
Published: December 2004

The half‐projected Hartree‐Fock function (HPHF) for singlet states is defined as a linear combination of two Slater determinants, which contains only spin eigenfunctions with even quantum number. Using a self‐consistent procedure based on the generalized Brillouin's theorem, the RHF, HPHF and PHF functions are deduced for the ground states of the Li−, Be, B+, and C2+ systems, in a limited basis set. It is found that the HPHF function yields better energy values than the RHF function, very close to that of the PHF one. The HPHF scheme seems thus to be useful as a substitute for the PHF model, specially in the case of large electronic systems in which the latter method becomes unmanageable.
Group theoretical methods for determining permitted terms of the electronic states of complexes in crystals. III. The use of plethysm for classification of the permitted terms of impurity complexes in crystal
Authors: Men B. A. , Cherepanov V. L. , Men A. N.
Published: December 2004

A procedure for the use of the plethysm operation for classification of the permitted electronic terms of impurity complexes in a crystal is presented. The cases of polyatomic symmetrical complexes are discussed as examples.
Molecular orbital studies on small molecules using H2+‐type elliptical basis orbitals. Application to H2+, H2, He2++ and H3+
Authors: Llaguno Claro T. , Gupta Shiv K. , Rothstein Stuart M.
Published: December 2004

H2+‐type elliptical orbitals are defined in Section 1. These orbitals, which in elliptical coordinates involve a factor (1 + ξ)σ, are employed in variational calculations on the ground states of H2+ and H2 (Sections 2 and 3). Various choices of σ are explored for H2+, while two choices are used for H2 : the “boundary condition” (Equation 6) and the “cusp condition” (Equation 9) values. Variational energies are calculated and compared to the results of similar calculations. Section 3 concludes by employing the H2+‐type orbitals in LCETO‐MO‐SCF calculations on the ground states of H2 and He2++. For both molecules a four‐function basis set with two (nonlinear) variational parameters yields more than 99% of the Hartree‐Fock limit. Section 4 deals with LCETO‐MO‐SCF calculations on triangular H3+. Three four‐function basis sets are used, and the best energy is ‐1.2306 a.u., which is in reasonable agreement with the Hartree‐Fock limit, ‐1.2999 a.u. Our best basis set is a four‐term two‐center expansion of the wave function with only one nonlinear variational parameter. Section 5 concludes the paper with a summary of the methods used to evaluate the integrals which arise in SCF calculations in the H2+‐type elliptical orbital basis.
Matrix elements for spin‐adapted configurations
Authors: Davidson Ernest R.
Published: December 2004

It is shown that the turn‐over rule which is used to simplify matrix elements between spin‐projected Slater determinants may also be used to simplify formation of matrix elements between any orthonormal set of spin‐coupled Slater determinants. The coefficients for the spin‐coupling may then be chosen freely to reduce the number of important configurations in the secular equation.
An investigation into the use of expansion methods in the calculation of chemical shifts and diamagnetic susceptibilities
Authors: Emanuel R. V.
Published: December 2004

The chemical shift and the diamagnetic susceptibility of the hydrogenic atom with magnetic dipole and origin of the external magnetic field vector potential noncoincident with the hydrogenic nucleus have been calculated from perturbation theory using a set of expansion functions whose radial parts are single exponent associated Laguerre functions. In contrast to hydrogenic expansion functions these functions give rapid convergence to the exact values of the second‐order energy summations when centred at the hydrogenic nucleus. The rate of convergence is fairly insensitive to the choice of expansion function exponent.
Electron correlation study for two‐electron atoms by a simple correlated wave function
Authors: Kagawa Takashi , Murai Tomokazu
Published: December 2004

The difference in the electron correlation between H‐ and other two‐electron atoms is clarified by the introduction of the r12 term in the wave function. By using the expansion of r12, a certain modification of the usual electron correlation factor 1 + Cr12 is introduced and its effectiveness is examined. Calculations are carried out for the ground state and the three lowest excited states (23S, 23P and 21P). The peculiar electron correlation in the ground state of H− is shown by looking at the Coulomb hole for closed‐ and open‐shelf models in comparison with those for other two‐electron atoms.
Dual‐basis orthonormality‐constrained variation method
Authors: Narita Susumu , I'haya Y. J.
Published: December 2004

