bluuebunny/crossref_metadata_2025_split huggingface dataset:
The tautomers of uracil: A local correlation treatment
Authors: Boughton James W. , Pulay Peter 
Published: December 2004

AbstractThe relative energies of all six uracil tautomers have been determined at the MP4(SDQ)/6‐31G** level, using both conventional correlation theory and the Local Correlation method. Geometries were optimized at the SCF/6‐31G* level with offset forces. Comparison of our energies with energies from structures optimized at the SCF level supports the conclusion that offset forces are an advantageous alternative to correlated geometry optimization. The Local Correlation method compares very well with conventional Møller–Plesset theory, recovering at least 98.4% of the conventional correlated energy in all cases. More importantly, the relative energies also show good agreement with the conventional results, even for these delocalized systems. CPU timings show a substantial computational savings for the Local Correlation method over the conventional method. The results of the local method using Boys localization are compared with those using Pipek–Mezey localization. The dioxo tautomer (1) is predicted to be the most stable. The (1)–(3) and (1)–(4) energy differences are found to be within the bounds estimated from experimental work. © 1993 John Wiley & Sons, Inc.
Gaussian expansions from STOs by the distance between subspaces
Authors: De La Vega J. M. Garcia , Miguel B. 
Published: December 2004

AbstractExpansions of STO orbitals with GTOs for the first‐row atoms have been obtained by the method of the distance between subspaces. The expansion coefficients and exponential parameters were simultaneously varied when the distance between subspaces, which are generated from STO and GTO functions, is minimized. The ζ; exponents (or scale factors) for the atomic orbitals that are optimized for these atoms are also shown to be almost independent of the number of Gaussian functions. Comparisons carried out with Stewart's least‐squares method produce equivalent results when exponents for 2s and 2p functions are different. Some examples and applications for several atomic properties of the first‐row atoms are included: energies and expectation values of ri and pi for the several expansions. These new minimal basis sets were tested for diatomic and polyatomic molecules containing these atoms. © 1993 John Wiley & Sons, Inc.
Coupled cluster Green's function method: Working equations and applications
Authors: Nooijen Marcel , Snijders Jaap G. 
Published: December 2004

AbstractDetailed working equations are derived for the ionization part of the single‐particle Green's function within the coupled cluster Green's function (CCGF) framework. The CCGF method is applied to the calculation of vertical ionization potentials (IPs) of a number of small molecules, notably, HF, N2, CO, F2, CS, C2H4, H2O, and H2CO. The results for the outer‐valence IPs, with an average error of 0.12 eV, compare favorably to third‐order equation‐of‐motion calculations within the same basis set (average error 0.28 eV) and outer‐valence GF (OVGF) values taken from the literature (average error 0.17 eV). Ground‐state properties that derive from the CCGF are compared to expectation values obtained in the related normal coupled cluster methods (NCCM) approximation from a formal point of view. Correlation energies obtained in CCGF are compared to CCSD results for the above series of molecules and, in addition, the so‐called true correlation energy density as obtained from the CCGF is compared to the result from an accurate MR–CI calculation for a highly correlated system: the HF molecule at large internuclear separation. © 1993 John Wiley & Sons, Inc.
Electronic structures of high‐Tc superconductors LnBa2Cu3O7 (Ln  Pr, Nd, Gd, Dy)
Authors: Li Ming 
Published: December 2004

AbstractIn the present paper, the electronic energy‐band structures of the LnBa2Cu3O7 (Ln = Pr, Nd, Gd, and Dy) were investigated employing the EHMO approach based on the tight‐binding method. The results show that the substitution of Nd, Gd, and Dy for Y in YBa2Cu3O7 complicates the shape of the Fermi surface and results in an increase in the number of energy bands crossing the Fermi level, Ef. Compared with those of YBa2Cu3O7, the electronic densities of states at Ef, N(Ef), for NdBa2Cu3O7, GdBa2Cu3O7, and DyBa2Cu3O7 increase greatly, whereas those of PrBa2Cu3O7 are very small. The results given by the present calculations explain why the substitution of Nd, Gd, and Dy for Y in YBa2Cu3O7 can still maintain the high transition temperature Tc, while PrBa2Cu3O7 is a semiconductor rather than a superconductor. © 1993 John Wiley & Sons, Inc.
Molecular surface electrostatic potentials and local ionization energies of Group V–VII hydrides and their anions: Relationships for aqueous and gas‐phase acidities
Authors: Brinck Tore , Murray Jane S. , Politzer Peter 
Published: December 2004

