bluuebunny/crossref_metadata_2025 huggingface dataset:
Relativistically parametrized extended‐Hückel calculations. II. Orbital energies of group‐IV tetrahalides and tetramethyls
Authors: Lohr L. L. , Hotokka M. , Pyykkö P.
Published: December 2004

Relativistically parametrized extended‐Hückel (REX) calculations are reported for MX4 (M = Ti, Zr, Hf, C, Si, Ge, Sn, Pb; X = Cl, Br, I) and for M(CH3)4 (M = Ti, C, Si, Ge, Sn, Pb). Satisfactory agreement is obtained with experiment and with earlier assignments both for the energy levels and for their relativistic splittings. This encourages the use of REX for assigning PES spectra. Double‐ζ radial functions (REX and EHT) are given for Cl, Br, and I.
QCLDB—Quantum chemistry literature data base—a trial
Authors: Osamura Y. , Yamabe S. , Hirota F. , Hosoya H. , Iwata S. , Kashiwagi H. , Morokuma K. , Togasi M. , Obara S. , Tanaka K. , Ohno K.
Published: December 2004

A brief account of a quantum chemistry literature data base (QCLDB) is described, which contains the key information of about 2000 papers of ab initio calculations of atoms and molecules published in 1977–1979. The QCLDB is stored in a computer and can be sorted and rearranged into author and substance indices. Selection of the items for each paper in a computer‐readable data base is discussed.
Purine–water interactions in base stacking
Authors: Langlet J. , Giessner‐Prettre C. , Pullman B. , Claverie P. , Piazzola D.
Published: December 2004

The intermolecular energy of two conformations of stacked hydrated purine dimers is computed for a varying number of molecules of water around the stacks. The results obtained show that hydration can modify the relative stability of the dimers as calculated in vacuo. In addition, the optimized arrangements of the molecules of water around the dimers depict that purine molecules strongly interact with the solvent and that bridges made of water dimers or trimers are formed between the stacked bases.
Quasirelativistic MO calculations on platinum complexes (anticancer drugs) and their interaction with DNA
Authors: Boudreaux E. A. , Carsey T. P.
Published: December 2004

A self‐consistent modified extended Hückel (SC‐MEH) MO method has been extended to study the electronic structure and bonding in the complex ions: PtC42−, Pt(NH3)42+, cis‐Pt(NH3)2Cl2, trans‐Pt(NH3)2Cl2, and Pt(CN)42−, in which the atomic basis functions were derived from the published relativistic Dirac‐Fock functions. Both quasirelativistic (in the frozen spin approximation) and nonrelativistic calculations were made to include the 5s 5p 5d 6s and 6p levels of Pt and the nsnp valence levels of the ligands. Similar calculations have been completed in the nonrelativistic mode for Pt(NH3)2 (OH2)L and Pt(NH3)2L2, where L is the monodentated bond at the N‐7 position of guanine in DNA and L2 are the bidentated bonds at the N‐7 and O‐6 guanine sites, respectively. Based on these initial results specific conclusions have been made regarding a proposed biochemical mechanism that has been advanced to explain the unique anticancer activity of cis‐Pt(NH3)2 Cl2 (DDP).
Mechanism of binding of iron to potential therapeutic chelating agents
Authors: Spingarn Neil E. , Sartorelli Alan C.
Published: December 2004

To aid in designing new therapeutic iron chelating agents, the mechanism of iron binding to prototypic heterocyclic carboxaldehyde thiosemicarbazones has been studied. Based on molecular orbital and spectroscopic studies, iron (II) is found to bind in a covalent manner, while iron(III) seems to interact ionically. However, with both iron(II) and iron(III), chelate formation is dependent on charge interaction between the metal and the coordinating atoms of the ligand.
β−‐Decay effect on the proton movement in the pyridine–pyrrole hydrogen‐bonded system
Authors: Ikuta Shigeru , Hashimoto Shuichi , Imamura Masashi
Published: December 2004

The potential‐energy curves for the movement of proton along the hydrogen‐bond direction were calculated for the parent and cations produced from the β− decay of pyridine‐pyrrole labeled by tritium (3H) or carbon‐14(14C). For all cations the double minimum potential is predicted to be formed, and the activation energy for the proton transfer from one well to the other is about 10.0 kcal/mol, which is much lower than that in the (NH2HNH2)+ ion. A positional effect of nuclear transformation is scarcely expected in 3H β− decay, whereas a slight positional effect may be expected in 14C β− decay.
Electronic states near dislocations in transition metals: An application of quantum chemistry in technology
Authors: De Hosson J. Th. M.
Published: December 2004

This paper outlines a model for calculating the localized states of a 〈 100 〈 edge dislocation in α‐Fe. The model used for the calculations is based on the multiple‐scattering model (SCF‐X α‐SW). The purpose of this research is twofold: (1) To determine changes in electronic structure of the lattice near the core region of defects in α‐Fe. (2) The variations of hydrostatic pressure about an edge dislocation produce a rearrangement of the conduction electrons. The question is what electrical interaction might be expected between a dislocation and a charged solute atom. The calculations show that the electrons tend to flow away from the compression side toward the dilated regions. The electrical contribution to the binding energy of a solute atom and a dislocation in α‐Fe is of the order of 0.01 Ry/electronic unit charge of the atom.
Lattice relaxation and electric‐field‐gradient calculations in impurity‐doped single ionic crystals
Authors: Satoh Mitsuo , Taki Toshihiko
Published: December 2004