The method of orthonormality‐constrained variation is extended using a dual‐basis set instead of a single orthonormal basis. The complete and the partial variation methods are discussed and applied to electronic systems. It is found that the present formulation leads to the most general equation in the coupling operator method.
Effective operators and the Z‐expansion method
Authors: Minchin P. E. H. , Wybourne B. G.
Published: December 2004

The application of effective operators in the Z‐expansion method is explored using hydrogenic functions. The relevant perturbation summations are evaluated using unit tensor operators and the results applied to the 1s22s22p2 + 1s22p4 complex of the carbon isoelectronic series.
Long‐ and intermediate‐range interaction between hydrogen atoms in the B1Σ state
Authors: Kołos W.
Published: December 2004

The energy of the hydrogen molecule in the B 1Σ state, for internuclear separations 12 ≦ R ≦ 20 a.u., has been computed using an 80‐term variational wave function depending explicitly on the interelectronic distance. The same type of wave function has been employed in the perturbation theory approach. Using the polarization approximation, and not expanding the interaction Hamiltonian, the first‐, second‐ and third‐order energies have been computed and higher‐order corrections have been estimated. The results show that in the region under consideration E and E represent the dominant contributions to the interaction energy in the B state.
On the use of Gaussian shell type basis orbitals for single‐center expansions. I. Evaluation of integrals
Authors: Poshusta R. D. , Agrawal V. P. , Moseley W. D.
Published: December 2004

Formulas are derived for all Hamiltonian integrals required for molecular computations using a novel basis for single‐center expansions. The basis orbitals depend exponentially upon α(r − ρ)2 where r and ρ are the distance from center to electron and to a variationally scaled spherical shell, respectively. Comparisons are made between these so‐called Gaussian shell orbitals (GSO) and the conventional GTO and STO bases for single‐center calculations. A preliminary comparison on H using a single GSO, a non‐integer STO, and a GTO gives the optimized energies: −0.51089 a.u., −0.50504 a.u., and −0.50422 a.u., respectively.
Many‐centered and one‐centered plethysms in the problem of many centers
Authors: Men B. A. , Varshavsky P. T. , Men A. N.
Published: December 2004

The concept of a “multi‐centered plethysm” for multinuclear problems is defined and studied. Schemes of links of atoms in molecules or complexes and corresponding schemes of the group reductions are considered.
Nonorthogonal radial orbitals for the configuration lnl
Authors: Jucys A. P. , Sabas K. V. , Kupliauskis Z. J.
Published: December 2004

The theory of treating the configuration n0ln1lNn2l by means of nonorthogonal radial orbitals is described. The expressions for the matrix elements of the nonrelativistic Hamiltonian are deduced. A table that enables one to obtain these expressions in terms of radial integrals for l = 0 and 1 are given. Numerical calculations are performed for the configuration 1s22s22p3p using generalized hydrogen‐like radial orbitals. The numerical values of the inter‐term energy differences are given and discussed.
Young operators and the Waller–Hartree spinfree method
Authors: Lim T. K.
Published: December 2004

The basic equivalent transformation Pσ = (−1)p (Pr)−1 as developed recently [6] is used to transform between the Young operators for a two‐row standard tableau and its conjugate two‐column standard tableau. These Young operators are shown to be the Löwdin spin projectors in the spin function‐dependent methods and the spin projectors in the spin function‐free methods. The sandwich operator of Gallup and the last diagonal element of the matric basis of Matsen are shown to be the special cases of our more general matric projectors. Several different forms of the Löwdin spin projectors, spin projectors, and matric projectors are shown and their relations are discussed.
Improved convergence of self‐consistence procedures in the MC SCF theory
Authors: Kuprievich V. A. , Shramko O. V.
Published: December 2004

To obtain optimized orbitals within the MC SCF theory, the energy surface near a chosen point is approximated by a quadratic function of independent matrix elements of a small orthogonal orbital transformation. The method of a second‐order one‐electron Hamiltonian (OEH) is developed on the basis of this approximation. A procedure is proposed to define step coordinates, insuring a rapid descent along an average‐energy surface also in the cases when the matrix of second energy derivatives has eigenvalues negative or close to zero. The results obtained in applying the OEH method for the calculation of ground and triplet states of uracile in the π‐electron approximation are discussed. When a complete matrix of the second energy derivatives is used, the self‐consistence procedure is quadratically convergent. An exponential, yet rapid enough convergence is provided by a simplified computation scheme neglecting cross derivatives.
Extended Hückel theory of hydrogen‐molecule interactions
Authors: Barriel J. M. , Riera J. M. , Sanz F. , Caballol R. , Vidal M. , Carbó R.
Published: December 2004

A computational technique within the Extended Hückel frame‐work for the calculation of the hydrogen‐molecule interaction energy is described. The procedure is ten times faster than the usual diagonalization procedure.

