bluuebunny/crossref_metadata_2025_split huggingface dataset:
Explicitly connected expansion for the average value of an observable in the coupled‐cluster theory
Authors: Jeziorski Bogumił , Moszynski Robert 
Published: January 2005

AbstractAn explicitly connected commutator expansion for the average value of an observable in the coupled‐cluster theory is derived. Specifically, it is shown that the expectation value of an operator for the state Ψ, related to the Fermi vacuum Φ by the exponential Ansatz ψ = eT Φ, is expressed as a finite commutator series containing the cluster operator T and an auxiliary operator S, defined by a linear equation involving again a finite commutator series in T. The above result is applied to derive the explicitly connected commutator form of the order‐by‐order many‐body perturbation theory (MBPT) expansion for the expectation values and density matrices. We also show how the commutator expansion derived by us can be used as a basis for size‐extensive infinite‐order summation techniques. An operator technique of eliminating the nonlocal, “off‐energy shell” denominators from MBPT expressions is proposed and applied to obtain compact commutator formulas for the expectation values of one‐ and two‐electron operators through the fourth and third order, respectively, and for the correlation energy through the fifth order of perturbation theory. © 1993 John Wiley & Sons, Inc.
A first‐principles approach to high‐Tc superconductivity. I. A consistent one‐electron theory of the N‐electron problem
Authors: Fritsche L. 
Published: January 2005

AbstractWe review and update a recently developed one‐particle theory of N‐electron systems that bears a certain resemblance to density functional (DF) theory and has been put forward by the present author. As distinct from DF theory, the new one‐particle scheme applies to any N‐electron eigenstate including the ground state. For the latter case, the key equations become identical to those familiar from the Kohn–Sham version of DF theory. The theory given here constitutes the basis for a consistent treatment of normal conductivity and superconductivity, which will be discussed in Part II of this article. © 1993 John Wiley & Sons, Inc.
Finding transition states when second‐order Jahn–Teller instability occurs
Authors: Simons Jack 
Published: January 2005

AbstractWhen second‐order Jahn–Teller couplings become strong along “streambeds” on potential energy surfaces, instability reflected in negative curvature along a symmetry‐lowering distortion coordinate can take place. The point where such negative curvature sets in is usually not a transition state because the gradient of the potential is usually large there. In this paper, it is demonstrated how to use the local energy, local gradient, local Hessian, and knowledge of how quickly the curvature for the symmetry‐breaking mode evolves along the streambed (i.e., the derivative of this curvature) to predict how far to move in the symmetry‐breaking mode in search of the desired transition state. It is shown that the Hessian matrix evaluated at the symmetry‐broken geometry suggested by this analysis has only one negative eigenvalue. Because this analysis is based on a local approximation to the potential, its predictions are, of course, approximate. As such, they only “suggest” the proper direction and magnitude that one should “step” to move toward a transition state. © 1993 John Wiley & Sons, Inc.
Ground and first excited states of fractionally charged sodium atoms
Authors: Pavão A. C. , Craw John Simon , Nascimento Marco Antonio Chaer 
Published: January 2005

AbstractThe energy levels in sodium atoms with quarks attached to the nucleus are obtained using the configuration interaction method. It is found that the calculated 3p (2P) → 3s (2S) electronic transition in the Na−1/3 quark–atom system is in agreement with that predicted by extrapolation of experimental data. Also, ionization potentials of fractionally charged sodium atoms are discussed. © 1993 John Wiley & Sons, Inc.
Some remarks on the resemblance theorems associated with various orthonormalization procedures
Authors: Löwdin Per‐Olov 
Published: January 2005

AbstractA survey is given of the resemblance theorems associated with various types of orthonormalization procedures having different kinds of symmetry properties appearing in the current literature. It is shown that the proofs for the minimum properties are closely connected with the fact that the Hilbert–Schmidt norm of an operator is always nonnegative and has the lowest value equal to zero. © 1993 John Wiley & Sons, Inc.
Electric‐field mapping of some anions and cations of adenine and guanine
Authors: Mohan C. G. , Kumar Anil , Mishra P. C. 
Published: January 2005