The lattice‐relaxation parameters in several ionic crystals doped with monovalent impurity ions are calculated by energy minimization, taking into account the Coulomb, overlap‐repulsive, and three‐body potential energies. The displaced 256 ions around one substitutional impurity ion are taken into consideration and the results are utilized to calculate the electric‐field gradients at sites similar to the (1,0,0), (1,1,0), and (1,1,1) sites relative to the impurity at (0,0,0), by using two different models for three‐body potentials.
Rotational tunneling of methane on the surface of graphite
Authors: Nosé Shuichi , Ozaki Yoshiaki , Maki Kazuo , Kataoka Yosuke
Published: December 2004

Neutron scattering spectra from methane molecules adsorbed on a surface of graphite were observed by Newbery et al. They found four inelastic peaks in the temperature range lower than 30°K and assigned them to transitions between rotational tunneling states of methane molecules. This system was investigated by introducing both the interaction between methane molecules and that between a methane molecule and carbon atoms of graphite in order to explain the observed spectrum. It is shown that the system can be analyzed in terms of an effective field with tetrahedral symmetry.
Uniform quality gaussian basis sets for molecular calculations, I. C1 hydrocarbons
Authors: Poirier R. A. , Daudel R. , Mezey P. G. , Csizmadia I. G.
Published: December 2004

The optimality of MO basis sets of Gaussian functions, when constructed from AO basis sets optimized for the neutral atom or for atom ions, is investigated. A formal charge parameter Q is defined and used to adjust the AO basis sets to the molecular environment, by virtue of a simple quadratic expression. Calculations on a series of C1 hydrocarbons (CH2, CH3, CH3+, CH3−, CH4) using 3G basis sets indicate considerable variations in the optimum Q value with the molecular species. The proposed method offers a simple alternative technique to a full molecular basis set optimization.
Uniform quality gaussian basis sets for molecular calculations. II. C2 hydrocarbons
Authors: Poirier R. A. , Daudel R. , Csizmadia I. G.
Published: December 2004

This investigation is a continuation of a study on the optimality of MO basis sets of Gaussian functions, when constructed from AO basis sets optimized for the neutral atom or for ions. A formal charge parameter Q is used to adjust AO basis sets to the molecular environment, by virtue of a simple quadratic equation. Calculations are performed on a series of seven C2 hydrocarbons (C2H2, C2H4, C2H6, C2H3+ (open), C2H3+ (bridged), C2H5+ (bridged), and C2H4− radical anion). A simple rule is formulated to give approximate values of the charge parameter Q.
One‐ and two‐particle fractional parentage for arbitrary point groups, configurations, and coupling schemes
Authors: Fieck Gerhard , Wirsich Joachim
Published: December 2004

The fractional parentage coefficients (CFPS) for arbitrary symmetry (including non‐simply reducible point groups), different coupling schemes, and several open shells are discussed with emphasis on the common features. The differences between the coupling schemes arise merely from a different interpretation of the relevant symmetry group. The formulation uses the particle‐number representation (so‐called second quantization), in which the CFPS appear as the reduced matrix elements of the creation or annihilation operators. This shows, that there is no principal difference in the fractional parentage scheme of one or several open shells. For the latter case the theory of adjective CFPS is worked out and applied to an example of octahedral symmetry.
Electrostatic interaction for arbitrary point groups, configurations, and coupling schemes
Authors: Fieck Gerhard , Wirsich Joachim
Published: December 2004

The electrostatic interaction for arbitrary symmetry (including non‐simply reducible point groups), different coupling schemes, and several open shells is discussed from a common viewpoint using the particle‐number representation (second quantization). The different coupling schemes simply arise from a different interpretation of the relevant symmetry group. Using the adjective CFPS of the preceding paper, the interaction within several open shells can be calculated. In the case of one‐center expansions like ligand field theory the many‐particle matrix elements are directly expressed by the radial Slater integrals using isoscalar factors. An example of the formalism is worked out. By the way the unitary transformations between strong and weak field coupling schemes are expressed recursively in the number of particles.
Hypevirial theorem for open dynamical assemblies in the density matrix representation
Authors: Schweitz Jan‐Åke
Published: December 2004

The concepts of “open assembly” is defined, and the hypervirial theorem is derived in three steps: (i) An equation of motion of the reduced density matrix of the first order is derived. (ii) This equation is utilized to derive a general equation of continuity for single‐particle properties. (iii) The hypervirial equation for open assemblies is obtained as a long‐time average of the continuity equation. The hypervirial theorem is shown to be equivalent to a simple postulate: no physical property can keep on accumulating for ever in a limited volume. Finally, the hypervirial theorem is applied to the problems of force, torque, and virial balance in open dynamical assemblies, and the results are compared with the corresponding classical results.
Variational constraints on perturbed eigenvalues and their perturbation expansions. II. Perturbational inequalities
Authors: Silverman Jeremiah N.
Published: December 2004