The algorithm consists of transforming the generalized secular equation to give a bordered‐diagonal matrix secular equation, which is solved by means of an efficient bisection technique.

As an example, two problems are discussed: (i) glycine intra‐molecular proton transfer process; (ii) interaction of the molecular fragments CH and OH.

An atomic SCF Gaussian basis set was used instead of the usual Slater type basis set.
Adiabatic perturbation theory for the degenerate case. II. Perturbation of degenerate bound states embedded in the continuum
Authors: Dmitriev Yuri
Published: December 2004

An adiabatic formula for the contracted Hamiltonian in a reference space containing bound‐state eigenfunctions of degenerate energy levels embedded in the continuum is derived. A general factorization theorem for the dynamic operatorSα(0, – ∞/λ) is proved, and the cancellation of the pole singularities in the perturbation series of the contracted Hamiltonian in adiabatic form is discussed.
A method for the construction of orthogonal spin eigenfunctions
Authors: Murty J. S. , Sarma C. R.
Published: December 2004

A method for the construction of the essentially idempotent and Hermitian diagonal elements of the matric algebra of the permutation group Sn is proposed. For the irreducible representation [λ] = [λ1, λ2] characterising a spin state S of an n‐electron system, it is found that this method generates the complete set of spin projections from the appropriate primitive spin functions. The method is applied to a 7‐electron system in the spin state S = MS = 1/2 and the results are listed in the Appendix.
Spin projections for even electron systems
Authors: Sarma C. R.
Published: December 2004

A new method is presented for obtaining the spin eigenfunctions of 2n electron systems in the spin state S and MS = 0. Using a modified Young operator the function for the state S, MS ( = S) of the system is first projected out. The projected function is then symmetrized over the last n particles and the weight lowering operator Š is then applied to it, resulting in a projection of the state S, 0. To within a multiplicative factor, the resulting function is identical with the one resulting from the vector coupling methods.
Angular correlation of electrons in the ground state of helium
Authors: Tatum J. Patrick
Published: December 2004

The spatial angular correlation of electrons in the ground state of the helium atom has been examined using configuration interaction and Hylleraas wave‐functions. It was found that, in general, the average angle between the electrons is not a maximum when the two electrons are at the same distance from the nucleus. For configuration interaction wave‐functions there is a position of the electrons for which the average value of the angle between the electrons is a maximum. Hylleraas wave‐functions do not show this behavior.
The N2 problem in molecular CI calculations
Authors: Meunier A. , Levy B. , Berthier G.
Published: December 2004

The possible existence of spurious terms increasing as the square of the number of electrons is theoretically proved for the CI treatments of molecules limited to single and double excitations, and is revealed by some numerical calculations (alcanes and juxtaposed hydrogen molecules). An improved perturbation scheme is suggested in order to evaluate the CI energy lowering more carefully. Covergence difficulties are found for larger systems (benzene).
Quantum mechanical tunneling in synaptic and ephaptic transmission
Authors: Walker Evan Harris
Published: December 2004

Quantum mechanical tunneling theory is applied to the problem of synaptic vesicle release and to the problem of electric transmission at the ephaptic junction. In the synapse the tunneling produces conformational changes in macromolecules to open and close vesicle macrogates. Quantum mechanical tunneling as a basis for charge transfer and physical release of vesicles at junction membranes provides a unified concept of ephaptic and synaptic transmission. Details of this model are in agreement with experimental data for miniature endplate potential frequency and delay effects as a function of polarization, osmotic pressure, and temperature. The theory accounts for anatomical specializations at the synaptic cleft and the narrow junction observed for the ephapse.
Calculation of molecular electric polarizabilities and dipole moments. II. The LiH molecule
Authors: Haley Lawrence V. , Hameka Hendrik F.
Published: December 2004

