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1.
Marten J. Ten Hoor 《International journal of quantum chemistry》1988,33(5):467-475
For the Hartree–Fock ground state of atomic two-electron systems, the variational function of Wilson and Silverstone, ?(r) = (a + kr)?1 exp(-kr) / (4π)1/2, can be optimized in two complementary ways. For small values of the atomic number Z, all intergrals have been calculated numerically and optimization can be performed accurately. However, as Z increases, loss of significant figures is increasingly detrimental to the optimization process. For sufficiently large values of Z, the integrals may be replaced by asymptotic expansions in terms of (2a)?. As a result of optimization, the parameters and expectation values can be given as expansions in terms of (32Z)?1/2. Both methods yield good results for Z ≈ 25, so that the whole range of Z can be treated accurately. The results have been compared with those derived from other analytical two-parameter functions. It is found that ?(r) is indeed the outstanding two-parameter function, at least for small and intermediate values of Z. 相似文献
2.
Two phosphonodehydrotripeptides: Boc0–Gly1–Δ(Z)Phe2–α‐Abu3PO3Me2 and Boc0–Gly1–Δ(Z)Phe2–α‐Nva3PO3Et2
Anna Brzuszkiewicz Maciej Makowski Marek Lisowski Elbieta Lis Marta Otrba Tadeusz Lis 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(3):277-281
The present paper reports the crystal structures of two short phosphonotripeptides (one in two crystal forms) containing one ΔPhe (dehydrophenylalanine) residue, namely dimethyl (3‐{[tert‐butoxycarbonylglycyl‐α,β‐(Z)‐dehydrophenylalanyl]amino}propyl)phosphonate, Boc0–Gly1–Δ(Z)Phe2–α‐Abu3PO3Me2, C21H32N3O7P, (I), and diethyl (4‐{[tert‐butoxycarbonylglycyl‐α,β‐(Z)‐dehydrophenylalanyl]amino}butyl)phosphonate, Boc0–Gly1–Δ(Z)Phe2–α‐Nva3PO3Et2, as the propan‐2‐ol monosolvate 0.122‐hydrate, C24H38N3O7P·C3H8O·0.122H2O, (II), and the ethanol monosolvate 0.076‐hydrate, C24H38N3O7P·C2H6O·0.076H2O, (III). The crystals of (II) and (III) are isomorphous but differ in the type of solvent. The phosphono group is linked directly to the last Cα atom in the main chain for all three peptides. All the amino acids are trans linked in the main chains. The crystal structures exhibit no intramolecular hydrogen bonds and are stabilized by intermolecular hydrogen bonds only. 相似文献
3.
Quadrupole and octupole polarizabilities for the ground states of lithiumlike systems from Z=3 to 20
The quadrupole and octupole polarizabilities for the ground states of lithiumlike systems from Z=3 to 20 are calculated with the full-core plus correlation method. For the neutral lithium atom, the typical patterns of convergence of the quadrupole and octupole polarizabilities are analyzed. The calculated quadrupole and octupole polarizabilities of the ground state for lithium atom are compared with the previous theoretical results obtained by other methods; our predictions agree with the most accurate reports in the literature very well. For lithiumlike ions, our prediction may provide valuable reference data for other accurate theoretical calculations in future. 相似文献
4.
Karinne Miqueu Jean-Marc Sotiropoulos Patrick Baylre Sylvie Joantguy Genevive Pfister-Guillouzo Henri Ranaivonjatovo Jean Escudi Mereyim Bouslikhane 《Journal of Molecular Structure》2004,690(1-3):53-61
The electronic properties of a diarsaallene ArAs=C=AsAr and a phosphaarsaallene ArP=C=AsAr (Ar: 2,4,6-tri-tert-butylphenyl) have been investigated by using UV photoelectron spectroscopy and by density functional calculations on model compounds [(CH3)2C6H3Pn=C=AsC6H3(CH3)2, Pn: As, P]. Moreover, a comparison of the geometrical and electronic structures of the parent heteroallenes with those of the arsaethene H2C=AsH and phosphaethene H2C=PH has also been undertaken in order to determine the magnitude of the interaction between the π bond and the pnictogen lone pair nPn. 相似文献
5.
Combined CI –HY method techniques have been employed in obtaining a 57-term CI –HY wave function with an energy of ?14.66632 a.u. A method due to Brown has been adopted for obtaining this wave function and various shorter expansions. A 44-term expansion with an energy of ?14.66606 a.u. is analyzed in terms of various pair effects, and qualitative arguments are presented for understanding these effects. 相似文献
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7.
