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1.
Frank Jensen 《Theoretical chemistry accounts》1998,99(5):295-300
A total of 36 stationary points have been located on the H2CO potential energy surface by means of gradient extremal following. These 36 points are believed to represent all the important
stationary points on this surface. There is no indication that the structure of the surface becomes less complicated as the
size of the basis set is enlarged at the Hartree-Fock level of theory, but many of the second- and third-order saddle points
disappear when electron correlation is introduced. Of the ten first-order saddle points (transition structures) located, the
majority have reaction paths entering the associated minima in a side-on approach, i.e. these cannot be located by uphill
walking from the minimum.
Received: 5 February 1998 / Accepted: 21 May 1998 / Published online: 29 July 1998 相似文献
2.
A homotopy method is presented that locates both minimizers and saddle points of energy functions in an efficient manner.
In contrast to other methods, it makes possible the exploration of large parts of potential energy surfaces. Along a homotopy
path stationary points of odd and even order occur alternately. A path tracing procedure requiring only gradients and at most
one evaluation of the Hessian matrix is given. Test results on a model potential and three MINDO/3 potentials are reported.
Received: 6 May 1996 / Accepted: 2 April 1998 / Published online: 23 June 1998 相似文献
3.
Ramon Crehuet Josep Maria Bofill Josep Maria Anglada 《Theoretical chemistry accounts》2002,107(3):130-139
The mathematical structure of the reduced-gradient-following (RGF) path introduced by Quapp et al. (1988 J. Comput. Chem. 19:1087) is reviewed and analyzed. We report two new algorithms to evaluate the RGF path. The RGF path is also compared mathematically
and computationally with the gradient extremals path. An example of the evaluation of the RGF path is also reported.
Received: 21 May 2001 / Accepted: 27 September 2001 / Published online: 9 January 2002 相似文献
4.
High-level ab initio electronic structure theories have been applied to investigate the detailed reaction mechanism of the
spin-forbidden reaction CH(2∏) + N2 → HCN + N(4S). The G2M(RCC) calculations provide accurate energies for the intermediates and transition states involved in the reaction,
whereas the B3LYP/6-311G(d,p) method overestimates the stability of some intermediates by as much as about 10 kcal/mol. A few new structures have been
found for both the doublet and quartet electronic states, which are mainly involved in the dative pathways. However, due to
the higher energies of these structures, the dominant mechanism remains the one involving the C
2 intersystem-crossing step. The C
2 minima on the seam of crossing (MSX) structures and the spin-orbit coupling between the doublet and quartet electronic states
are rather close to those found in previous studies. Vibrational frequencies orthogonal to the normal of the seam which have
been applied in a separate publication to calculate the rate of the CH(2∏) + N2 → HCN + N(4S) reaction with a newly proposed nonadiabatic transition-state theory for spin-forbidden reactions have been calculated at
the MSX from first principles.
Received: 23 June 1998 / Accepted: 21 September 1998 / Published online: 8 February 1999 相似文献
5.
An analysis of a model molecular oscillator is presented: a vibrating diatomic molecule carrying N
0 electrons. The energy derivatives over the number of electron (N) and the deformation (Q), ∂
n
/∂N
n
and ∂
n
/∂Q
n
have been analyzed up to second order (n=2), including the appropriate mixed derivatives. The effect of coupling between distortion of the electron density induced
by ΔN and the vibrational deformation of the molecule has been studied. Anharmonicity of the oscillator has been shown to be a
possible result of that coupling; new relations between the parameters characterizing the anharmonicity of the oscillator
and the energy derivatives at density functional theory level have been obtained. Ab initio calculations for a set of diatomic molecules have been performed, yielding values for all the derivatives discussed and demonstrating
the effect of coupling with vibrations.
Received: 1 June 2000 / Accepted: 20 October 2000 / Published online: 21 March 2001 相似文献
6.
The hierarchy of the electron localization basins is a powerful tool of analysis of the bonding in molecules and solids within
the “elfological” framework. It is a generalization of the molecular isodensity contour analysis originally proposed by Mezey.
In this approach the basins are ordered with respect to the electron localization function values at the critical points which
determine the reduction of the reducible localization domains. The procedure enabling the corresponding tree diagrams to be
built is described and it is shown how the method can be used as a generator of mathematical definitions of chemical concepts.