We use a variation–perturbation method to calculate the electric polarizabilities and the electric dipole moment of the LiH molecule. We obtain 4.455 for the perpendicular polarizability and 4.001 (×10−24 cm3) for the parallel polarizability. Our result for the electric dipole moment at equilibrium nuclear distance is 5.866, which is in excellent agreement with the experimental value 5.828 debye units.
The electronic structure and properties of pyrazine, its cation, and anion
Authors: Hinchliffe Alan
Published: December 2004

Gaussian orbital LCAO MO calculations are reported for pyrazine in its ground and first excited triplet state, together with calculations on its anion and cation. Energies, population analysis indices, and one‐electron properties are compared across the series in order to investigate the differences in electron distribution.
Perturbation theory within the variation method
Authors: Epstein Saul T.
Published: December 2004

Some of Moccia's formulas (Int. J. Quant. Chem. 8, 293 (1974)) for corrections to “not completely optimized variational parameters” are compared with those resulting from a perturbation theory analysis. It is not possible to choose the zero‐order Hamiltonian (at least not in any simple way) so as to get exact agreement, but one choice does come close.
Electron momentum distributions from valence‐bond wave functions
Authors: Gardre S. R. , Narasimhan P. T.
Published: December 2004

Momentum densities obtained from the Heitler‐London (HL) wave functions for diatomic molecules and those from the corresponding valence‐bond (VB) wave functions including ionic terms are compared. In each case they shown maxima in the direction perpendicular to the bond. However, the dependence of momentum densities on mutual orientations of the two electronic momenta is quite complex in the latter case. The improvement in the Compton profile on including the ionic terms is illustrated with the example of H2. The momentum denmsities obtained from the VB wave function constructed from orthogonalized atomic orbitals (OAO) have also been examined. The HL wave function with OAOS leads to the same momentum distribution as the repulsive state HL wave function constructed from overlapping AOS.
On invariance requirements in approximate SCF MO Theory
Authors: Nanda D. N. , Narasimhan P. T.
Published: December 2004

The invariance question int he CNDO and INDO levels of approximation is discussed with particular reference to one‐center and two‐center two‐electron integrals and rotation of molecule‐fixed coordinate axes. It is shown that asufficient condition for rotational invariance for the cone‐center two‐electron integrals is Jμμ = Jμμ, +2Kμμ, where J and K are the Coulomb and exchange integrals over orbitals μ μ′ with the same azimuthal quantum number. CNDO and INDO procedures, which explicitly employ Löwdin's orthogonalized basis set of atomic ortbitals (OAO) and differentiate between s‐, p‐, and d‐orbitals on an atom in calculating various integrals, have also been examined in relation to the rotational invariance requirement. An expression which satisfies rotational invariance for two‐electron Coulomb repulsion integrals over OAOS is also given.
Discrete and continuum contributions to multipole polarizabilities and shielding factors of hydrogen
Authors: Tanner A. C. , Thakkar Ajit J.
Published: December 2004

Discrete and continuum contributions to the multipole polarizabilities and shielding factors of atomic hydrogen are computed. The discrete series show logarithmic convergence which can be accelerated by the u‐transform. The continuum contributions increase with increasing multipole order and are already dominant in the quadrupole polarizability and shielding factor. The shielding factors have greater continuum contributions than the polarizabilities.
Projected BCS Tamm‐Dancoff method for molecular electronic structures
Authors: Takahashi Mitsuo , Fukutome Hideo
Published: December 2004

A new Tamm–Dancoff method for the ground and excited states of molecular electronic systems is developed. The method begins with a number‐projected BCS (PBCS) wave function and is generated by excitations of particle pairs from the degenerate geminals in the PBCS wave function. A direct optimization of the PBCS wave function is accomplished with successive Bogoliubov transformations so that one‐pair excitation terms in the Tamm‐Dancoff expansion of the ground state vanish (the generalized Brillouin theorem). The spin‐symmetry adapted first‐ and second‐order Tamm–Dancoff bases and matrix elements are calculated by means of the CI expansion of the PBCS wave function with natural orbitals that diagonalize the BCS geminal matrix. Numerical calculations are presented for the H4 system with D2h and D4h conformations and for methylene. The PBCS wave function is not a very good approximation for the ground state, accounting for only about half of the correlation energy. The second‐order Tamm–Dancoff correction improves the result as much as the double excitation CI. The Tamm–Dancoff terms consisting of two triplet pairs coupled to a singlet, and those relaxing the constraint imposed on the pairwise excitations in the PBCS wave function are important.
Shaping the density to fit one‐electron properties: Constrained RHF calculations on N2, FH, CO, and LiH
Authors: Zeiss G. D. , Whitehead M. A.
Published: December 2004