AbstractWe have computed ab initio HF/6‐31+G* electrostatic potentials and average local ionization energies on the molecular surfaces of the Group V–VII hydrides and corresponding anions of the first three rows of the periodic table. The surfaces were defined to be specified contours (0.002 or 0.001 au) of the molecular electronic density. The most negative potentials, VS,min, and lowest ionization energies ĪS,min, were located and determined. Their magnitudes separately satisfy limited correlations with gas‐phase protonation enthalpies and aqueous pKa values. Our results indicate that VS,min, and ĪS,min are complementary, the former reflecting electrostatic factors and the latter being related to charge transfer/polarization. More general relationships for protonation enthalpies are obtained when both VS,min and ĪS,min are explicitly included. Solution‐phase and gas‐phase acidities are shown to correlate very well if electrostatic effects are explicitly taken into account. © 1993 John Wiley & Sons, Inc.
Early stages of LiX, BeH2X, and BH3X pyrolysis (X stands for NH3 or OH2): A theoretical study of weak dative complex stability
Authors: Sana Michel , Leroy Georges 
Published: December 2004

AbstractIn this work, we study theoretically the thermal decomposition of weak dative complexes (namely, the complexes between BH3, BeH2, or LiH and ammonia or water). The most accurate calculations have been carried out at the MP4sdtq/6‐311++G(3df,2p) level on MP2full/6‐31G** fully optimized geometries. The transition structures for hydrogen evolution are described. The rate constants were obtained using conventional transition‐state theory. Stability conditions for the complexes were considered. Water complexes are less stable than are the corresponding ammonia derivatives. Lithium complexes seem to be very unstable. It seems that beryllium compounds could be synthesized. Borane derivatives are known experimentally. We find, as observed, that the first hydrogen evolution occurs only above room temperature. Iminoborane seems not to be easily accessible under pyrolysis conditions. Other reactions require less activation energy. Finally, the early stages of the ammonia–borane pyrolysis and paths to open‐chain polymers as well as to cyclic structures are described. © 1993 John Wiley & Sons, Inc.
On the Car–Parrinello computational scheme: Rigorous treatment
Authors: Kryachko Eugene S. 
Published: December 2004

AbstractGiven a manifold of parameters associated with a trial many‐electron wave function to evolve in a fictitious time, the Lagrangian of the corresponding classical system of the parameters' degrees of freedom is constructed explicitly for the case of the closed‐shell Hartree–Fock approximation. The relevant equations of motion of a non‐Newtonian type are derived. The formulae for the masses of the parameters' degrees of freedom are obtained in the limit of small velocities. The Newtonian dynamics described by the Car–Parrinello Lagrangian is discussed. © 1993 John Wiley & Sons, Inc.
Band structures of al‐doped superconductors YBa2Cu3–xALxO7 + δ
Authors: Ming Li 
Published: December 2004

AbstractBased on the EHMO approach, an approximate treatment of electronic energy‐band structures is suggested. By employing this treatment, computations of the band structures for the Al‐doped superconductors YBa2Cu3–xAlxO7 + δ were carried out. It is shown by analysis of the band structures and the density of states that the 2D Cu–O planes in the YBa–CuO superconducting system play a dominant role in superconductivity, whereas the 1D CuO ribbons have indirectly an influence on superconductivity through the connection of the O(4) atoms to two CuO planes. © 1994 John Wiley & Sons, Inc.
On multireference superdirect configuration interaction in third order
Authors: Duch Włodzisław , Meller Jarosław 
Published: December 2004

