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1.
The radial electron-pair intracule (relative motion) H(u) and extracule (center-of-mass motion) D(R) densities in position space were known to reveal four types of maxima which are related to the four inner electron shells,
K, L, M, and N, of atoms. The corresponding radial electron-pair intracule Hˉ(v) and extracule Dˉ(P) densities in momentum space are studied for the 102 atoms from He (atomic number Z=2) to Lr (Z=103). The densities Hˉ(v) and Dˉ(P) are found to have either one maximum or two maxima, and the numbers of maxima in Hˉ(v) and Dˉ(P) are the same for 98 atoms. For these atoms, the locations υ
max and P
max and the heights Hˉ
max
and Dˉ
max
of the corresponding maxima satisfy the approximate relations υ
max ≅ 2P
max and Hˉ
max
≅Dˉ
max
/2. On the basis of their Z-dependence, the maxima in Hˉ(v) and Dˉ(P) of the 102 atoms are classified into five types. Shell-pair decompositions of the radial densities show that these maxima
reflect five outer electron shells of atoms.
Received: 24 January 2001 / Accepted: 12 March 2001 / Published online: 13 June 2001 相似文献
2.
Friedrich Grein 《Theoretical chemistry accounts》2003,109(5):274-277
Using 6-31G and 6-311G basis sets to which diffuse and polarization functions were added in a stepwise fashion (a total of
16 basis sets), Hartree–Fock (HF), MP2 and B3LYP geometry optimizations were performed on biphenyl. With the MP2 method, diffuse
functions raise the dihedral angle φ, for example, from 46.3° for 6-31G to 54.1° for 6-311++G, while polarization functions
lower it, for example, from 54.1° for 6-311++G to 42.1° for 6-311++G(2d,2p). For a single set of polarization functions, φ(MP2)
lies close to or above φ(HF) (44–47°), but for a double set it is below φ(HF) and is close to B3LYP values (38–42°) which
show little basis set dependence. The most reliable value for φ, 42.1° [MP2/6-311++G(2d,2p)], is expected to increase slightly
by adding more diffuse functions. The corresponding best calculated energy barrier at 0° (coplanar conformation) is 2.83 kcal/mol,
much higher than the experimental estimate (1.4 ± 0.5 kcal/mol). The barrier at 90° is 1.82 kcal/mol, in line with the experimental
estimate (1.6 ± 0.5 kcal/mol) and with previous theoretical results.
Received: 9 September 2002 / Accepted: 15 November 2002 /
Published online: 1 April 2003
Correspondence to: Friedrich Grein e-mail: fritz@unb.ca
Acknowledgement. The author would like to thank NSERC (Canada) for financial support. 相似文献
3.
For the 53 neutral atoms from He to Xe in their ground states, the average distances < u>
n
l
,
n
′
l
′ in position space and < v>
n
l
,
n
′
l
′ in momentum space between an electron in a subshell nl and another electron in a subshell n
′
l
′ are studied, where n and l are the principal and azimuthal quantum numbers of an atomic subshell, respectively. Analysis of 1700 subshell pairs shows
that the electron-pair distances < u>
n
l
,
n
′
l
′ in position space have an empirical but very accurate linear correlation with a one-electron quantity U
n
l
,
n
′
l
′≡L
r
+S
r
2/(3L
r
), where L
r
and S
r
are the larger and smaller of subshell radii < r>
n
l
and < r>
n
′
l
′, respectively. The correlation coefficients are never smaller than 0.999 for the 66 different combinations of two subshells
appearing in the 53 atoms. The same is also true in momentum space, and the electron-pair momentum distances < >
n
l
,
n
′
l
′ have an accurate linear correlation with a one-electron momentum quantity V
n
l
,
n
′
l
′≡L
p
+S
p
2/(3L
p
), where L
p
and S
p
are the larger and smaller of average subshell momenta < p>
n
l
and < p>
n
′
l
′, respectively. Trends in the proportionality constants between < u>
n
l
,
n
′
l
′ and U
n
l
,
n
′
l
′ and between < >
n
l
,
n
′
l
′ and V
n
l
,
n
′
l
′ are discussed based on a hydrogenic model for the subshell radial functions.