The molecular density required to give the correct values for one‐electron properties is rarely given by wave functions obtained from variation methods based on the total energy or the eigenvalues. Perhaps if we knew how the density should be shaped in any particular volume to fit a particular property, the whole molecular density might then be properly described to fit the whole volume. The secant‐parametrization procedure is used to constrain minimum basis set RHF wave functions for N2, FH, CO, and LiH to determine the effects of different constraints on RHF wave functions, and to see how constraints improve the quality of small basis set RHF wave functions. One‐electron property expectation values, energies, and unweighted and property weighted populations and electron density difference profiles are used to analyze the constrained wavefunctions. With the information from the constrained wave functions it should be possible to select a LCAO‐CI basis and states to give the correct density for all properties. This should map onto the constrained wave function in the region of the constraint and at the same time minimize the energy of the total molecular wave function. Such a density would be suitable for the density analyses favored by Bader and Nguyen‐Dang [Adv. Quantum Chem. 14, 113 (1981)], Mezey [Theor. Chim. Acta 54, 95 (1980); 58, 309 (1981); 59, 321 (1981)], and March [Theoretical Chemistry (Royal Society of Chemistry, London, 1981), Vol. 4, p. 158], and show the real atom needed to generate the molecule.
Molecular orbital studies on the structure of nucleoside analogs. IV. Conformation of 3‐deazapurine nucleosides
Authors: Saran Anil , Chatterjee C. L.
Published: December 2004

Conformational properties of 3‐deazapurine nucleosides (namely, 3‐deazaadenosine and 3‐deazaguanosine) have been investigated by the PCILO method. Both C(2′)‐endo and C(3′)‐endo sugar puckers have been considered and the results indicate that the conformational preferences of these nucleoside analogs are quite different from those of their parent nucleosides adenosine and guanosine, respectively. This result has been correlated in terms of the biological inactivity of these nucleoside analogs.
On the use of spin graphs for spin adapting many‐body perturbation theory
Authors: Mukhopadhyay Atri
Published: December 2004

In connection with spin adaptation in many‐body perturbation theory, this paper reexamines the use of spin graphs in view of a Hugenholtz‐like representation where both the orbital and the spin parts coexist. Together with the idea of essentially distinct diagrams, this representation leads to an economic handling of spin adaptation. As a side issue, the appropriate generalization of the Epstein–Nesbet partitioning for spin‐adapted perturbation theory is obtained. Compact formulas up to fourth order of the ground‐state energy, and up to third order for excitation energies and ionization potentials are given.
On the unitarily invariant decomposition of Hermitian operators
Authors: Sun Chia‐Chung , Li Xue‐Qui , Tang Au‐Chin
Published: December 2004

The unitarily invariant decomposition of Hermitian operators for a boson system is performed by means of the symmetry of group SO(2, 1) and the decomposition is also closely related with Lie algebra.
Magnetic properties and induced current density in acetylene
Authors: Lazzeretti P. , Rossi E. , Zanasi R.
Published: December 2004

Coupled Hartree–Fock perturbation theory, within the framework of an accurate calculation, has been employed to visualize the electronic current density vector field induced by an external uniform magnetic field in the acetylene molecule. The current regime in a plane containing the molecular axis is rather different from those usually accounted for, evidencing the presence of a toroidal vortex in the CH bond. The maps are useful in rationalizing the experimentally observed proton and carbon NMR chemical shifts.
Usage de l'algkbre de lie su(n) dans l'etude des systèmes quantiques à n etats. III. Définition et obtention des constantes du mouvement conjoncturelles
Authors: Tillieu Jacques , Van Groenendael Augustin
Published: December 2004

A partir de I'opérateur‐densité d'un système quantique à n états, sont définies et calcultes des constantes du mouvement pour lesquelles est proposée I'appellation nouvelle de conjoncturelles. On établit qu'il en existe au maximum n − 1 linéairement indépendantes. A I'aide des sous‐algèbres su(m) (m < n ), on montre comment il est possible d'introduire, suivant la forme de I'hamiltonien, des constantes du mouvement conjoncturelles reliées aux composantes du vecteur de cohérence.
Why is there a molecular relativistic effect?
Authors: Katriel J. , Feller D. , Davidson E. R.
Published: December 2004

