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1.
Michael Bühl 《Theoretical chemistry accounts》2002,107(6):336-342
Gradient-corrected (GGA) and hybrid variants of density functional theory are used to compute geometries and 55Mn chemical shifts of MnO4
−, Mn(CO)6
+, Mn2(CO)10, Mn(CO)5
X [X=H, Cl, C(O)Me], Mn(CO)5
−, Mn(NO)3(CO), and Mn(C5H5)L
x
[L
x
=(CO)3, C6H6, C7H8]. For this set of compounds, substituent effects on δ(55Mn) are significantly underestimated with the pure GGA functional BPW91 and are well described with hybrid functionals such
as mPW1PW91 and, in particular, B3LYP. The computed data provide evidence for solvent and counterion effects on δ(55Mn) of MnO4
− and Mn(CO)6
+, respectively. The latter, in the presence of Cl−, may be described as highly fluxional Mn(CO)5C(O)Cl. Electric field gradients computed with the B3LYP functional can be used for a qualitative rationalization of observed
trends in 55Mn NMR line widths. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located
at http://dx.doi.org/10.1007/s002140020338x
Received: 17 January 2002 / Accepted: 13 March 2002 / Published online: 3 June 2002 相似文献
2.
The ground state and several low-lying excited states of the Mg2 dimer have been studied by means of a combination of the complete-active-space multiconfiguration self-consistent-field (CASSCF)/CAS
multireference second-order perturbation theory (CASPT2) method and coupled-cluster with single and double excitations and
perturbative contribution of connected triple excitations [CCSD(T)] scheme. Reasonably good agreement with experiment has
been obtained for the CCSD(T) ground-state potential curve but the dissociation energy of the only experimentally known A1Σ
u
+ excited state of Mg2 is somewhat overestimated at the CASSCF/CASPT2 level. The spectroscopic constants D
e, R
e and ωe deduced from the calculated potential curves for other states are also reported. In addition, some spin–orbit matrix elements
between the excited singlet and triplet states of Mg2 have been evaluated as a function of internuclear separation.
Received: 10 May 2001 / Accepted: 15 August 2001 / Published online: 30 October 2001 相似文献
3.
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
4.
Maurizio Guerra 《Theoretical chemistry accounts》2000,104(6):455-460
Calculations with the density functional theory (DFT) method using the most popular functional, Becke's three parameter hybrid
with the Lee, Yang and Parr correlation functional, predict the π-delocalized configuration of the vinylacyl radical, CH2=CH—C(•)=O, to be more stable than the σ-localized configuration in contrast with ab initio unrestricted quadratic configuration
interaction with single and double excitations calculations as previously found for the isoelectronic vinyl radical, Y-C(•)=CH2, bearing π-type α substituents. Experimental evidence on the electronic configuration adopted by vinyl radicals is contrasting.
In the present case comparison with experiment indicates firmly that the currently available density functionals overestimate
the stability of π-delocalized versus σ-localized configurations in radicals since they favor the π configuration for the
γ-methylvinylacyl radical, CH3—CH=CH—C(•)=O, in contrast with unequivocal electron spin resonance data. This failure is mainly due to an incorrect estimate
of dynamic correlation energy with DFT functionals.
Received: 13 January 2000 / Accepted: 16 March 2000 / Published online: 21 June 2000 相似文献
5.
Ab initio calculations have been performed to study the molecular structures and vibrational levels of the four low-lying
ionic states (1, 22Π, and 1, 22Σ+) of carbonyl sulfide. The global regions of the potential-energy surfaces have been obtained by multireference single and
double excitation configuration interaction calculations. Vibrational calculations using explicit vibrational Hamiltonians
have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of the four ionic
states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states
are also presented and are compared with the photoelectron spectrum.
Received: 20 January 2001 / Accepted: 22 August 2001 / Published online: 30 October 2001 相似文献
6.
Victor Polo Jürgen Gräfenstein Elfi Kraka Dieter Cremer 《Theoretical chemistry accounts》2003,109(1):22-35
Exchange functionals used in density functional theory (DFT) are generally considered to simulate long-range electron correlation
effects. It is shown that these effects can be traced back to the self-interaction error (SIE) of approximate exchange functionals.