Received: 8 April 1998 / Accepted: 6 July 1998 / Published online: 18 September 1998 相似文献
4.
Toshikatsu Koga 《Theoretical chemistry accounts》2002,107(4):246-249
On the basis of multiconfiguration Hartree–Fock calculations, correlated electron-pair intracule (relative motion) and extracule
(center-of-mass motion) properties are reported for the Li atom in momentum space. The present results are more accurate and
consistent than those in the literature.
Received: 10 September 2001 / Accepted: 11 December 2001 / Published online: 22 March 2002 相似文献
5.
M.M. Hurley J.B. Wright G.H. Lushington W.E. White 《Theoretical chemistry accounts》2003,109(3):160-168
The accurate modeling of biological processes presents major computational difficulties owing to the inherent complexity
of the macromolecular systems of interest. Simulations of biochemical reactivity tend to require highly computationally intensive
quantum mechanical methods, but localized chemical effects tend to depend significantly on properties of the extended biological
environment – a regime far more readily examined with lower-level classical empirical models. Mixed quantum/classical techniques
are gaining in popularity as a means of bridging these competing requirements. Here we present results comparing two quantum
mechanics/molecular mechanics implementations (the SIMOMM technique of Gordon et al. as implemented in GAMESS, and the ONIOM
technique of Morokuma et al. found in Gaussian 98) as performed on the enzyme acetylcholinesterase and model nerve agents.
This work represents part of the initial phase of a DoD HPCMP Challenge project in which we are attempting to reliably characterize
the biochemical processes responsible for nerve agent activity and inhibition, thereby allowing predictions on compounds unrelated
to those already studied.
Received: 10 October 2001 / Accepted: 13 November 2002 / Published online: 1 April 2003
Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 222nd National Meeting of the American
Chemical Society, 2001
Correspondence to: M. M. Hurley e-mail: hurley@arl.army.mil 相似文献
6.
Steven M. Bachrach Joseph M. Hayes Trang Dao Justin L. Mynar 《Theoretical chemistry accounts》2002,107(5):266-271
Density functional calculations indicate that nucleophilic substitution in the thiolate–disulfide and thiolate–trisulfide
exchange reactions proceeds by an addition–elimination pathway. Solution calculations were performed using B3LYP/6-31+G* and
the polarized continuum method. These solution-phase calculations indicate that for the reactions where the sulfur under attack
bears a hydrogen atom, the substitution proceeds via an addition–elimination mechanism; however, when a methyl group is attached
to the sulfur under attack, the SN2 mechanism is predicted.
Received: 12 October 2001 / Accepted: 28 November 2001 / Published online: 8 April 2002 相似文献
7.
Davor Margetić Ronlad N. Warrener Mirjana Eckert-Maksić Ivana Antol Zoran Glasovac 《Theoretical chemistry accounts》2003,109(4):182-189
DFT calculations of 7′–oxasesquinorbornenes and 7,7′-dioxasesquinorbornenes using the B3LYP/6–31G* method are reported.
All the investigated structures (syn- and anti- derivatives) showed significant non-planarity of the central double bond, with the exception of those anti-derivatives possessing symmetrical structures. The influence of the replacement of the methylene groups at position 7- of
the norbornene fragment with oxygen and the introduction of second and third (peripheral) double bonds and benzene rings on
the molecular and electronic structures of these molecules have also been investigated.
Received: 11 November 2002 / Accepted: 6 June 2002 /
Published online: 29 April 2003 相似文献
8.