AbstractElectric‐field maps of certain anions and cations of adenine and guanine have been studied. The results are compared with those of neutral adenine and guanine. In all cases, the geometries were fully optimized using the MNDO molecular orbital method and the fields were computed using Mulliken charges. Reactivities and hydrogen‐bonding pattern predicted by electric fields, including those of cations, are in satisfactory agreement with experiment. © 1993 John Wiley & Sons, Inc.
Multiplication theorems for orthogonal polynomials
Authors: Kleindienst H. , Lüchow A. 
Published: January 2005

AbstractIn this paper, a general method is presented that allows the derivation of the expansion coefficients of the product of two orthogonal functions provided the generating function is known. For the three classical orthogonal polynomials, the Laguerre, the Hermite, and the Legendre polynomials, the coefficients blmn with ϕmϕn = ∑lblmnϕl are derived. © 1993 John Wiley & Sons, Inc.
Perturbation theory to determine the stable isomer of triatomic linear molecules
Authors: Su Ming‐Der 
Published: January 2005

AbstractThe electronegativity perturbation theory up to the fourth order has been used to study the preferred isomer of linear triatomic molecules. Systems with 10–16 valence–electron systems are discussed and our results are in good agreement with the experiment. The only exception is the isomers of PNO. The usefulness of the perturbation theory is briefly discussed. © 1993 John Wiley & Sons, Inc.
Recurrence relations for the evaluation of electron repulsion integrals over spherical Gaussian functions
Authors: Fortunelli Alessandro , Salvetti Oriano 
Published: January 2005

AbstractRecurrence relations are derived for the evaluation of two‐electron repulsion integrals (ERIs) over Hermite and spherical Gaussian functions. Through such relations, a generic ERI or ERI derivative may be reduced to “basic” integrals, i.e., true and auxiliary integrals involving only zero angular momentum functions. Extensive use is made of differential operators, in particular, of the spherical tensor gradient 𝒴(∇). Spherical Gaussians, being nonseparable in the x, y, and z coordinates, were not included in previous formulations. The advantages of using spherical Gaussians instead of Cartesian or Hermite Gaussians are briefly discussed. © 1993 John Wiley & Sons, Inc.
Semiempirical evaluation for proton affinities of phosphorus compounds
Authors: Pierini Adriana B. , Duca José S. 
Published: January 2005

AbstractWe here report the AM1 and PM3 evaluation of proton affinities for phosphorus compounds. The substituent effects, the preferred site of protonation, and the geometry changes produced upon protonation are discussed in terms of the present semiempirical calculations that are compared with experimental data and previous ab initio results. © 1993 John Wiley & Sons, Inc.
Molecular calculations using space‐restricted basis functions
Authors: Goodfriend P. L. , Tsonchev S. I. 
Published: January 2005

AbstractMolecular calculations are presented using “space‐restricted basis functions,” i.e., basis functions that are nonzero only in selected regions of space. The nature of the calculations their justification, and their possible utility to quantum chemistry are described. © 1993 John Wiley & Sons, Inc.
Some comments on the counterpoise correction for the basis set superposition error at the correlated level
Authors: Cook D .B. , Sordo J. A. , Sordo T. L. 
Published: January 2005

AbstractThe use of the counterpoise method for the mitigation of basis set superposition error at the correlated level is discussed. Evidence is presented to show that the ghost basis plays a dual role in the counterpoise method: The orbitals of the system are improved by the ghost basis but at the expense of a nonphysical increase in the dimension of the virtual space. This second factor has no effect on application of the counterpoise method at the SCF level but it makes the use of the counterpoise method at the correlated level much less straightforward. © 1993 John Wiley & Sons, Inc.
Some convergence aspects of the one‐center expansion methods
Authors: Bouferguene A. , Fares M. 
Published: January 2005

AbstractAmong the methods that may be used to carry out multicenter integrals over STOS, the one‐center two‐range expansion is probably the oldest one. However, the convergence of the leading series is generally slow and, hence, time‐consuming. Therefore, it was the aim of the present work to show that the so‐called nonlinear sequence transformations may be of substantial help for improving the rate of convergence of such series. © 1994 John Wiley & Sons, Inc.
Numerical procedures in electrochemical simulation
Authors: Cecilia Joan , Galceran Josep , Salvador José , Puy Jaume , Mas Francesc 
Published: January 2005