A large family of interlocking perturbational inequalities is derived by variational considerations for the stationary states of all systems described by a Hamiltonian linear in a real perturbing parameter λ. These inequalities constrain in many different ways the perturbation expansions of both exact and variational eigenvalues for these systems; analogous inequalities are derived for the components of the eigenvalues. A special feature of the analysis consists of obtaining inequalities applicable to the separate sums of even‐ and odd‐order perturbation energies. For lowest states of each symmetry and for positive definite perturbing operator, the interlocking effect of the inequalities becomes extremely restrictive. The inequalities are illustrated with several numerical calculations for different systems and states of the helium isoelectronic sequence. The direction of the inequalities is found to be unaffected by low‐order truncation, thus rendering them applicable to low‐order perturbation expansions. The inequalities are used to study the efficacy of low‐order perturbation theory for two‐ to ten‐electron atomic isoelectronic sequences, and to determine the functional dependence upon λ of the eigenvalues and their components for arbitrary atomic isoelectronic sequences.
Axial gaussian‐lobe orbitals: Optimization of highly angularly dependent functions
Authors: Le Rouzo H.
Published: December 2004

Highly angularly dependent axial Gaussian‐lobe orbitals (AGLO) (up to L = 5) are presented. The angular and radial optimizations of these functions have been realized on the ground of theoretical frameworks, previously reported in the literature and somewhat extended here. The numerical difficulties that can appear in the recombination of elementary integrals over lobes are particularly investigated. It is shown that it is necessary to limit the angular accuracy, i.e., the relevant YLo character, in order to preserve the accuracy of atomic integrals. The proposed p, d, f, g, and h AGLOS satisfy this condition, and can be used with confidence in LCAO–MO–SCF calculations. Their advantages, e.g., for the treatment of large symmetrical inorganic systems containing transition metal atoms, are emphasized.
Molecular properties and basis set quality: An approach based on information theory
Authors: Maroulis G. , Sana M. , Leroy G.
Published: December 2004

Information theory can be used to evaluate the quality of a wave function by considering its ability to give values for some observables as close as possible to the experimental ones. A new method for improving the quality of a wave function is proposed. This paper deals exclusively with the HF (X 1∑+) molecule.
Combination of pseudopotentials and density functionals
Authors: Preuss H. , Stoll H. , Wedig U. , Krüger Th.
Published: December 2004

Semilocal pseudopotentials have been determined for first–row (Li to Ne), second row (Na to Ar), and third‐row atoms (K, Ca). Core–valence correlation is included by adjusting the pseudopotentials to experimental energies of ions with a single valence electron. Correlation within the valence shell is taken into account by using the spin–density functional formalism. The approximations involved in this approach are tested for atomic ionization energies as well as binding energies of monohydrides and alkali diatomics, agreement with experiment is usually satisfactory, but in certain applications density functionals should be already included in the fitting of the local part of the pseudopotential. In addition, 3s/3p and 3s/2p basis sets (for first and second row, respectively), designed for use in connection with our pseudopotentials, are given; it is shown that they yield reasonable results for both SCF and correlation energies.
Unitary transformations with the unitary operators depending on projection operators
Authors: Stepanov N. F.
Published: December 2004

Unitary transformations of operators and variables are considered for those cases when a Hermitian operator in the expression U = exp (iS) explicitly depends on the projection operators. Some simple examples of such transformations are given and the equations obtained which define projectors (among special sets of them), thus bringing forth better estimations for upper and lower bounds. The unitary transformations are also applied to the reduced resolvent operator and equations are presented for the operators U that minimize the energy functional.
Multichannel quantization and the static stark effect
Authors: Atabek O. , Lefebvre R.
Published: December 2004

A coupled channel formulation for the static Stark effect on the hydrogen atom is used to obtain directly the complex resonance energies through an iterative matching procedure. The formulation makes use of a complex coordinate. This solves the initialization problem in a very simple way, since the boundary conditions can be those used for bound states. A comparison is made with the results of Reinhardt and collaborators who expand the complex rotated resonance wave function in a basis of integrable functions.
Algebraic characterization of bridged polycyclic compounds
Authors: Mekenyan Ov. , Bonchev D. , Trinajstić N.
Published: December 2004

An approach based on the topological distance matrix is used for algebraic characterization of bridged polycyclic compounds. The classical bridged structures which have external bridges between cycles were examined together with the more complicated three‐dimensional polycyclic systems regarded as containing internal bridges. Thirteen rules are given for characterizing the main types of structural rearrangements in these compounds. The important topological characteristic of (poly)cyclic systems, the molecular cyclicity, is examined in the polycyclic condensed, spiro‐ and bridged structures, respectively.
Effect of molecular size on carbonic anhydrase inhibition by sulfonamides
Authors: Kumar Kamal , Bindal Mahesh C. , Singh Prithvi , Gupta Satya P.
Published: December 2004

The molecular size is found to play an important role in carbonic anhydrase (CA) inhibition by sulfonamides. Significant correlation is obtained between the inhibitory power of meta‐substituted analogs and the van der Waals volume (Vw) of the substitutents. This provides a theoretical basis to map the active sites in enzyme and find the nature of sulfonamide‐receptor binding. It is inferred that in addition to well known binding of sulfamyl group with Zn2+ ion of the enzyme, the meta substituent of sulfonamides interacts with some secondary binding site and this interaction is argued to be of van der Waals type.
Specificity and molecular mechanism of abortificient action of prostaglandins
Authors: Kothekar V.
Published: December 2004