AbstractThe superdirect configuration interaction (Sup‐CI) method has the usual versatility and stability of the CI methods with computational efficiency typical to that of the many‐body methods, such as the many‐body perturbation theory (MBPT). The Hamilton operator is projected into a space of a few trial vectors, such as Krylov, Nesbet, or Møller–Plesset correction vectors. In this space, Hamiltonian matrix elements may be directly computed in the many‐body fashion, as weighted sums of integral products over orbital indices. The variation‐perturbation method based on the first‐order wave function is equivalent to the Sup‐CI method with a single correction vector of the Møller–Plesset type. Different points of view on the superdirect CI method are discussed and a version in which third‐order contributions are computed for a relatively small (10–100) space of reference and correction vectors is tested. Selection of the best “effective first‐order spaces” and size‐extensivity corrections in Sup‐CI are briefly discussed. Møoller–Plesset, Epstein–Nesbet, and other correction vectors are included in the model calculations on the symmetric stretch of bonds in water, acetylene, and the NH2 molecule. Errors are almost independent of molecular geometry and the method appears to be superior than the multireference second‐order perturbation methods. © 1994 John Wiley & Sons, Inc.
Second quantization and coefficients of fractional parentage
Authors: Bernotas Andrius , Kaniauskas Julius 
Published: December 2004

AbstractThe coefficients of fractional parentage (CFP), treated by tradition as antisymmetrizing multipliers, do not exist as such in the second‐quantization representation, because, therein, by definition, there is nothing to antisymmetrize. This by no way means that the above‐mentioned representation is less relevant in theoretical atomic spectroscopy than is any other one. On the contrary, all the well‐known mathematical apparatus is still successfully applied, alongside with numerous new useful features. Moreover, the analysis presented here yields some results not so obvious from the point of view of the coordinate representation, namely, the consequent application of the second‐quantization representation led us to an expansion of many‐shell wave functions employing analogs of many‐shell CFP, which appeared to be considerably simpler than the traditional CFP expansion. Also, a generalization of Redmond's formula for the case of many‐shell CFP and a straightforward method of deriving summation rules for products of CFP are clear in the second‐quantization representation and are sketched here. © 1994 John Wiley & Sons, Inc.
Ab initio study of molecular g‐tensors
Authors: Lushington G. H. , Bündgen P. , Grein F. 
Published: December 2004

AbstractThe molecular g‐tensors for the molecules NO2, CO, C3H5, H2CO+, and NF are calculated at the unrestricted Hartree–Fock (UHF) level using the Rayleigh–Schrödinger perturbation approach. All one‐electron terms have been evaluated, including the relativistic mass correction, the one‐electron spin–Zeeman gauge correction, and a second‐order term involving the spin–orbit coupling and the orbital–Zeeman interaction. The relative importance of the first‐order terms is found to be quite substantial. For first‐row molecules, their total contribution is often of the same order of magnitude as of the second‐order contribution, in some instances even larger. A study on the basis‐set dependence of these g‐tensors has been conducted. At this level, the most important basis‐set criterion is shown to be a satisfactory description of the valence regions. Finally, the gauge dependence of these g‐tensor calculations has been systematically studied. This dependence seems to be substantially reduced for basis sets which include polarization functions. © 1995 John Wiley & Sons, Inc.
Discrete variable representation method applied to the determination of J = 0 vibrational bound states of NO2
Authors: Vilanove H. , Jacon M. 
Published: December 2004

AbstractThe discrete variable representation method (DVR) is applied to the calculation of the J = 0 vibrational energy levels of the ground electronic state of nitrogen dioxide, a molecule which shows a large amplitude bending vibration. The Hamiltonian is expressed in Johnson hyperspherical coordinates and developed on a DVR basis set for each coordinate. A successive diagonalization–truncation method is applied which gives accurate values for the energy levels up to ≃ 7000 cm−1. © 1995 John Wiley & Sons, Inc.
Cytomegalovirus and Epstein–Barr virus DNA transcription in endodontic symptomatic lesions
Authors: Sabeti M. , Valles Y. , Nowzari H. , Simon J. H. , Kermani‐Arab V. , Slots J. 
Published: December 2004