AbstractThe use of both the Laplace transformation technique and the finite element method has been analyzed in an electrochemical system. The diffusion‐controlled adsorption process of a species onto an electrode surface is studied in detail. © 1994 John Wiley & Sons, Inc.
Self‐consistent second‐order screening in many‐body theory
Authors: Van doren V. E. , Van camp P. E. , Straub G. 
Published: January 2005

AbstractSelf‐consistent screening arises in all many‐body problems where one‐particle equations containing functionals of the solutions are considered. In the theory of simple metals, e.g., these one‐particle equations are usually solved to second‐order perturbation in the crystal pseudopotential and to first order in the screening. However, higher‐order screening terms have a sizable effect on the form factors, the electron charge density, and the screened pseudopotential. The effects of second order are presented for the bcc simple metals Na and Ba. A nonlocal exchange‐correlation potential has been used since local density approximations such as ρ1/3 cause difficulties in the electron–electron dielectric function. © 1994 John Wiley & Sons, Inc.
Orbitals expanded in slater functions with single‐exponent by shell and by subshell
Authors: Garcia De La Vega J. M. , Miguel B. 
Published: January 2005

AbstractSlater‐type orbitals (STOs) with a single‐exponent by shell or by subshell have been constructed to reduce the number of integrals evaluated in the electronic calculations. The expansion of orbitals in these new basis sets has been carried out in detail for the ground state of the Ne atom. We have carried out a study of STO basis sets with a different size for this atom that could help to propose empirical rules for the selection of these basis sets for other atoms. The usefulness of STOs with single‐exponent by shell and subshell and the splitting of s and p functions are discussed. © 1994 John Wiley & Sons, Inc.
Developments in multicenter molecular integrals over STOs using expansions in spherical harmonics
Authors: Jones Herbert W. 
Published: January 2005

AbstractThe strategy of using expansions in spherical harmonics of displaced Slater‐type orbitals for the evaluation of multicenter molecular integrals is reviewed and projected. Our Löwdin α–function method is augmented by computer algebra and C, E, and F matrices with rational elements. This permits exact evaluations of each term in an infinite sum using a commercial computer algebra program to investigate the three‐center nuclear attraction integral. Each term (harmonic potential) is important for proposed use in numerical evaluations of multicenter integrals. © 1994 John Wiley & Sons, Inc.
A new model of a molecule based on the soft body
Authors: Konarski J. 
Published: January 2005

AbstractThe basic idea of the deformable or soft‐body model of a molecule, which starts from a new definition of the reference configuration, is presented. It is shown that this model introduces into the Hamiltonian a new part that describes deformation energy of a molecule brought about by its rotation. This part leads to nonlinear terms, whose numerical values were compared with the semiempirical approach. © 1994 John Wiley & Sons, Inc.
Theory of the expansion of wave functions in a gaussian basis
Authors: Kutzelnigg Werner 
Published: January 2005

AbstractThe convergence properties of the expansions of (a) the function 1/r and (b) the function exp(‐αr) in an even‐tempered basis of Gaussians are studied analytically. The starting points are the Gaussian integral representations of 1/r and exp(−αr). One arrives at an expansion in a finite number of Gaussians in three steps: (1) a restriction of the integration domain, (2) a variable transformation, and (3) discretization of the integral. The cutoff error goes in both cases essentially as exp(−ah), and the discretization error, as exp(−b/h). The minimum overall error is reached for the β‐parameter of an even‐tempered basis β ∽ exp(c/√n), where n is the dimension of the basis, and the error itself decreases as ϵ ∽ exp(−d√n). Different optimum basis parameters are obtained depending on which quantity one wants to minimize, e.g., the error of the energy expectation value, the distance in Hilbert space, the variance of the energy, or the density at the nucleus. © 1994 John Wiley & Sons, Inc.
Quantum phase‐space densities for a quartic oscillator
Authors: De Polavieja G. G. , Borondo F. , Benito R. M. 
Published: January 2005