Summary The paper deals with two topics related to the problem which reference state is better for many-body perturbation theory: restricted Hartree-Fock (RHF) or unrestricted Hartree-Fock (UHF)? The first topic concerns the potential surfaces. Several examples are presented to show shortcomings of the two approaches and a simple way is presented which seems to give a useful potential curve in the whole range of interatomic distances by a composition of RHF and UHF potential curves. The second topic concerns the many-body perturbation theory for open-shell systems in the RHF formalism. The method is critically examined and compared with the ordinary many-body perturbation theory using UHF as the reference. This examination of many-body techniques provides also some insight into the problems inherent of the SCF theory: spin contamination from higher multiplets, localization of orbitals, and self-consistency effects. 相似文献
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9.
In order to investigate the magnetic properties of the solid solution CePt1–xPdxAl the individual compounds were synthesized from the elements using an arc furnace. From x = 0–0.8 the solid solution crystallizes in the orthorhombic TiNiSi‐type structure (Pnma, no. 62; a = 721–722, b = 448–453 and c = 778–779 pm) and for x = 0.9 both the TiNiSi‐ as well as the hexagonal ZrNiAl‐type structures were observed. The solid solution exhibits an interesting magnetic behavior as for small values of x ferromagnetic ordering can be found. At higher palladium content this changes towards an antiferromagnetic ordering. Furthermore the solid solution exhibits a spin‐reorientation (meta‐magnetic step) for x = 0.2–0.7. 相似文献
10.
A novel algorithm is introduced for coding all Slater determinants in the covalent space with conserved SZ, the z component of total spin S for a classical valence bond (VB) model. It effectively minimizes the search time and the storing space in the central memory of the computer. In cooperation with symmetry reductions based on molecular point group and spin inversion, the VB calculations have been extended to benzenoid hydrocarbons of up to 28 π‐electrons that have 4×107 configurations. The low‐lying states of benzenoids with 24, 26, and 28 π‐electrons have been obtained for 62 species. To rationalize the aromaticity of benzenoids in a VB scheme, the resonance energy per hexagon (REPH) is defined. A linear correlation between the REPH and the energy gap of the ground (singlet) state and the first excited (triplet) state for 89 benzenoids is established. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 856–869, 2000 相似文献
11.
Frolov AM 《The Journal of chemical physics》2006,124(22):224323
The total energies and various bound state properties are determined to very high accuracy for the ground 1 (1)S(L=0) states in some light two-electron ions, including the Li(+), Be(2+), B(3+), and C(4+) ions. The corrections due to the finite nuclear masses and lowest order QED corrections ( approximately alpha(3)) are considered/computed for each of these ions. In particular, the specific mass shift is determined for each of the Li(+), Be(2+), B(3+), and C(4+) ions. We also discuss the field shift related to the extended nuclear charge distribution. 相似文献
12.
Jean-Claude Leclerc 《International journal of quantum chemistry》1976,10(5):781-789
Introduction of noninteger powers of r (or the elliptical coordinate ξ) in the definition of the 1s AO is shown to give better approximate wave-functions for the ground states of H2 and He than other functions of comparable complexity. This trend is examined for various definitions of hybrid Slater–Gaussian orbitals using a limited CI . The best optimized single-term expansion energy is only 0.000160 a.u. above the “SCF limit” for H2 at R = 1.4 a.u. and 0.000382 a.u. for He at R = 1.3 a.u. 相似文献
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14.
α and α are derived for use in spin polarized Hartree–Fock–Slater programs. They are assumed to depend only on the number of up and down spin electrons in the atom. The calculated eigenvalues show a slight improvement only for carbon, nitrogen, and oxygen. 相似文献
15.
The solid solution CeRu1–xPdxAl was synthesized for x = 0.1–0.9 from the elements by arc‐melting and subsequent annealing and characterized by powder X‐ray diffraction. All members crystallize in the orthorhombic LaNiAl type structure, space group Pnma. The lattice parameters range from a = 718–722, b = 412–426, and c = 1588–1620 pm, but no linear change of the lattice parameters was found. Magnetic measurements reveal intermediate cerium valences, which change to more trivalent cerium with increasing Pd content. The susceptibility data was interpreted by either the Inter‐Configuration Fluctuation (ICF) model or the Curie‐Weiss law. 相似文献
16.