An analysis of the SIE with the help of the exchange hole reveals that both short-range (dynamic) and long-range (nondynamic)
electron correlation effects are simulated by DFT exchange where the local density approximation (LDA) accounts for stronger
effects than the generalized gradient expansion (GGA). This is a result of the fact that the GGA exchange hole describes the
exact exchange hole close to the reference electron more accurately than the LDA hole does. The LDA hole is more diffuse,
thus leading to an underestimation of exchange and stronger SIE effects, where the magnitude of the SIE energy is primarily
due to the contribution of the core orbitals. The GGA exchange hole is more compact, which leads to an exaggeration of exchange
in the bond and the nonbonding region and negative SIE contributions. Partitioning of the SIE into intra-/interelectronic
and individual orbital contributions makes it possible to test the performance of a given exchange functional in different
regions of the molecule. It is shown that Hartree–Fock exchange always covers some long-range effects via interelectronic
exchange while self-interaction-corrected DFT is lacking these effects.
Received: 25 May 2002 / Accepted: 7 October 2002 / Published online: 21 January 2003
Correspondence to: E. Kraka e-mail: kraka@theoc.gn.se
Acknowledgements. This work was supported financially by the Swedish Natural Science Research Council (NFR). Calculations were done on the
supercomputers of Nationellt Superdatorcentrum (NSC), Link?ping, Sweden. The authors thank the NSC for a generous allotment
of computer time. 相似文献
7.
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
8.
We assess the performance of the Van Voorhis–Scuseria exchange–correlation functional (VSXC), a kinetic-energy-density-dependent
exchange–correlation functional recently developed in our group, for calculating vertical excitation energies using time-dependent
density functional theory in a benchmark set of molecules. Overall, VSXC performs very well, with accuracy similar to that of hybrid functionals such as the hybrid Perdew–Burke–Ernzerhof functional
and Becke's three parameter hybrid method with the Lee, Yang, and Parr correlation functional, which contain a portion of
Hartree–Fock exchange.
Received: 29 December 1999 / Accepted: 5 June 2000 / Published online: 11 September 2000 相似文献
9.
Ab initio molecular orbital theory and density functional theory have been used to study nine isomers of N7 ionic clusters with low spin at the HF/6-31G*, MP2/6-31G*, B3LYP/6-31G*, and B3LYP/6-311(+)G* levels of theory. All stationary
points are examined with harmonic vibrational frequency analyses. Four N7
+ isomers and five N7
− isomers are determined to be local minima or very close to the minima on their potential-energy hypersurfaces, respectively.
For N7
+ and N7
−, the energetically low lying isomers are open-chain structures (C
2
v
and C
2
v
or C2). The results are very similar to those of other known odd-number nitrogen ions, such as N5
+, N9
+, and N9
−, for which the open-chain structures are also the global minima. This research suggests that the N7 ionic clusters are likely to be stable and to be potential high-energy-density materials if they could be synthesized.
Received: 16 July 2001 / Accepted: 8 October 2001 / Published online: 21 January 2002 相似文献
10.
Jordi Poater Miquel Solà Miquel Duran Xavier Fradera 《Theoretical chemistry accounts》2002,107(6):362-371
Localization, λ(A), and delocalization indices, δ(A,B), as defined in the atoms in molecules theory, are a convenient tool for the analysis of molecular electronic structure from
an electron-pair perspective. These indices can be calculated at any level of theory, provided that first- and second-order
electron densities are available. In particular, calculations at the Hartree–Fock (HF) and configuration interaction (CI)
levels have been previously reported for many molecules. However, λ(A) and δ(A,B) cannot be calculated exactly in the framework of Kohn–Sham (KS) density functional theory (DFT), where the electron-pair
density is not defined. As a practical workaround, one can derive a HF-like electron-pair density from the KS orbitals and
calculate approximate localization and delocalization indices at the DFT level. Recently, several calculations using this
approach have been reported. Here we present HF, CI and approximate DFT calculations of λ(A) and δ(A,B) values for a number of molecules. Furthermore, we also perform approximate CI calculations using the HF formalism to obtain
the electron-pair density. In general, the approximate DFT and CI results are closer to the HF results than to the CI ones.
Indeed, the approximate calculations take into account Coulomb electron correlation effects on the first-order electron density
but not on the electron-pair density. In summary, approximate DFT and CI localization and delocalization indices are easy
to calculate and can be useful in the analysis of molecular electronic structure; however, one should take into account that
this approximation increases systematically the delocalization between covalently bonded atoms, with respect to the exact
CI results.
Received: 13 February 2002 / Accepted: 24 April 2002 / Published online: 18 June 2002 相似文献
11.