AbstractA quantum analog to the classical Poincaré surface of section, based on the Husimi function, is calculated for the quartic oscillator: H = 1/2(P + P) + x2y2/2 + α(x4 + y4). The corresponding quantum densities in phase space are analyzed, and they show certain localization properties for a large number of states. © 1994 John Wiley & Sons, Inc.
Functional derivative δE/δρ in calculation of chemical potential for the Kohn–Sham electronic system
Authors: Tkacz‐śsamiech Katarzyna , Ptak W. S. , Koleżyński A. , Mrugalski J. 
Published: January 2005

AbstractA method for finding the chemical potential for an electronic system with density ρ = Σρi represented within the Kohn–Sham approximation is proposed. To find the chemical potential of the system under consideration, we propose to refer to the definition μ = δE/δρ and to apply the mathematical properties of functional derivatives. Particularly, in the case examined, the result μ = μ(r) ≠ const has been obtained, which may be explained in the framework of the calculus of variation. Taking the limit limr→∞ μ(r) as the best approximation to the proper equilibrium chemical potential of a free atom, one obtains μ = −I, where I denotes first ionization energy. A possibility of further applications of the proposed method in relation to crystalline systems is also discussed. © 1994 John Wiley & Sons, Inc.
Computation of algebraic formulas for wigner 3‐j, 6‐j, and 9‐j symbols by maple
Authors: Lai Shan‐Tao 
Published: January 2005

AbstractThree programs capable of computing algebraic formulas for Wigner 3‐j, 6‐j, and 9‐j symbols have been written in the Maple* program language. These programs can also compute numerically exact values of 3‐j, 6‐j, and 9‐j symbols. © 1994 John Wiley & Sons, Inc.
Path integral's semiclassical quantification
Authors: Marañtón Julio 
Published: January 2005

AbstractWe discuss here a new formal way to evaluate the electronic correlation energy of a molecular system. We use the path integral formalism in the regime of the molecular orbitals. The semiclassical approximation in this procedure is an expansion of the effective action Seff around the classical closed orbits into generalized phase space keeping only the quadratic fluctuation. Thus, after some transformations, we apply to the final expression analogous conditions to the Bohr‐Sommerfeld quantification rules. © 1994 John Wiley & Sons, Inc.
Potential‐barrier model at metal surfaces: Thin films and its dependence on the film thickness
Authors: Mola E. E. , Paola C. A. , Vicente J. L. 
Published: January 2005

AbstractWe propose a model for the potential of thin metal films, in which (1) we reproduce self‐consistent effective potentials (i.e., Lang and Kohn), in fact, better than any approximation in the existing literature, (2) we parameterize the potential as a function of the film thickness, and (3) we approach the classical image potential for large separation from the surfaces. Our potential does not diverge as the electron approaches the surfaces and takes into account the effect of the two surfaces. It reproduces the first peak in the effective potential, which is a Friedel oscillation. We present a simple dependence of the potential with the film thickness that (1) allows a direct description of the quantum size effects and (2) shows how the bulk surface potential is reached. This makes our model useful in the interpretation of tunnel experiments, field emission, and scanning tunneling microscopy. © 1994 John Wiley & Sons, Inc.
Theoretical conformational study of the stabilities and geometries of [2,2] (2,7)naphthalenophane‐1,11‐diene and related compounds
Authors: Rioseras‐garcia Ma. J. , Hernando‐huelmo J. Ma. 
Published: January 2005

AbstractThis theoretical study was to determine the relative stability of the different species proposed experimentally and to establish which of the two pathways suggested is the most probable. A conformational study of the geometries of the stable compounds has been carried out using the semiempirical quantum mechanic method AM1. © 1994 John Wiley & Sons, Inc.
Electronic structure and optical properties of a tin‐encapsulated nickel porphyrazine compound
Authors: Liang X. L. , Ellis D. E. , Gubanova O. V. , Hoffman B. M. , Musselman R. L. 
Published: January 2005