The paper reports comparison of electrostatic charge and energy distribution on the basis of the CNDO/2 method for six forms of prostaglandins–PGF2α, PGF1β, PGE1, PGE2, PGB1, and PGA1–having diverse physiological action. The isopotential mapping done in three dimension showed that the lower value of electrostatic potential and proximity of the two low energy regions around O9 and O11 in PGE2 and PGF2α is probably responsible for their higher abortificient activity. We also compare here the variation of the long‐ and short‐range interaction between ring–chain and chain–chain portion of different forms and compared them with the variation in their action.
Ab initioSCF study of guanidine and substituted guanidines
Authors: Sapse Anne Marie , Snyder Grace , Santoro Angelo V.
Published: December 2004

Proton affinities, geometries with optimized parameters, and net atomic charges are reported for guanidine‐, methyl‐, amino‐, and fluoro‐substituted guanidines. The results are obtained using the ab initio SCF method as implemented by the GAUSSIAN‐70 computer program with a 6–31G basis set. Basicity is discussed in terms of electron distribution and intramolecular attraction forces.
Proton transference in hydrogen bonded systems. I. Uracil tautomerism
Authors: Mondragón A. , Blake I. Ortega
Published: December 2004

We have made a detailed analysis of the adequacy of different theoretical approaches to the study of uracil tautomerism. We have considered the effect of molecular relaxation and the ability of several methods to reproduce it. We have also considered their performance in predicting the tautomerization energy barrier. We found that semiempirical methods are not adequate for predicting the energy value but that they can be used for obtaining geometry optimizations. We also found a strong discrepancy between the energy values predicted by a minimal basis set and a 2ζ basis set, the last one being 24.9 kcal/mol. The implications of these findings are discussed and the results compared with experimental evidence.
Level set topology of the nuclear charge space and the electronic energy functional
Authors: Mezey Paul G.
Published: December 2004

Electronic energy level set topologies in the abstract nuclear charge space Z of molecular systems are defined and analyzed. Two theorems, one on the general convexity of level sets in Z, another on homotopies of boundaries of level sets, induced by nuclear geometry variations in the nuclear configuration space R, are proven. The applications of the two theorems are illustrated by examples of various molecules and ions.
“Stable” quasistationary state: New solution of the time‐dependent Schrödinger equation
Authors: Tachibana Akitomo
Published: December 2004

The new concept of the stability of the quantum mechanical state is introduced for the study of the time‐dependent process of the quasistationary state. A stable solution of the time‐dependent Schrodinger equation predicts the presence of the new sharply localized long‐living state at the most repulsive part of the effective potential.
Evaluation of the second‐order reduced density matrix for correlated electronic wave functions
Authors: Luken William L.
Published: December 2004

Formulas are presented for the evaluation of the second‐order reduced density matrix for correlated wave functions, including wave functions constructed from pairwise nonorthogonal orbitals. Numerical results are provided for the correlation holes and conditional nuclear spin densities for the water molecule.
Conformational analysis by bond orbitals with delocalization corrections: Rotation of the ser‐195 side chain in α‐chymotrypsin
Authors: Surján Peter R. , Náray‐Szabó Gábor , Mayer István
Published: December 2004

A recently developed procedure for calculation of tails of localized molecular orbitals is applied in order to obtain approximate rotational potential curves. In order to calculate reliable rotational barriers, tails, originating from direct interactions between bonding and antibonding strictly localized orthogonal orbitals, have to be determined. This finding permits us to develop a fast approximate SCF semiempirical procedure offering a reliable tool for studying conformational problems in rather large (bio)molecules. As a first example, a model of the active site of α‐chymotrypsin was examined. According to our calculations, a hydrogen bond between Ser‐195 and His‐57 should exist.
Calculation of diamagnetic susceptibilities from the Thomas–Fermi–Amaldi theory for ions
Authors: Donnamaria Maria C. , Castro Eduardo A. , Fernández Francisco M.
Published: December 2004

The importance of the Fermi–Amaldi correction for the Thomas–Fermi theory for ions is analyzed. An analytical trial electron density with a proper limiting behavior has been chosen and the Thomas–Fermi–Amaldi energy expression is minimized in a variational way for several closed‐shell ions. The obtained optimum electron densities have been used for calculating the diamagnetic susceptibilities, and a comparison with other theoretical results and available experimental data is performed.
Symmetry operators of generalized wreath products and their applications to chemical physics
Authors: Balasubramanian K.
Published: December 2004

Symmetry operators of generalized wreath product groups are formulated. Several applications of these operators to nonrigid molecular problems in chemical physics are outlined.
SCF and MC–SCF Study of CO2 with bond angle variation
Authors: Combs Leon L. , Lunell Sten
Published: December 2004

Multiconfiguration (MC) SCF calculations are reported for CO2 for bond angles between 60° and 180°. The ground state configuration is found to be …︁5a4b∣b∣a for small bending angles and …︁6a3b∣b∣a for large bending angles, the change in ground state character occurring at a bond angle of about 100°. The force constant for bending obtained from the MC–SCF function is about 8.0% lower than the corresponding SCF value, and in considerably better agreement with experiment.
Molecular geometry of benzosemiquinone radicals: Radicals from resorcinol and its derivatives
Authors: Shinagawa Yasuko , Koyama Seiji , Shinagawa Yoshiya
Published: December 2004