Elizabeth Florez Patricio Fuentealba 《International journal of quantum chemistry》2009,109(5):1080-1093
A theoretical study of the electronic structure of the first members of the alkali metal atomic clusters series Lin to Csn (n = 2–8) has been done. The geometries of some isomers of the neutral, positive, and negative charged clusters have been determined. Some important properties have also been calculated: atomic binding energies, vertical and adiabatic ionization potentials, vertical and adiabatic electron affinities, static dipole polarizabilities, and energy gaps. Whenever possible they have been compared with experimental values yielding a reasonable agreement which supports some new values as reliable predictions. The data have been discussed in light of the periodic table of elements trends. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
17.
Carlos M. Sanabria Sandra L. Gmez Alirio Palma Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(11):o540-o546
(2S*,4R*)‐2‐exo‐(1‐Naphthyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C20H17NO, (I), crystallizes with Z′ = 2 in the space group P21; the two independent molecules have the same absolute configuration, although this configuration is indeterminate. The molecules of each type are linked by a combination of C—H...O and C—H...π(arene) hydrogen bonds to form two independent sheets, each containing only one type of molecule. (2SR,4RS)‐7‐Methyl‐2‐exo‐(1‐naphthyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C21H19NO, (II), crystallizes as a true racemate in the space group P21/c, and a combination of C—H...N, C—H...O and C—H...π(arene) hydrogen bonds links the molecules into sheets, each containing equal numbers of the two enantiomorphs. (2S*,4R*)‐2‐exo‐(1‐Naphthyl)‐7‐trifluoromethyl‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C21H16F3NO2, (III), crystallizes as a single enantiomorph, as for (I), but now with Z′ = 1 in the space group P212121; again, the absolute configuration is indeterminate. A single C—H...π(arene) hydrogen bond links the molecules of (III) into simple chains. (2S,4R)‐8‐Chloro‐9‐methyl‐2‐exo‐(1‐naphthyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C21H18ClNO, (IV), crystallizes as a single enantiomorph of well defined configuration, in the space group P212121, where two independent C—H...π(arene) hydrogen bonds link the molecules into a single three‐dimensional framework structure. 相似文献
18.
Cristin Crdenas-Lailhacar Michael C. Zerner 《International journal of quantum chemistry》1995,55(6):429-439
A procedure for finding transition states ( TS ) that does not require the evaluation of the second derivatives during the search is proposed. The procedure is based on connecting a series of points representing products P i and reactants R i and taking conservative steps along the difference vector from P i toward R i and from R i toward P i until the two points coalesce. Although the points P o and R o represent the product and reactant specifically, other P i and R i are determined by minimization in hyperplanes perpendicular to P i ?1 and R i?1. We apply this technique to six well-known potential functions and compare these results with those obtained from other well-known procedures. © 1995 John Wiley & Sons, Inc. 相似文献
19.
Giovanni L. Cascarano George Ferguson Carmelo Giacovazzo Christopher Glidewell Anthony L. Spek 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(7):774-777
A fully ordered structure is reported for the polymorph of triphenylsilanol–4,4′‐bipyridyl (4/1), 4C18H16OSi·C10H8N2, having Z′ = 4. The asymmetric unit contains four similar but distinct five‐molecule aggregates, in which the central bipyridyl unit is linked to two molecules of triphenylsilanol via O—H...N hydrogen bonds, with a further pair of triphenylsilanol molecules linked to the first pair via O—H...O hydrogen bonds. An extensive series of C—H...π(arene) hydrogen bonds links these aggregates into complex sheets. This structure is compared with a previously reported structure [Bowes, Ferguson, Lough & Glidewell (2003). Acta Cryst. B 59 , 277–286], which was based on an erroneous disordered structural model arising from a false direct‐methods solution with reference to a strong pseudo‐inversion centre. 相似文献
20.
Giuseppe Werber Francesco Buccheri Nicol Vivona Manlio Gentile 《Journal of heterocyclic chemistry》1978,15(8):1393-1398
The factors influencing the reactivity of α-thienylglyoxal monosemicarbazones when treated with cyclizing reagents (bromine/sodium acetate and hydrobromic acid in acetic acid) were investigated. Depending on the experimental conditions, on the position of the substituent on the semicarbazide residue, and on the cyclizing agent, the substrates 1a-e give the semicarbazone bromides 2a-b, 5 , the 1,3,4-oxadiazoles 3a-c , the 1,2,4-triazine 11 and the 2,3,4,5-tetrahydro-1,2,4-triazine-3-ones 6, 8 and 9 . Compound 6 by thermolysis undergoes ring contraction in the Δ2-1,3,4-oxadiazoline 12 , while treatment with base involves the conversion of 6 into 1,2,4-triazol-5-one 13 . Ir, nmr and mass spectra support the reported structures. 相似文献