P. Thanikaivelan J. Padmanabhan V. Subramanian T. Ramasami 《Theoretical chemistry accounts》2002,107(6):326-335
The use of Fukui functions for the site selectivity of the formaldehyde molecule for nucleophilic, electrophilic and radical
attacks has been made with special emphasis to the dependence of Fukui values on the basis sets as well as population schemes
in the framework of B3LYP theory. Out of the five population schemes selected viz., Mulliken population analysis, natural
population analysis, CHELP, CHELPG and atoms in molecules (AIM), it is found that the CHELPG and AIM schemes predict precise
reactive site with less dependency on the basis sets. Charges derived from Hirshfeld partitioning, calculated using the BLYP/dnd
method (implemented in the DMOL3 package), provide non-negative Fukui values for all the molecular systems considered in this study. Supporting results have
been obtained for acetaldehyde and acetone molecules at the 6-31+G** basis set level. These results support the fact that
high Fukui values correspond to soft–soft interaction sites. On the other hand, the correlation of the low Fukui value to
the hard–hard interaction site merits further investigation.
Received: 10 November 2001 / Accepted: 6 March 2002 / Published online: 13 June 2002 相似文献
9.
José A. Rodriguez 《Theoretical chemistry accounts》2002,107(3):117-129
The surface chemistry of oxides is relevant for many technological applications: catalysis, photoelectrolysis, electronic-device
fabrication, prevention of corrosion, sensor development, etc. This article reviews recent theoretical works that deal with
the surface chemistry of oxides. The account begins with a discussion of results for the adsorption of CO and NO on oxides,
systems which have been extensively studied in the literature and constitute an ideal benchmark for testing the quality of
different levels of theory. Then, systematic studies concerned with the behavior of adsorbied alkali metals and sulfur-containing
molecules are presented. Finally, a correlation between the electronic and chemical properties of mixed-metal oxides is analyzed
and basic principles for designing chemically active oxides are introduced. Advances in theoretical methods and computer capabilities
have made possible a fundamental understanding of many phenomena associated with the chemistry of molecules on oxide surfaces.
Still many problems in this area remain as a challenge, and the approximate nature of most theoretical methods makes necessary
a close coupling between theory and experiment. Following this multidisciplinary approach, the importance of band-orbital
interactions for the reactivity of oxide surfaces has become clear. Simple models based on band-orbital mixing can explain
trends found for the interaction of many adsorbates with oxide surfaces. These simple models provide a conceptual framework
for modifying or controlling the chemical activity of pure oxides and for engineering mixed-metal oxides. In this respect,
theoretical calculations can be very useful for predicting the best ways for enhancing the reactivity of oxide systems and
reducing the waste of time, energy and materials characteristic of an empirical design.
Received: 21 June 2001 / Accepted: 8 October 2001 / Published online: 1 February 2002 相似文献
10.
Michael P. Barnett 《Theoretical chemistry accounts》2002,107(4):241-245
In the course of checking our work on the symbolic calculation of molecular integrals over Slater orbitals, we obtained some
results in substantial disagreement with two recent articles that describe numerical schemes. We believe that these schemes
suffer from digital erosion, possibly because recurrence formulas were used outside their regions of stability. Our results
were obtained using the ζ-function method, which expands the orbital on one atom onto the other, and integrates in polar coordinates.
They were checked using elliptic coordinates. Both sets of calculations were performed symbolically. We summarize these calculations
and discuss the impact of symbolic calculation on the accuracy of molecular computations.
Received: 31 August 2001 / Accepted: 29 October 2001 / Published online: 8 April 2002 相似文献
11.