The observed proton hyperfine coupling constants of radicals from resorcinol and 2‐carboxylic, 5‐carboxylic, and 5‐methyl resorcinols in acidic and alkaline solution were reproduced by means of the INDO (intermediate neglect of differential overlap) with molecular geometry adjusting method. The bond lengths of CO were longer in acidic solution than in alkaline solution and the total energies were lower in acidic solution than in alkaline solution. The assignments of the coupling constants of the radicals from resorcinols were |A2| > |A5| in alkaline oxidation and |A2| < |A5| in acidic oxidation.
Theoretical determination of the X2Σ+ and A2Π potentials of CsO using relativistic effective core potentials
Authors: Laskowski Bernard C. , Langhoff Stephen R. , Siegbahn Per E. M.
Published: December 2004

Theoretical potential energy curves are computed for the X 2Σ+ and A 2Π states of CsO using a relativistic effective core potential and a large valence Gaussian basis set. Seventeen electrons are correlated by a CI(SD) calculation from each HF reference. We find the X 2Σ+ state lower by 497 and 726 cm−1 at the HF and CI(SD) levels. Our calculated ωe of 312 cm−1 for the X 2Σ+ state agrees well with experimental values deduced from studies in matrices.
Potential energy surface determinations for nonrigid molecules: Application to acetone
Authors: Smeyers Yves G. , Bellido M. Nieves
Published: December 2004

In the present work, the problem of the determination of the potential energy surface for nonrigid molecules is examined in the case of the double rotation of the methyl groups in acetone. From the symmetry adapted functional form for the potential, the minimum number of configurations to be calculated is deduced in order to have a reliable surface. With this consideration in mind, the potential energy surface of acetone is determined in some Hartree–Fock semiempirical (CNDO/2) and ab initio procedures with different standard basis sets. In addition, ab initio calculations are performed using different sets of floating Gaussian functions in order to introduce some polarization effects in the wave function. Finally, the influence of the electronic correlation effects in the barrier height, and the role of the possible relaxation of the structure during the rotation is discussed.
Avoided crossing of molecular excited states and photochemistry: Butadiene and unprotonated Schiff base
Authors: Bonačić‐Koutecký V. , Persico M.
Published: December 2004

Consequences of the twisting motion around the CC bond of butadiene and around CC, CN, and CC bonds of the small unprotonated Schiff base (allylideneimine) on low‐lying singlet and triplet states have been investigated employing large scale CI treatments. Characterization of the important features of the electronic wave functions in terms of VB‐like ionic and covalent contributions in different twist intervals has been carried out. Importance of the zwitterionic singlet states with large charge separation in two different parts of molecule attached to the relaxed bond versus low‐lying covalent excited state has been discussed. Photochemical implications of different minima on the energy hypersurfaces of the excited states with different features of electronic wave functions have been proposed.
Water chain intervention in hydrolytic and tautomeric reactions
Authors: Bertrán J. , Lledós A. , Revetllat J. A.
Published: December 2004

Water chain intervention in the hydrolysis of methyl fluoride and in some tautomeric 1,3 proton transfer reactions has been studied. The results show that in solution the process are neither unimolecular nor bimolecular as in the gas phase, but are multimolecular, where the geometric parameters of the solvent intervene in the reaction coordinate.
Electrostatic and relaxation effects in ionization of molecular dimers and intermolecular complexes
Authors: Peel J. Barrie
Published: December 2004

The shifts in ionization energies which occur when a molecule is incorporated as an asymmetric dimer or in an intermolecular complex are analyzed theoretically. MOSCF calculations with 4–31G basis sets were performed on closed‐ and open‐shell states of (HF)2, H2O·HF, and their valence–hole ions, as well as on the heterodimers incorporating the higher homologues CH3F, CH3OH, and (CH3)2O. The analysis concerns the influence of electrostatic, polarization, and charge transfer effects associated with complexation on the initial molecular state of each monomer system, as well as monomer–dimer differences in the electronic relaxation mechanism considered as a final state effect in the ionization process. The calculated ionization energy shifts which agree well with the experimental data available for (CH3)2O·HF, show that the shifts are dominated by electrostatic effects, but some effects arising from differences in molecular size and electric polarizability of the monomers can be discerned.
Time‐dependent Schrödinger equations: Symmetry breaking, separation of variables, and nonlinear effects
Authors: Truax D. Rodney
Published: December 2004

Nonlinear equations are important for the description of dissipative processes and soliton‐related phenomena. One of the principal aims of the theory of symmetry breaking in quantum mechanics is to provide a systematic method for introducing interactions which reduce the symmetry of a system. Such a method is applied here to compute the general form of the symmetry‐breaking interaction F(x,t, Ψ, Ψ*) for the time‐dependent Schrödinger equation in one spatial dimension