The possibility offered by this simple tool is illustrated by a study of the VO
x
and VO
x
+ (x=1–4) oxides in their ground state and in some excited states.
Received: 20 July 2000 / Accepted: 20 October 2000 / Published online: 23 January 2001 相似文献
7.
Geometries and stabilization energies of various simple H-bonded complexes (water dimer, hydrogen fluoride dimer, formamide
dimer, formic acid dimer) have been determined by a gradient optimization that eliminates the basis set superposition error
(BSSE) by the counterpoise (CP) method in each gradient cycle as well as by the standard gradient optimization. Both optimization
methods lead to different potential energy surfaces (PES). The difference depends on the theoretical level used and is larger
if correlation energy is considered. Intermolecular distances from the CP-corrected PES are consistently longer, and this
difference might be significant (∼0.1 ?); also angular characteristics determined from both surfaces differ significantly.
Different geometries were obtained even when passing to larger basis sets (aug-cc-pVDZ). The standard optimization procedure
can result in a completely wrong structure. For example, the “quasi-linear” structure of the (HF)2 (global minimum) does not exist at the standard MP2/ 6-31G** PES (where only cyclic structure was detected) and is found
only at the CP-corrected PES. Stabilization energies obtained from the CP-corrected PES are always larger than these from
the standard PES where the BSSE is added only a posteriori for the final optimized structure; both energies converge only
when passing to a larger basis set (aug-cc-pVDZ).
Received: 11 March 1998 / Accepted: 19 June 1998 / Published online: 4 September 1998
RID="
ID=" <E6>Acknowledgements.</E6> The project was supported by the Grant Agency of the Czech Republic (Grant No. 203/98/1166).
RID="
ID=" <E5>Correspondence to</E5>: P. Hobza 相似文献
8.
The chemical reactions between (−)-deprenyl and ·OH or ·OOH were studied using molecular orbital theory, with N,N-dimethylpropargylamine as a model. (−)-Deprenyl was confirmed to be a good radical scavenger. The active site was the acetylenic
part and ·OH- or ·OOH was trapped on either acetylenic carbon. The activation energies were about 10–20 kcal/mol. The resulting ·OH- or ·OOH-adducts, still radicals, trapped further radicals on the remaining carbon of the acetylenic part. The final double trapping
products were at extraordinarily lower energy levels than the original reactants by 50–70 kcal/mol. The secondary transition
states were not detected, suggesting that the reactions occurred at once or in a cascade. Some results with the model system
were verified by the results with the real (−)-deprenyl system.
Received: 6 October 1999 / Accepted: 5 March 2000 / Published online: 21 June 2000 相似文献
9.
E. L. Cavalieri E. C. Vauthier A. Cossé-Barbi S. Fliszár 《Theoretical chemistry accounts》2000,104(3-4):235-239
Self-consistent-field computations shed light on two relevant conformations of deoxyadenosine (dA) and deoxyguanosine (dG):
one with a pseudoequatorial C1′N9 glycosyl bond and the other, a slightly more stable one, with its C1′N9 bond in a bisectional orientation. In dA, both the N3 and N7 nitrogens are plausible sites for electrophilic attack, but only N7 is a plausible site in dG. The addition of H+, CH3
+, C2H5
+ or tert-C4H9
+ onto N7 does not provoke notable structural modifications and leaves the base of dA and dG in an antiperiplanar (or nearly antiperiplanar)
position with respect to the sugar C1′O4′ bond, but N3 additions cause the base to adopt a synperiplanar or strongly chiral position. This produces strong interactions between
the purine and deoxyribose moieties, whose relief could aid the eventual cleavage of the glycosyl bond of dA. Addition of
a radical cation onto N7 reduces the dissociation energy of the glycosyl bond by an estimated 8 kcal mol−1 in dA and 4 kcal mol−1 in dG – a bond weakening likely to concur to a depurination of DNA induced by radical cations.
Received: 13 September 1999 / Accepted: 3 February 2000 / Published online: 21 June 2000 相似文献
10.
The nature of bonding in several hypervalent molecules was analyzed at the ab initio SCF level using the recently proposed methodology based on the analysis of domain-averaged Fermi holes. The results of the
analysis demonstrate that, for sufficiently flexible basis sets, the expansion of the valence shell does indeed take place
for second row central atoms in PF5, SF4, and SF6. On the other hand, no such expansion was observed for the first row N atom in NF5.