Objectives:  Productive Herpesviridae infections are implicated in the etio‐pathogenesis of aggressive periodontitis. However, virtually nothing is known about a possible role of herpesviruses in pulpal and periapical pathosis. This study employed a cDNA analysis to determine transcription of human cytomegalovirus (HCMV), Epstein–Barr virus (EBV) and herpes simplex virus (HSV) in 14 recalcitrant periapical lesions and in 2 periapical healthy control sites.Methods:  Periapical samples were collected in conjunction with periapical surgery and kept frozen until virologic examination. RNA was isolated from periapical tissue by using a guanidinium isothiocyanate‐acid phenol procedure (TRIZOL LS Reagent, GIBCO BRL, Rockville, MD). cDNAs were amplified by means of oligonucleotides targeting highly conserved regions of the test viruses and the RT‐PCR‐100 amplification kit (Sigma–Aldrich, St Louis, MO). Standardization of PCR primer sensitivity and validation was carried out according to established methods. Amplification products were identified by agarose gel electrophoresis.Results:  HCMV transcript was detected in 12 of 13 symptomatic and in 1 asymptomatic periapical lesion. EBV transcript was demonstrated in 8 of the 13 symptomatic lesions but not in the asymptomatic periapical lesion. HCMV and EBV dual transcription occurred at higher frequency in periapical lesions showing radiographic bone destruction of 5 mm × 7 mm or larger than in smaller size lesions (P = 0.03; Chi‐squared test). No HCMV or EBV transcription was identified in the 2 healthy control sites. HSV transcript was not detected in any study site.Conclusion:  The present data suggest that HCMV or EBV infections participate in the pathogenesis of periapical symptomatic lesions. Herpesviruses may produce periapical pathosis as a direct result of viral infection and replication, or as a consequence of virally induced impairment of the host defense and subsequent increased virulence of resident bacterial pathogens.
Calcification of the interclinoid and petroclinoid ligaments of sella turcica: a radiographic study of the prevalence
Authors: Cederberg R.A. , Benson B.W. , Nunn M. , English J.D. 
Published: December 2004

Structured AbstractAuthors – Cederberg RA, Benson BW, Nunn M, English JDObjectives – The purpose of this study was to evaluate the prevalence of calcifications of the sella turcica, in particular, calcification of the interclinoid and petroclinoid ligaments (PCL).Design – Radiographic analysis of preoperative cephalometric film images.Setting and Sample Population – Lateral cephlometric radiographs of 255 subjects presenting for orthodontic evaluation were reviewed. The number of subjects selected for this study was determined by power analysis.Experimental Variable – Two calibrated raters reviewed cephalometric projections and scored the films using a standardized rating scale.Outcome Measure – The rating scale classified interclinoid ligaments (ICL) into one of four categories depending on the degree of calcification and PCLs as either, no calcification, partial or complete calcification.Results – Of all subjects, calcification of the ICL ranged from 39% rated as more than half calcified to 8% completely calcified. Petroclinoid analysis revealed 67% with no calcification, 23% with partial calcification and 9% completely calcified. Spearman's correlations were computed between age and the degree of calcification and between the degree of calcification for these two ligaments with a significant association between age and degree of calcification in the PCL, r = 0.185 (p = 0.003) and a significant association between the degree of calcification in the petroclinoid and ICLs, r = 0.186 (p = 0.003). In addition, chi‐squared tests demonstrated statistically significant associations between the presence of calcification in the PCL to the distribution of age (p = 0.041) and between the presence of calcification in the ICL to the distribution of age (p = 0.045).Conclusion – As calcification of these ligaments has suggestive associations with disease entities, their recognition as a variant of normal anatomy should be evaluated when assessing cephalometric radiographs.
Identification of Risk for High Hospital Use: Cost Comparisons of Four Strategies and Performance Across Subgroups
Authors: Reuben David B. , Keeler Emmett , Seeman Teresa E. , Sewall Ase , Hirsch Susan H. , Guralnik Jack M. 
Published: December 2004