For F = 0, it has been shown that the Lie algebra of space–time invariances of this equation is S1 = s1 (2,IR)□w1, the Schrödinger algebra. Following the method of Boyer, Sharp, and Winternitz, all conjugacy classes of subalgebras of S1 are given. For each subalgebra, the most general form of the interaction term F(x,t, Ψ, ψ*) is constructed. The potential F then reduces the symmetry from S1 to the considered subalgebra. Furthermore, the one‐dimensional subalgebras of S1 obtained above partition S1 into orbits of operators. To each orbit there corresponds a coordinate system in which the above equation separates variables. A partial resolution of the solutions of the above equation has been obtained by exploiting this relation. The algebraic approach to symmetry breaking yields a rich variety of interaction terms F, which appear to generalize the nonlinear Schrödinger–Langevin–Kostin equation for nonconservative systems and the so‐called nonlinear Schrödinger equation. A criterion in terms of the existence or nonexistence of Bäcklund transformations is conjectured in order to distinguish between dissipative and soliton equations.
Comments on the Bose condensation of phonons in the biological systems
Authors: Chatterjee R. , Tuszyński J. A. , Paul R.
Published: December 2004

Following the conjecture of Fröhlich that the Bose condensation of phonons is the dominant biological effect, Wu and Austin derived from the Fröhlich Hamiltonian an expression for the relaxation time which is inversely proportional to the temperature by using the technique of Green's function. In this paper, we have generalized the Wu and Austin expression by improving their approximations with the superconducting canonical transformation and obtained the relaxation time depending exponentially on the inverse temperature. Moreover, we have checked our expression by using a different method based on the “continued fraction expansion” and also employed this technique to derive the dielectric constant for this system.
Ab initio study of proton transfers including effects of electron correlation
Authors: Scheiner Steve , Szczȩlśniak Malgorzata M. , Bigham Larry D.
Published: December 2004

Proton transfers in a number of systems are investigated using ab initio molecular orbital methods. Calculations are carried out with several different basis sets ranging in size from 4–31G to 6–311G**. Electron correlation is included using Møller–Plesset (MP) perturbation theory to second and third orders. Enlargements of the basis set invariably lead to higher energy barriers to proton transfer, while substantial reductions result from inclusion of correlation effects. Application to (HOHOH)− of third‐order MP theory with a triple‐valence basis set augmented by polarization functions on oxygens and the central proton, denoted MP3/6–311G*(*), leads to excellent agreement with the results of Roos et al. whose calculations involved an extensive CI treatment with a large basis set. For equivalent hydrogen bond lengths, the transfer barrier in the cation (H2OHOH2)+ is nearly identical to that for the (HOHOH)− anion while the barrier in (H3NHNH3)+ is somewhat smaller. The reduction of the SCF barrier height resulting from inclusion of correlation is greater for (O2H3)− than for the above cations. The lowest energy structure of (O2H5)+ contains a symmetric hydrogen bond in which the proton is located midway between the two oxygens whereas asymmetric H bonds are found in the equilibrium geometries of (N2H7)+ and (S2H5)+. The difference in energy between the symmetric and asymmetric configurations of (O2H3)− is extremely small.
Energetics and electronic rearrangements of proton transfer in (H3NHOH2)+
Authors: Scheiner Steve
Published: December 2004

Proton transfer between N and O in the hydrogen‐bonded system (H3NHOH2)+ is studied by ab initio molecular orbital methods. Potential energy curves are calculated at the hartree–Fock level using the 4–31G basis set for hydrogen bond lengths R(NO) varying from the equilibrium value of 2.664 to 3.10 Å. Short hydrogen bonds are associated with asymmetric single‐well potentials in which the minimum corresponds to the NHO configuration. For longer R(NO) separations, the potential is of double‐well form, including both NHO and NHO as minima. It is found that the height of the energy barrier to proton transfer is sensitive to both stretches and bends of the hydrogen bond. Continuous changes in the electron density are monitored at various stages of proton transfer via density difference maps and Mulliken population analyses. The initial loss of density from the proton‐accepting molecule during the first half of the transfer is accelerated during the second half. A correlation is drawn between the energetics of transfer in a number of systems and the net charge lost by the proton‐acceptor group.
Integral evaluation algorithms and their implementation
Authors: Hegarty Dermot , Van Der Velde G.
Published: December 2004

Three different algorithms for the calculation of many center electron‐repulsion integrals are discussed, all of which are considered to be economic in terms of the number of arithmetic operations. The common features of the algorithms are as follows: Cartesian Gaussian functions are used, integrals are calculated by blocks (a block being defined as the set of integrals obtainable from four given exponents on four given centers), and functions may be adopted to R(3). Adaption to molecular point group symmetry is not considered. Tables are given showing the minimum number of operations for a selection of block types allowing one to identify the theoretically most economic, and the corresponding salient features. Comments concerning the computer implementations are also given both on sealar and vector processors. In particular, the Cyber 205 is considered, a vector processor on which we have implemented what we believe to be the most efficient algorithm.
Possible incorporation of the purine–purine mispairs in the DNA helix and the interpretation of the transversion‐type point mutations
Authors: Kothekar V. , Bolis G. , Rein Robert
Published: December 2004