Received: 1 June 2000 / Accepted: 11 October 2000 / Published online: 23 January 2001 相似文献
11.
Myung-Hwan Whangbo 《Theoretical chemistry accounts》2000,104(3-4):252-256
The size-consistent self-consistent matrix dressing method has been applied on an open-shell single-configuration reference
state. Once the reference state is converged, several low-lying roots can be obtained for the dressed configuration interaction
(CI) matrices of appropriate symmetry. The CI matrices were built with a complete-active-space singles and doubles CI method
in order to deal properly with multiconfiguration excited states. The vertical ionization and ionization–excitation transitions
are obtained from the difference to the closed shell ground-state energy of the neutral molecule. The method has been applied
to NH+
3 and N+
2 using atomic natural orbital basis sets and state-average adapted molecular orbitals. Two 2A1 states, very similar and showing great mixing of the (2a
l
−1) and (3a
l
−25a
l
1) determinants, can be assigned to the broad asymmetric band at 27.6 ± 2 eV in the photoelectron spectrum of NH3. The possible contribution of a 2Π
g
(3σ
g
−21π
g
1) state to the A shake-up peak of N2 at 24.6 eV is also discussed. Other states, doublets and quadruplets, are reported for both systems up to 30 eV for NH3 and 37 eV for N2.
Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000 相似文献
12.
Bernd Hartke 《Theoretical chemistry accounts》1998,99(4):241-247
By an application to small silicon clusters Si
N
(with N = 4,5,7,10) it is shown that truly global geometry optimization on an ab initio or density functional theory level can be achieved, at a computational cost of approximately
1–5 traditional local optimization runs (depending on cluster size). This extends global optimization from the limited area
of empirical potentials into the realm of ab initio quantum chemistry.
Received: 24 February 1998 / Accepted: 6 March 1998 / Published online: 17 June 1998 相似文献
13.
The effect of the inclusion of the exact exchange into self-interaction corrected generalized gradient approximation density
functional theory (GGA-DFT) for the simplest hydrogen abstraction reaction, H + H2 → H3 → H2 + H, is presented using a triple-zeta augmented 6-311++G(d,3pd) basis set. The introduction of the self-interaction correction has a considerably larger effect on molecular geometry and
vibrational frequencies than the inclusion of the exact exchange. We investigate the influence of the self-interaction error
on the shape of the potential energy surface around the transition state of the hydrogen abstraction reaction. The decomposition
of the self-interaction error into correlation and exchange parts shows that the exchange self-interaction error is the main
component of the energy barrier error. The best agreements with the experimental barrier height were achieved by self-interaction
corrected B3LYP, B-LYP and B3PW functionals with errors of 1.5, 2.9 and 3.0 kcal/mol, respectively.
Received: 13 August 1997 / Accepted: 14 November 1997 相似文献
14.
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
15.
Roland H. Stote 《Theoretical chemistry accounts》2001,106(1-2):128-136
Geometric properties of the RGD sequence in a data set of protein crystal and NMR structures deposited in the Protein Data
Bank were examined to identify structural characteristics that are related to cell adhesion activity. Interatomic distances
and dihedral angles are examined. These geometric measures are then used in an analysis of the conformations of the RGDW and
DRGDW peptides obtained from molecular dynamics simulations (Stote RH, et al. (2000) J Phys ChemB 104:1624). This analysis leads to the suggestion that differences in the accessible conformations contribute to the difference
in biological activity between the RGDW and the DRGDW peptides.
Received: 15 August 2000 / Accepted: 4 October 2000 / Published online: 21 March 2001 相似文献
16.
Maria Bykhovskaia Boris Gelmont Tatiana Globus Dwight L. Woolard Alan C. Samuels Tap Ha Duong Krystyna Zakrzewska 《Theoretical chemistry accounts》2001,106(1-2):22-27
We present a computational method which couples normal mode analysis in internal coordinates of a molecule with very far
IR spectroscopy. The analytical expression for the dependence of IR absorption on frequency incorporates frequencies and optical
activities of each normal mode. In order to predict far-IR spectra of a molecule we evaluate the optical activity of each
normal mode. This optical activity is determined by the vibration amplitude of the dipole moment produced by a normal mode.