Rita Prosmiti Alexei A. Buchachenko Pablo Villarreal Gerardo Delgado-Barrio 《Theoretical chemistry accounts》2001,106(6):426-433
Ab initio molecular electronic structure calculations are performed for H5
+ at the QCISD(T) level of theory, using a correlation-consistent quadruple-zeta basis set. Structures, vibrational frequencies
and thermochemical properties are evaluated for ten stationary points of the H5
+ hypersurface and are compared with previous calculations. The features of the H3
+…H2 interaction at intermediate and large intermolecular distances are also investigated. Furthermore, an analytical functional
form for the potential-energy surface of H5
+ is derived using a first-order diatomics-in-molecule perturbation theory approach. Its topology is found to be qualitatively
correct for the short-range interaction region.
Received: 15 March 2001 / Accepted: 5 July 2001 / Published online: 11 October 2001 相似文献
12.
A series of correlation-consistent basis sets are developed for Fe. Our best computed 5F–5D separation in the Fe atom is in excellent agreement with experiment. Our best estimate for the FeCO D
0 value is in good agreement with experiment. The 5Σ−–3Σ− separation in FeCO has an error of 3.6 kcal/mol; while the origin of this error is not clear, it is probably not due to the
basis set.
Received: 5 March 2001 / Accepted: 2 May 2001 / Published online: 9 August 2001 相似文献
13.
Low-spin/high-spin energy splittings for Fe(II) transition-metal complexes – particularly in weak ligand fields – cannot
be well described by density functional methods. Different density functionals yield results which differ by up to 1 eV in
transition-metal complexes with sulfur-rich first coordination spheres. We attribute this failure to the fact that the high-spin
state is systematically favoured in Hartree–Fock-type theories, because Fermi correlation is included in the exact exchange,
while Coulomb correlation is not. We thus expect that the admixture of exact exchange to a given density functional will heavily
influence the energy splitting between states of different multiplicity. We demonstrate that the energy splitting depends
linearly on the coefficient of exact exchange admixture. This remarkable result is found for all the Fe(II)–S complexes studied.
From this observation we conclude in connection with experimental results that Becke's 20% admixture should be reduced to
about 15% if meaningful energetics are sought for transition-metal compounds. We rationalize that this reduction by 5% will
not affect the quality of the hybrid functional since we arrive at a slightly modified functional, which lies between the
pure density functional and the hybrid density functional, which both give good results for “standard” systems.
Received: 13 July 2001 / Accepted: 31 August 2001 / Published online: 16 November 2001 相似文献
14.
The electron affinities of Ti, V, Cr, Fe, Co, Ni, and Cu are computed using the density function theory and CCSD(T) approaches.
Overall the CCSD(T) approach yields the best results. For this property, the B3LYP, BLYP, and BP86 functionals perform better
than the BPW91, PBEPBE, and PBE1PBE ones. The accuracy of all the methods is higher if the number of 3delectrons is the same in the neutral atom and the anion. This is especially true for the density functional theory methods.
Received: 23 January 2002 / Accepted: 1 April 2002 / Published online: 24 June 2002 相似文献
15.
The most stable structures of V
x
O
y
+/V
x
O
y
(x=1, 2, y=1–5) clusters and their interaction with O2 are determined by density functional calculations, the B3LYP functional with the 6-31G* basis set. The nature of the bonding
of these clusters and the interaction with O2 have been studied by topological analysis in the framework of both the atoms-in-molecules theory of Bader and the Becke–Edgecombe
electron localization function. Bond critical points are localized by means of the analysis of the electron density gradient
field, ∇ρ(r), and the electron localization function gradient field, ∇η(r). The values of the electron density properties, i.e., electron density, ρ(r), Laplacian of the electron density, ∇2ρ(r), and electron localization function, η(r), allow the nature of the bonds to be characterized, and linear correlation is found for the results obtained in both gradient
fields. Vanadium-oxygen interactions are characterized as unshared-electron interactions, and linear correlation is observed
between the electron density properties and the V–O bond length. In contrast, O2 units involve typical shared-electron interactions, as for the dioxygen molecule. Four different vanadium–oxygen interactions
are found and characterized: a molecular O2 interaction, a peroxo O2
2− interaction, a superoxo O2
− interaction and a side-on O2
− interaction.
Received: 15 October 2001 / Accepted: 30 January 2002 / Published online: 24 June 2002 相似文献
16.