The stereochemical and energetic compatibility of incorporation of the non‐Watson–Crick hydrogen bonded purine–purine base pairs of normal tautomers in the helical structure of B‐DNA is studied here. The hydrogen bonding positions of the possible “mispairs” of the bases GA, GG, and AA are optimized first in the base plane by translational and rotational movement along the hydrogen bonds and then introduced at an appropriate position in the DNA structure. The optimum backbone geometries which can accommodate the “mispairs” are obtained by force field computations. The stereochemical and energetic aspects of the various mispairs are discussed in light of their possible incorporation in DNA and as mutational intermediates for the “transversion”‐type point mutations.
Molecular electrotatic potential of a triple stranded helix: Poly(dT)·poly(dA)·poly(dT)
Authors: Corbin Sylvie , Lavery Richard , Pullman Bernard
Published: December 2004

The molecular electrostatic potential of the triple helix poly(dT)·tpoly(dA)·poly(dT) is calculated, and the results are examined in relation to those obtained for its component double and single helical parts. For the double helix presenting the standard Watson–Crick hydrogen bonds, the deepest potentials are formed on the side of the major groove, a situation similar to that observed in the A‐DNA duplex. For the double helix presenting Hoogsteen‐type hydrogen bonds the deepest potentials lie in the major groove, on the side of the pyrimidine strand. In the triple helix the deepest potentials are located in the major groove in a narrow zone over the thymine bases of the Watson–Crick pair.
Evaluation of GTO molecular integrals
Authors: Harris Frank E.
Published: December 2004

Methods for evaluating the function Fm(t) occurring in molecular integrals over Gaussian‐type orbitals are reviewed and extended. Formulas based on Bessel function and continued‐fraction expansions are analyzed. The recommended evaluation procedures, embodied in a portable computer program, involve Padé approximations for various argument intervals and use recursion in m. The program is economical in storage requirements and faster than those in current use.
Cluster Xα approach to magnetic interactions and phase transitions in solids
Authors: Gubanov V. A. , Liechtenstein A. I. , Postnikov A. V.
Published: December 2004

A magnetic transition state model is developed for the description of magnetic interactions and magnetic phase transitions in solids. The model is based on the one‐electron Xα molecular orbital calculations of clusters embedded in crystal lattice and allows quantitative investigations of magnetic interactions in d and f metals, their alloys, and compounds. The energies of local spin excitations and magnetic transition temperatures are calculated for a series of systems with the electronic states localized to a different extent. The effects of covalent bonding are introduced directly into magnetic parameters calculations and appear to be of crucial importance. Magnetic properties of some disordered alloys are considered basing on the results of Xα cluster calculations performed. In the low concentration limit, the local moment existence problem is being discussed. The dependence of magnetic properties upon concentration is considered. The results of calculations allow to give the reasonable interpretation of the experimental data available and show good possibilities of the cluster model in the description of magnetic effects in solids.
Use of VN−1 potentials in Green's function calculations
Authors: Winkler Peter
Published: December 2004

An analysis of the leading effects of a propagator approach to the calculation of resonance energies is presented. By comparison with ΔSCF results, a simple approximation formula has been developed which contains the main features of the VN−1 potential option and the diagonal Tamm–Dancoff approximation. This result is expected to be a useful guide for further refinements of the many‐body aspects of the theory.
Responses to light in individual growth and reproduction of two Acer species and the long‐term consequences
Authors: Uraguchi Aya , Kubo Takuya
Published: December 2004

Despite widespread interest in plant responses to light, few studies have addressed the lifetime consequences of the responses. We have addressed this issue by studying Acer mono and Acer amoenum trees in a cool temperate forest in northern Japan. By analyzing field data, it was detected that growth and flowering rates increased with light availability for each species. A stochastic individual‐based model consisting of growth, flowering, and survival processes was used to estimate lifetime reproductive outputs under three treatments of light conditions. These analyses indicated that A. mono had high variation in lifetime reproductive output under different light conditions, and that the variation was mainly caused by the growth response and not by the flowering response. In contrast, A. amoenum showed stable lifetime reproductive outputs across all light conditions. Our results demonstrated that responses detected by data analyses do not always lead to changes in lifetime reproductive output. This result highlights the importance of lifetime integration for the evaluation of the long‐term impact of performance responses. These results also revealed some of the ways in which individuals of the two Acer species may contribute to overall population regulation.
Young Citizens or Policy Objects? Children in the ‘Rights and Responsibilities’ Debate
Authors: SUCH ELIZABETH , WALKER ROBERT
Published: December 2004

Rights and responsibilities lie at the heart of New Labour's social policies. Children and young people present a challenge to the social contractual model of responsibility evident in policy spheres. Government is torn between the notion that children are dependent on parents for well-being, and the idea that individuals should take responsibility for their own actions. The article examines the problem of childhood in social policy through an examination of the conflicting messages emerging out of family policy and anti-social behaviour policies. Policy discourses are then critically evaluated with reference to a qualitative study of children's ideas about responsibility. The authors suggest that policies relating to children can learn from children's private experience of responsibility in the home, and from the complex and rich ways in which children understand the moral and relational components of responsibility.
Efficacy of broad‐spectrum sunscreens against the suppression of elicitation of delayed‐type hypersensitivity responses in humans depends on the level of ultraviolet A protection
Authors: Moyal D. D. , Fourtanier A. M.
Published: December 2004