Jon Applequist 《Theoretical chemistry accounts》2002,107(2):103-115
The nature of the Maxwell–Cartesian spherical harmonics S
(n)
K
and their relation to tesseral harmonics Y
nm
is examined with the help of “tricorn arrays” that display the components of a totally symmetric Cartesian tensor of any
rank in a systematic way. The arrays show the symmetries of the Maxwell–Cartesian harmonic tensors with respect to permutation
of axes, the traceless properties of the tensors, the linearly independent subsets, the nonorthogonal subsets, and the subsets
whose linear combinations produce the tesseral harmonics. The two families of harmonics are related by their connection with
the gradients of 1/r, and explicit formulas for the transformation coefficients are derived. The rotational transformation of S
(n)
K
functions is described by a relatively simple Cartesian tensor method. The utility of the Maxwell–Cartesian harmonics in
the theory of multipole potentials, where these functions originated in the work of Maxwell, is illustrated with some newer
applications which employ a detracer exchange theorem and make use of the partial linear independence of the functions. The
properties of atomic orbitals whose angular part is described by Maxwell–Cartesian harmonics are explored, including their
angular momenta, adherence to an Uns?ld-type spherical symmetry relation, and potential for eliminating an angular momentum
“contamination” problem in Cartesian Gaussian basis sets.
Received: 9 July 2001 / Accepted: 7 September 2001 / Published online: 19 December 2001 相似文献
12.
Transport cross sections and collision integrals are tabulated for a wide range of energies and temperatures for the interactions
B–B and Al–Al. For aluminum, a semiclassical approximation was used to determine the scattering phase shifts from which the
transport cross sections were calculated. For boron, the smaller reduced mass and the deep potential wells required the phase
shifts at lower energies to be determined from a numerical solution of the time-independent Schroedinger equation; the semiclassical
approximation was used at higher energies where the two methods agree. The variations of the collision integrals for viscosity
and diffusion are presented graphically as a function of temperature. The results are applied to estimate the transport properties
of gallium.
Received: 9 July 1999 / Accepted: 18 August 1999 / Published online: 2 November 1999 相似文献
13.
The relationship between band structure and the topology of the orbital interactions between neighboring chemical units comprising
several model one-dimensional polymers with helical (screw-axis) symmetry is analyzed. A perturbative model of orbital interactions
based on a tight binding implementation of the extended Hückel method is developed. The model accounts for both the band topologies
and the seemingly anomalous band extrema within the Brillouin zone constructed using the chemical repeat unit of the polymer.
Received: 5 November 2001 / Accepted: 14 January 2002 / Published online: 3 May 2002 相似文献
14.
J. F. Ogilvie S.-L. Cheah Y.-P. Lee S. P. A. Sauer 《Theoretical chemistry accounts》2002,108(2):85-97
From quantum-chemical calculations of rotational g factor and new experimental measurements of strengths of lines in infrared spectra of vibration–rotational bands v′–0 in absorption, with 1≤v′≤4, of 12C16O, and from analysis of 16,947 frequencies and wave numbers assigned to pure rotational and vibration–rotational transitions
within electronic ground state X
1Σ+, including new measurements of band 4–0 of 12C16O, we evaluate radial functions for potential energy and electric dipolar moment, the latter both in polynomial form and as
a rational function that has qualitatively correct behaviour under limiting conditions.
Received: 8 November 2001 / Accepted: 5 February 2002 / Published online: 14 August 2002 相似文献
15.
Binding energies of helium, neon and atomic hydrogen encapsulated inside a C20 cage were calculated using an ab initio method at the B3LYP/6-31+G⋆ level of theory. The standard equilibrium constants for
the reactions of noble-gas atoms going into the C20 molecular cage have also been studied. The transition states for the reactions of C20 with hydrogen and helium were further obtained with an ab initio method at the B3LYP/6-31+G⋆ level and the rate constants
were estimated by using conventional transition-state theory. It was found that the hydrogen and helium atoms are extremely
difficult to put into the C20 cage. Once inside the cage, a helium atom can hardly get out, while a hydrogen atom can easily escape from the cage. The
results are expected to enrich fullerene science and be helpful for fullerene applications such as storage.
Received: 2 November 2002 / Accepted: 19 December 2002 /
Published online: 30 April 2003
Correspondence to: R. Q. Zhang, e-mail: aprqz@cityu.edu.hk
Acknowledgements. The work described in this paper was jointly supported by a grant from the City University of Hong Kong (project no. 7001222)
and a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (project no. 9040633/CityU,
1011/01P]. 相似文献
16.