AbstractThe recently synthesized metal‐encapsulated porphyrazine compound, [Sn(t‐Bu)2]4‐star‐Ni(porphyrazine)‐S8, shows very interesting structural and optical absorption features compared with other metal‐centered porphyrazines, e.g., metal phthalocyanines (Pc). Using self‐consistent‐field local density theory, we studied the ground‐state and excited‐state electronic structure of this molecule and compared it with its metal phthalocyanine analog NiPc. The theoretical optical spectra including oscillator strengths are in good agreement with experimental absorption and show that the characteristic transitions at the so‐called Soret band in NiPc are red‐shifted in the new compound. © 1994 John Wiley & Sons, Inc.
Comparison of quantum mechanical methods to compute the biologically relevant reactivities of cyclopenta‐polycyclic aromatic hydrocarbons
Authors: Rabinowitz James R. , Little Stephen B. 
Published: January 2005

AbstractIn computational studies to understand the interaction of polycyclic aromatic hydrocarbons (PAHs) with biomolecular systems, the semiempirical method AM1 has been used previously to determine the geometry of the PAH and its metabolites and relevant intermediates. A number of studies have shown that AM1 provides geometries for parent PAHs that are acceptably close to experimentally determined structures. However, many of the properties that determine the manner by which PAHs interact with biological nucleophiles depend on the structure of metabolites and reactive intermediates where less experimental information is available. In a previous study, we used AM1 to obtain the molecular geometries of reactive intermediates of cyclopenta‐PAHs (cPAHs) and then used single‐point Hartree‐Fock calculations, with the gaussian 3‐21g basis set, to obtain molecular energies and charge distributions, in order to predict the direction of epoxide ring opening. Recent advances in the availability of computational hardware and software have provided other, more rigorous, methods for approaching this problem. In this study, we used hartree‐fock methods in the gaussian series of programs employing the 3‐21g and 6‐31g basis sets and the local density functional method Dmol to obtain molecular geometries, energies, and charge distributions of the epoxides and the two potential hydroxycarbocations that could result from protonated ring opening, for a series of cPAHs. We have also performed the same calculations with AMSOL/SM2, a semiempirical method that adds the effect of the aqueous environment to the AM1 Hamiltonian. The division of the cPAHs into classes is not altered by these more rigorous calculations. The inclusion of water in the Hamiltonian has a greater effect on the results than using the ab initio methods to obtain the structure. © 1994 John Wiley & Sons, Inc.
An analysis of nonlocal density functionals in chemical bonding
Authors: Leeuwen Robert Van , Baerends Evert Jan 
Published: January 2005

AbstractIn this work, we carry out an analysis of the gradient‐corrected density functionals in molecules that are used in the Kohn–Sham density functional approach. We concentrate on the special features of the exchange and correlation energy densities and exchange and correlation potentials in the bond region. By comparing to the exact Kohn–Sham potential, it is shown that the gradient‐corrected potentials build in the required peak in the bond midplane, but not completely correctly. The gradient‐corrected potentials also exhibit wrong asymptotic behavior. Contributions from different regions of space (notably bond and outer regions) to nonlocal bonding energy contributions are investigated by integrating the exchange and correlation energy densities in various spatial regions. This provides an explanation of why the gradient corrections reduce the local density approximation (LDA) overbinding of molecules. It explains the success of the presently used nonlocal corrections, although it is possible that there is a cancellation of errors, too much repulsion being derived from the bond region and too little from the outer region. © John Wiley & Sons, Inc.
A mass formula for the energy of metal clusters
Authors: Mañanes A. , Membrado M. , Pacheco A. F. , Sañudo J. , Balbás L. C. 
Published: January 2005

AbstractWe obtain an analytic expression for the total energy of a metallic cluster formed by N atoms of valence v and with net charge Q, by solving variationally the extended Thomas–Fermi version of density functional theory within the spherical jellium model. The energy is expressed as an expansion (mass formula) in decreasing powers of the cluster radius RI = rsZ1/3, with Z = vN, and rs, the one electron radius of the bulk,

and the coefficients of this mass formula are functions of rs. Contributions of volume (RI3), surface (RI2), curvature (RI), constant (RI0), (1/RI), and (1/RI2) are clearly separated in the formula. The Chemical potential, work function, electron affinity, and ionization potential are easily obtained for neutral and charged clusters of any electronic density in the metallic range. A general estimation of the critical size for stability against electron detachment of negatively charged clusters is also obtained. The stability of highly charged clusters against fragmentation is also studied. © John Wiley & Sons, Inc.