Abstract: Sunscreens have been designed to protect against sunburn and their efficacy has, therefore, been labeled by the so‐called sun protection factor (SPF). Although this value is well determined using a standardized protocol and it affords a good evaluation of the protection against erythema it may be inadequate to provide a relevant measurement of efficacy against other biologic damages. This is particularly true when action spectra and threshold dose are different from those of erythema. In the case of ultraviolet (UV)‐induced immune suppression, the action spectrum is not known, so it cannot be asserted that SPF may accurately predict the level of protection against this endpoint. We addressed this issue by measuring in human volunteers the ability of two broad‐spectrum SPF 15 sunscreens with different ultraviolet A (UVA) protection levels, to prevent the alteration of the efferent phase of the local delayed‐type hypersensitivity (DTH) response to recall antigens (Multitest Pasteur/Mérieux, Lyon, France) after acute solar‐simulated UV exposure. We first determined the ultraviolet radiation (UVR) dose needed to induce a significant DTH inhibition in several groups of 15 volunteers. Two minimal erythemal doses (2 MED) were found to be the minimal immunosuppressive dose (MISD). As a result, the immune DTH response is reduced in average by 36%. The lower doses tested (0.5 and 1 MED) were ineffective. Sunscreen‐treated groups were exposed to either 1 or 2 MED × SPF doses. As expected, no alteration in DTH response was observed in the groups exposed to 1 MED × SPF whatever the sunscreen applied. In contrast, after exposure to 2 MED × SPF, the DTH response remained unaltered in the group pretreated with the sunscreen product with the higher protection in the UVA range but was significantly suppressed by 55.7% in the group pretreated with sunscreen with a much lower protection in the UVA range. These data suggest that SPF may not be sufficient to predict the ability of sunscreens to protect from UV‐induced immune suppression. Determining the level of UVA protection is particularly needed, as UVA seems to have a relatively low contribution to erythema but is highly involved in immunosuppression.
Matrix metalloproteinases in tumor progression: focus on basal and squamous cell skin cancer
Authors: Kerkelä E. , Saarialho‐Kere U.
Published: December 2004

Abstract: Many normal biological processes, such as reproduction, fetal development and wound healing, are critically dependent on controlled degradation of extracellular matrix (ECM) macromolecules. However, excessive degradation of matrix components occurs in pathologic tissue destruction, e.g. in atherosclerosis, rheumatoid arthritis, and cancer. Matrix metalloproteinases (MMPs) are degradative enzymes that play an important role in all aspects of tumor progression by enhancing tumor‐induced angiogenesis and destroying local tissue architecture and basement membranes to allow tumor invasion and metastasis. Efficient breakdown of the ECM surrounding invasive cancer islands involves interplay between tumor cells, stromal cells, and inflammatory cells, all of which express a distinct set of MMPs. Besides the classical role of MMPs in degradation of ECM, MMPs may also indirectly influence the tumor microenvironment through the release of growth factors, cryptic sites or angiogenic factors, or through the generation of matrix fragments that inhibit tumor cell proliferation, migration and angiogenesis. This makes the contribution of MMPs to tumorigenesis much more complex than initially thought. Currently, a number of clinical studies have focused on testing MMP inhibitors as potential antineoplastic agents. In this review we discuss the present role of MMPs in the development and progression of cancer, focusing on non‐melanoma skin cancers basal (BCC) and squamous (SCC) cell carcinoma, and the possible influence of MMPs in their differences.
Ultraviolet‐B irradiation decreases IFN‐γ and increases IL‐4 expression in psoriatic lesional skin in situ and in cultured dermal T cells derived from these lesions
Authors: Piskin Gamze , Koomen Cornelis W. , Picavet Daisy , Bos Jan D. , Teunissen Marcel B. M.
Published: December 2004

Abstract: Type 1 cytokine producing T cells play an important role in the pathogenesis of psoriasis. Ultraviolet‐B (UVB) irradiation is effective in the treatment of this disease. In normal skin, UVB causes a change in dermal microenvironment, leading to a decrease of IFN‐γ expressing type 1 T cells and a concurrent increase of IL‐4 expressing type 2 T cells. The aim of this study was to show whether UVB irradiation causes a like‐wise shift of type 1 and type 2 responses in psoriatic skin. For this purpose, biopsies were obtained from the lesional skin of psoriatic patients before, 2 days and 14 days after a single exposure to 4 MED UVB. Sections from these biopsies were immunostained (CD3, IFN‐γ and IL‐4) or RNA was extracted and analyzed for the expressions of IFN‐γ and IL‐4 by PCR. In addition, primary cultures of T cells from dermal cell suspensions were stained intracellularly for IFN‐γ and IL‐4 expression and CD4+ and CD8+ T subsets were analyzed by flow cytometry. IFN‐γ was abundantly expressed in situ before irradiation and decreased in all patients after UVB irradiation, whereas IL‐4 expression was variably expressed before irradiation and increased in different degrees after irradiation. Cytokine mRNA expressions determined by PCR showed a clear decrease of IFN‐γ and increase of IL‐4 following UVB irradiation. Both CD4+ and CD8+ dermal T cells were found to produce less IFN‐γ and more IL‐4 following UVB irradiation as determined by flow cytometry. Decrease in IFN‐γ expression and increase in IL‐4 expression of dermal T cells in psoriatic lesions after UVB irradiation may lead to decrease in local immunoreactivity. These changes could be part of the therapeutic effects of UVB on psoriasis.