We calculated normal modes of DNA double-helical fragments (dA)12 · (dT)12 and (dA-dT)6 · (dA-dT)6 and evaluated their optical activities. These were found to be very sensitive to the DNA base-pair sequence. The positions
of the resonance peaks in the calculated absorption spectrum of (dA)12 · (dT)12 are in a good agreement with those obtained by Fourier transform IR spectroscopy (Powell JW et al. 1987 Phys Rev A 35: 3929–3939).
Received: 20 June 2000 / Accepted: 5 January 2001/ Published online: 3 May 2001 相似文献
17.
Sergio Martí Juan Andrés Vicent Moliner Estanislao Silla Iñaki Tuñón Juan Bertrán 《Theoretical chemistry accounts》2001,105(3):207-212
Two different transition structures (TSs) have been located and characterized for the chorismate conversion to prephenate
in Bacillus subtilis chorismate mutase by means of hybrid quantum-mechanical/molecular-mechanical (QM/MM) calculations. GRACE software, combined
with an AM1/CHARMM24/TIP3P potential, has been used involving full gradient relaxation of the position of ca. 3300 atoms.
These TSs have been connected with their respective reactants and products by the intrinsic reaction coordinate (IRC) procedure
carried out in the presence of the protein environment, thus obtaining for the first time a realistic enzymatic reaction path
for this reaction. Similar QM/MM computational schemes have been applied to study the chemical reaction solvated by ca. 500
water molecules. Comparison of these results together with gas phase calculations has allowed understanding of the catalytic
efficiency of the protein. The enzyme stabilizes one of the TSs (TSOHout) by means of specific hydrogen bond interactions, while the other TS (TSOHin) is the preferred one in vacuum and in water. The enzyme TS is effectively more polarized but less dissociative than the
corresponding solvent and gas phase TSs. Electrostatic stabilization and an intramolecular charge-transfer process can explain
this enzymatically induced change. Our theoretical results provide new information on an important enzymatic transformation
and the key factors responsible for efficient selectivity are clarified.
Received: 25 March 2000 / Accepted: 7 August 2000 / Published online: 23 November 2000 相似文献
18.
Wolfgang Quapp Michael Hirsch Dietmar Heidrich 《Theoretical chemistry accounts》1998,100(5-6):285-299
This paper serves for the better understanding of the branching phenomenon of reaction paths of potential energy hypersurfaces
in more than two dimensions. We apply the recently proposed reduced gradient following (RGF) method for the analysis of potential
energy hypersurfaces having valley-ridge inflection (VRI) points. VRI points indicate the region of possible reaction path
bifurcation. The relation between RGF and the so-called global Newton search for stationary points (Branin method) is shown.
Using a 3D polynomial test surface, a whole 1D manifold of VRI points is obtained. Its relation to RGF curves, steepest descent
and gradient extremals is discussed as well as the relation of the VRI manifold to bifurcation points of these curves.
Received: 8 July 1998 / Accepted: 24 August 1998 / Published online: 23 November 1998 相似文献
19.
We propose a method to locate saddle points that is based on the interplay between the driving coordinate and the restricted
quasi-Newton algorithm. The method locates the transition state using a reduced potential-energy surface. The reduced potential-energy
surface is characterized by the set of driving coordinates. The proposed algorithm starts at a point on the surface that is
slightly perturbed from either reactant or product and, in principle, converges to the transition state. Finally we give a
special type of update Hessian matrix formula that should be applied in optimizations carried out on reduced potential-energy
surfaces.
Received: 29 September 2000 / Accepted: 3 January 2001 / Published online: 3 April 2001 相似文献
20.
Yu. A. Borisov 《Russian Chemical Bulletin》2000,49(8):1327-1331
Protonated forms of the molecules of ethylene derivatives with the general formula C2X2Y2 (X=Y=H) (1), F (2), CH3 (3) CH3 (4); X=F, Y=H:cis-(5)trans- (6)) were calculated by theab initio MP2/6-31 G* method with full geometry optimization. The minima and saddle points located on the potential energy surface (PES) of the
protonated ethylene molecule correspond to the stationary states and transition states of proton migration, respectively.
The stationary states are characterized by a nonclassical geometry of carbocations similar to that of π-complexes, whereas
the transition states have a classical structure. Unlike1, the carbocations of molecules2–6 have the classical structure. The saddle points on the PES of the ethylene derivatives correspond to the structures of the
π-complex type, which are the transition states of proton migration between the C atoms of the ethylene bond. The barrier
to rotation about, the C−C bond depends essentially on the substituent nature.
Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1333–1337, August, 2000. 相似文献