OBJECTIVES: To determine the relative costs of four risk‐identification strategies and compare their performance in predicting hospital use by different subgroups of older persons based on age, sex, and prior hospital use.DESIGN: Prospective validation study and cost‐comparison analysis.SETTING: Community‐based.PARTICIPANTS: Five thousand one hundred thirty‐eight participants of the sixth wave of three sites of the Established Populations for Epidemiologic Studies of the Elderly.MEASUREMENTS: Four strategies (prior hospitalization data only, a 10‐item self‐report screen alone, self‐report combined with two laboratory tests, and sequential self‐report plus as‐needed use of laboratory tests when the self‐report screen is inconclusive) and 3‐year Medicare Part A hospital cost data.RESULTS: Assuming that interventions based on screening would yield a total benefit of $1,000 per true‐positive case and a cost of $400 for each false‐positive case, the sequential strategy was slightly less expensive than the self‐report only strategy; both were considerably less expensive than the combined or hospitalization‐only strategies. Accuracy as measured by the area under the receiver operating characteristic curve for the sequential strategy was comparable for all subgroups (between 0.62 and 0.70) but was least accurate for those who had high prior use and for those aged 85 and older.CONCLUSION: A sequential screening strategy that administers laboratory tests selectively is slightly less expensive than one that uses only self‐report items. This strategy is also accurate in both sexes, in those with various degrees of prior use, and in the oldest old.
Handgrip Strength and Cause‐Specific and Total Mortality in Older Disabled Women: Exploring the Mechanism
Authors: Rantanen Taina , Volpato Stefano , Luigi Ferrucci MD , Eino Heikkinen MD , Fried Linda P. , Guralnik Jack M. 
Published: December 2004

OBJECTIVES: To examine the association between muscle strength and total and cause‐specific mortality and the plausible contributing factors to this association, such as presence of diseases commonly underlying mortality, inflammation, nutritional deficiency, physical inactivity, smoking, and depression.DESIGN: Prospective population‐based cohort study with mortality surveillance over 5 years.SETTING: Elderly women residing in the eastern half of Baltimore, Maryland, and part of Baltimore County.PARTICIPANTS: Nine hundred nineteen moderately to severely disabled women aged 65 to 101 who participated in handgrip strength testing at baseline as part of the Women's Health and Aging Study.MEASUREMENTS: Cardiovascular disease (CVD), cancer, respiratory disease, other measures (not CVD, respiratory, or cancer), total mortality, handgrip strength, and interleukin‐6.RESULTS: Over the 5‐year follow‐up, 336 deaths occurred: 149 due to CVD, 59 due to cancer, 38 due to respiratory disease, and 90 due to other diseases. The unadjusted relative risk (RR) of CVD mortality was 3.21 (95% confidence interval (CI) = 2.00–5.14) in the lowest and 1.88 (95% CI = 1.11–3.21) in the middle compared with the highest tertile of handgrip strength. The unadjusted RR of respiratory mortality was 2.38 (95% CI = 1.09–5.20) and other mortality 2.59 (95% CI = 1.59–4.20) in the lowest versus the highest grip‐strength tertile. Cancer mortality was not associated with grip strength. After adjusting for age, race, body height, and weight, the RR of CVD mortality decreased to 2.17 (95% CI = 1.26–3.73) in the lowest and 1.56 (95% CI = 0.89–2.71) in the middle, with the highest grip‐strength tertile as the reference. Further adjustments for multiple diseases, physical inactivity, smoking, interleukin‐6, C‐reactive protein, serum albumin, unintentional weight loss, and depressive symptoms did not materially change the risk estimates. Similar results were observed for all‐cause mortality.CONCLUSION: In older disabled women, handgrip strength was a powerful predictor of cause‐specific and total mortality. Presence of chronic diseases commonly underlying death or the mechanisms behind decline in muscle strength in chronic disease, such as inflammation, poor nutritional status, disuse, and depression, all of which are independent predictors of mortality, did not explain the association. Handgrip strength, an indicator of overall muscle strength, may predict mortality through mechanisms other than those leading from disease to muscle impairment. Grip strength tests may help identify patients at increased risk of deterioration of health.