Rois Benassi 《Theoretical chemistry accounts》2001,106(4):259-263
In order to calculate more accurately the enthalpies of formation, ΔH
f°(298 K), for large molecules using the CBS-4M method, a new formulation of the empirical higher-level correction to the energy
is proposed: ΔE=a|S|2
i
i
I
i
i
+b(n
α+n
β)+cΔ<S
2>+Σn
i
d
i
. The new methodology (CBS-4MB) applied to a set of 114 molecules of different size significantly decreases the mean absolute
deviation from 3.78 to 2.06 kcal/mol.
Received: 7 February 2001 / Accepted: 5 April 2001 / Published online: 13 June 2001 相似文献
17.
Bernhard Metz Marcus Schweizer Hermann Stoll Michael Dolg Wenjian Liu 《Theoretical chemistry accounts》2000,104(1):22-28
A relativistic pseudopotential of the energy-consistent variety simulating the Tl21+ (1s– 4f) core has been generated by adjustment to multiconfiguration Dirac–Hartree–Fock data based on the Dirac–Coulomb–Breit Hamiltonian.
Valence ab initio calculations using this pseudopotential have been performed for atomic excitation energies and for spectroscopic
constants of the X0+ and A0+ states of TlX (X = F, Cl, Br, I). Comparison is made to experiment and to four-component density functional results.
Received: 22 June 1999 / Accepted: 5 August 1999 / Published online: 15 December 1999 相似文献
18.
The influence of collector structure on interaction with metal cations was modelled by computational ab initio methods. The
interaction energies were calculated between metal ions (Cu+, Cu2+, Zn2+ and Pb2+) and selected collector anions: ethyl xanthate, ethyl trithiocarbonate, dithiobutyric acid, ethyl dithiocarbamate, diethyl
dithiocarbamate, diethylphosphinecarbodithioic acid and diethoxyphosphinecar bodithioic acid. The strongest interaction was
found with diethyl dithiocarbamate. The results give qualitative information on the effect of the collector structure on the
initial adsorption steps on sulphide mineral flotation.
Received: 25 September / Accepted: 11 October 2001 / Published online: 22 March 2002 相似文献
19.
A method applying ab initio direct dynamics has been utilized in studying the hydrogen abstraction reaction HCN + OH → CN + H2O. The geometries of the reactants, products, and the transition state have been optimized at the QCISD/6-311G(d, p) level.
Single-point energies were further evaluated at the QCISD(T)/6-311+G(2df, 2p)//QCISD/6-311G(d, p) level. The barrier heights
for the forward and reverse reactions were predicted to be 15.95 and 7.51 kcal mol−1 at the QCISD(T)/6-311 + G(2df, 2p)//QCISD/6-311G(d, p) level, respectively. The reaction rate constants were calculated in
the temperature range from 298 to 4,000 K using the canonical variational transition-state theory with a small-curvature tunneling
correction. The results of the calculation show that the theoretical rate constants are in good agreement with experimental
data over the measured temperature range of 400–2,600 K.
Received: 18 August 2002 / Accepted: 30 August 2002 / Published online: 20 November 2002
Acknowledgements. Our thanks are due to D.G. Truhlar for providing the POLYRATE 8.2 program. This work was supported by the National Science
Foundation of China. We also thank D.C. Fang and Y. M. Xie for their valuable help, and P.R. Yan for reading our paper.
Correspondence to: Q. S. Li e-mail: qsli@mh.bit.edu.cn 相似文献
20.
Complete active space self-consistent-field (CASSCF) and multiconfigurational second-order perturbation theory (CASPT2) calculations
in conjunction with the ANO-L basis set were performed to investigate systematically the low-lying electronic states of HNCS
and its ions in C
s
symmetry. Our highly accurate calculation indicated that theoretically determined geometric parameters and harmonic vibrational
frequencies for the ground-state X
1A′ are in good agreement with observed experimental data. The geometry of triplet HNCS is clearly favored C
1
symmetry, and the relative energy is predicted to be 3.000 eV (69.2 kcal/mol). The vertical transition energies for the selected
excited states of HNCS were calculated at CASSCF/CASPT2/ANO-L level of theory based on CASSCF optimized geometry. Except for
a few linear states of X
2Π (12A′, 12A″), 14Σ− (14A″), and 12Σ+ (32A′) states of HNCS+, our results confirmed that the majority of excited states are twisted trans-bend structures. The existence of bound excited
anion states has been found for the first time in HNCS−. A more elaborate examination of ionization potential of HNCS (AIP, VIP) than previous reports has been presented. 相似文献