The self-interaction error (SIE) of commonly used density functional theory (DFT) exchange functionals mimics long-range
(nondynamic) pair correlation effects in an unspecified way. Slater exchange suffers from a larger SIE and, therefore, covers
more nondynamic correlation effects than Becke exchange, which is the reason why exchange–correlation (XC) functionals based
on Slater exchange lead to stabler restricted DFT solutions than those based on Becke exchange. However, the stability of
an XC functional does not guarantee higher accuracy. On the contrary, if system-specific nondynamic correlation effects have
to be introduced via the form of the wave function, these will be suppressed by nondynamic correlation effects already covered
by the exchange functional. Hybrid functionals suffer less from the SIE and, therefore, cover a smaller number of nondynamic
electron correlation effects. Accordingly, they are better suited when nondynamic electron correlation has to be introduced
by the form of the wave function. It is shown that, for example, broken-symmetry unrestricted DFT calculations are more accurate
when carried out with B3LYP than BLYP contrary to claims made in the literature.
Received: 8 November 2001 / Accepted: 30 January 2002 / Published online: 8 April 2002 相似文献
17.
18.
W. A. de Jong R. J. Harrison J. A. Nichols D. A. Dixon 《Theoretical chemistry accounts》2001,107(1):22-26
A complete set of fully-relativistic benchmark results for the bond lengths and vibrational frequencies of uranyl at various
levels of correlation treatment are presented. It is shown that the relativistic and correlation effects are of the same magnitude
and should be treated on an equal footing. Results of uranyl calculations using various relativistic effective core potentials
(RECP) are presented. Appropriate choices for RECPs for use in density functional theory (DFT) calculations in the local density
approximation (LDA) and with the gradient-corrected B3LYP exchange-correlation functional are discussed. The conclusion is
reached that small-core RECPs need to be used and that the best results as compared to the benchmark values are obtained by
using a DFT functional that includes some fraction of Hartree-Fock Exchange.
Received: 18 May 2001 / Accepted: 25 July 2001 / Published online: 30 October 2001 相似文献
19.
P. Reinhardt 《Theoretical chemistry accounts》2000,104(6):426-438
The techniques of matrix dressing for configuration-interaction (CI)-type or coupled-electron-pair-approximation (CEPA)-type
correlation treatments are reviewed with respect to the application to periodic systems. All methods ranging from canonical
second-order M?ller–Plesset perturbation theory over CI of single and double excitation, CEPA-0 or the averaged-coupled-pair-functional
to self-consistent size-consistent CI can be formulated completely equivalently as an eigenvalue problem or as a solution
to a system of linear equations. The size consistency of each method is obtained in a natural way, and invariance under orbital
rotations is clearly assessible. A remark on the size consistency of the Davidson correction is presented. Additionally, the
direct generation of localized Hartree–Fock orbitals as basic ingredients for the correlation calculations are addressed,
as well as selected results on ring molecules, polymers, and 3D cubic beryllium as a model crystal.
Received: 28 August 1999 / Accepted: 5 March 2000 / Published online: 21 June 2000 相似文献
20.
The effect of truncating singles + doubles configuration interaction (CISD) and singles + doubles + triples + quadruples
(CISDTQ) spaces on the energies of the systems Ne, H2O, CO and C2 is investigated through the use of a previously described, general, selected CI program. CI expansions generated by Hartree–Fock
orbitals as well as by natural orbitals are examined and the latter typically exhibit faster convergence as regards the energy.
For the CISD wavefunctions of Ne, H2O, CO and C2, chemical accuracy is reached by using, respectively, 34, 47, 53 and 55% of the full sets. For the triples + quadruples parts
of the wavefunctions on the other hand, chemical accuracy is already reached by using only 1, 4, 6 and 9% of the respective
full sets.
Received: 14 August 2001 / Accepted: 6 December 2001 / Published online: 8 April 2002 相似文献