The almost exclusive association of the molecular geometry dependence of the relativistic correction with the valence orbital contribution to the mass‐velocity and Darwin terms is investigated using SCF and MCSCF wavefunctions. The requirement of orthogonality of the valence orbitals to the core orbitals is confirmed to be the mechanism responsible for the increase in (the absolute value of) relativistic energy upon decrease of the internuclear distance. Certain “fingerprint”‐type features of the valence relativistic correction, revealing the identity of the particular core orbital giving rise to it, are identified.
Perturbation theory without wave function for multidimensional systems
Authors: Fernández Francisco M. , Castro Eduardo A.
Published: December 2004

A new method to obtain perturbation corrections to the eigenvalues of multidimensional quantummechanical models is developed. It consists of rearranging the Rayleigh‐Schrodinger perturbation theory so that any coefficient of the perturbation series is obtained from a simple and compact recursion relationship. The Zeeman effect in hydrogen and the hydrogen molecule‐ion are used to illustrate the procedure.
Electron‐hole pair excitation in atom‐surface scattering
Authors: Iadonisi Giuseppe , Levi Andrea C.
Published: December 2004

The inelastic scattering of a light atom (helium) from a metallic surface with creation or annihilation of electron‐hole pairs is studied. Diagonal and off‐diagonal matrix elements of the atom‐metal interaction are discussed. The nonadiabatic contributions to the scattering are analyzed in terms of a statistical potential. Explicit calculations are performed for a jellium model at electron densities corresponding to Al and Na. The electron‐hole pair excitation probabilities turn out to be of the order of 10−5–10−3.
Continuum states of the hydrogen molecule with the R‐Matrix method
Authors: Tennyson Jonathan , Noble C. J. , Burke P. G.
Published: December 2004

The interaction of low‐energy electrons with H and ligh with H2 is analyzed using the R‐matrix method including both coupled state and polarization effects ab initio. Particular attention is paid to the energy region containing low‐lying H*2 resonances which converge to H A 2Σ. Resonances in both elastic scattering and the photoionization asymmetry parameter, β, are presented. At low photon eneries, satisfactory results for vibrationally resolved photoionization are obtained using the adiabatic nuclei approximation. The use of nonadiabatic techniques for higher energies is discussed.
Effect of hydrogen chemisorption on the magnetism of nickel clusters
Authors: Fournier R. , Salahub D. R.
Published: December 2004

Results of self‐consistent field, local spin density, scattered wave calculations are reported for nickel clusters of 10, 13, and 14 atoms and these clusters interacting with one or two chemisorbed hydrogen atoms. The pure nickel clusters all have a reasonable average atomic magnetic moment (the average over all the clusters is 0.66µB) and the addition of hydrogen reduces this moment in each case. The reduction of magnetic moment is clearly larger on the nickel atoms that are nearest to hydrogen but there is also a noticeable change in the moments of the other atoms of the clusters. Three factors, of varying importance for the different clusters, contribute to the changes in the overall and local magnetic moments: (i) The extra electron brought in with the hydrogen goes into a down‐spin Ni d level, reducing the moment. (ii) The reelectron duced moment is accompained by a reduced exchange splitting and consequently some up‐spin d electrons, not directly involved in the bonding to hydrogen, are transferred to lower lying down‐spin d orbitals. (iii) For atoms close to the adsorbate, d character in the local density of states is pushed above the Fermi level through antibonding interactions with the hydrogen, further reducing the moments of these atoms.
The formation of Na+ and Na ions from Na*(2P) atoms near a tungsten surface. II. Extended diatomics‐in‐molecules models
Authors: Kuntz P. J.
Published: December 2004

Potential energy surfaces (PES) for Na(2S, 2P) interacting with a tungsten surface partially covered with sodium ions are computed within the framework of the diatomics‐in‐molecules (DIM) method. A small number (1 to 10) of adsorbed sodium atoms are considered explicitly, the effect of the rest being taken into account through the fragment matrix elements in the DIM formulation. A physical model proposed previously to account for the experimental observation of Na+ and Na ions is supported by these calculations and, in addition, a new pathway to Na products is identified. The effect of including extra adsorbed atoms is discussed in terms of the molecular wave functions and a sensitivity analysis.