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1.
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
2.
The B3LYP/6-311G(d) and CCSD(T)/6-311G(2df) (single-point) methods have been used to investigate the singlet potential energy
surface of C2NP, in which seven stationary isomers and seventeen interconversion transition states are involved. At the final CCSD(T)/6-311G(2df)//B3LYP6-311G(d)
level with zero-point vibrational energy correction the lowest-lying isomer is a linear NCCP followed by two linear CNCP isomers
at 23.9 and CCNP at 65.8 kcal mol−1, respectively. The three isomers are kinetically very stable towards both isomerization and dissociation, and CCNP is even
more kinetically stable than CNCP – by 14.3 kcal mol−1 despite its high energy. Further comparative calculations were performed at the QCISD and QCISD(T) levels with the 6-311G(d)
and 6-311G(2d) basis sets to obtain more reliable structures and spectroscopy for the three isomers. The calculated bond lengths,
rotational constant, and dipole moment for NCCP were in close agreement with the experimentally determined values. Finally,
similarities and discrepancies between the potential energy surface of C2NP and those of the analogous species C2N2 and C2P2 were compared. The results presented in this paper might be helpful for future identification of the two still unknown yet
kinetically very stable isomers CNCP and CCNP, both in the laboratory and in interstellar space.
Received: 3 January 2001 / Accepted: 6 June 2001 / Published online: 30 October 2001 相似文献
3.
Kouichi Takeshita 《Theoretical chemistry accounts》1999,101(5):343-351
Ab initio calculations have been performed to study the molecular structures and the vibrational levels of the first ionic
states of vinyl fluoride, vinyl chloride, trifluoroethylene, and trichloroethylene. The equilibrium molecular structures and
vibrational modes of these states are presented. The theoretical ionization intensity curves including the vibrational structures
are also presented and compared with the photoelectron spectra.
Received: 11 September 1998 / Accepted: 13 October 1998 / Published online: 1 February 1999 相似文献
4.
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
5.
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
6.
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
7.
Daniel M. Chipman 《Theoretical chemistry accounts》2002,107(2):80-89
Alternative ways are examined for representing a reaction field to treat the important effects of long-range electrostatic
interaction with a solvent in electronic structure calculations on the properties of a solute. Several extant boundary element
methods for approximate representation of the solvent reaction field in terms of surface charge distributions are considered,
and analogous new methods for approximate representation in terms of surface dipole distributions are introduced. Illustrative
computational results are presented on representative small neutral and ionic solutes to evaluate the relative accuracy of
various methods.
Received: 2 July 2001 / Accepted: 10 September 2001 / Published online: 19 December 2001 相似文献
8.
Ab initio calculations have been performed to investigate the state transition in photoinduced electron transfer reactions
between tetracyanoethylene and biphenyl as well as naphthalene. Face-to-face conformations of electron donor–acceptor (EDA)
complexes were selected for this purpose. The geometries of the EDA complexes were determined by using the isolated optimized
geometries of the donor and the acceptor to search for the maximum stabilization energy along the center-to-center distance.
The correction of interaction energies for basis set superposition error was considered by using counterpoise methods. The
ground and excited states of the EDA complexes were optimized with complete-active-space self-consistent-field calculations.
The theoretical study of the ground state and excited states of the EDA complex in this work reveals that the S1 and S2 states of the EDA complexes are charge–transfer (CT) excited states, and CT absorption which corresponds to the S0→S1 and S0→S2 transitions arise from π−π* excitation. On the basis of an Onsager model, CT absorption in dichloromethane was investigated by considering the solvent
reorganization energy. Detailed discussions on the excited state and on the CT absorptions were made.
Received: 30 April 2001 / Accepted: 18 October 2001 / Published online: 9 January 2002 相似文献
9.
The hydrogen-ion molecule has been used as a test system for the application of the Schr?dinger–Riccati formulation to molecular
calculations. Some of the points discussed are the characteristics (quasiconstancy of the local energies, size, number of
points) of the sampling region to be chosen, the dependence on the starting function, the precision of the calculations, and
the excellent behaviour of the predicted function (by comparison to an accurate function).
Received: 1 May 2001 / Accepted: 25 July 2001 / Published online: 11 October 2001 相似文献
10.
11.
Methods are described to incorporate solvent reaction field effects into solute electronic structure calculations. Included
are several old and new approaches based on approximate solutions of Poisson's equation through boundary element methods,
wherein the solutions are represented in terms of certain apparent surface charge or apparent surface dipole distributions.
Practical algorithms to set up and solve the requisite equations are described and implemented in a new general reaction field
computer program. Illustrative computational results are presented to show the performance of the program.
Received: 2 July 2001 / Accepted: 11 September 2001 / Published online: 19 December 2001 相似文献
12.
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
13.
14.
Sequential Monte Carlo/quantum mechanical calculations are performed to study the solvent effects on the electronic absorption
spectrum of formamide (FMA) in aqueous solution, varying from hydrogen bonds to the outer solvation shells. Full quantum-mechanical
intermediate neglect of differential overlap/singly excited configuration interaction calculations are performed in the supermolecular
structures generated by the Monte Carlo simulation. The largest calculation involves the ensemble average of 75 statistically
uncorrelated quantum mechanical results obtained with the FMA solute surrounded by 150 water solvent molecules. We find that
the n → π* transition suffers a blueshift of 1,600 cm−1 upon solvation and the π → π* transition undergoes a redshift of 800 cm−1. On average, 1.5 hydrogen bonds are formed between FMA and water and these contribute with about 20% and about 30% of the
total solvation shifts of the n → π* and π → π* transitions, respectively. The autocorrelation function of the energy is used
to sample configurations from the Monte Carlo simulation, and the solvation shifts are shown to be converged values.
Received: 14 March 2002 / Accepted: 3 April 2002 / Published online: 24 June 2002 相似文献
15.
Kinetic isotope effects, KIEs, for hydrogen abstraction from C2H6 and C2D6 by chlorine atom have been studied by the dual-level direct dynamics approach. A low-level potential energy surface is obtained
with the MNDO-SRP method. High-level structural properties of the reactants, transition state, and products were obtained
at the MP2 level with the cc-pVDZ, aug-cc-pVDZ, and the cc-pVTZ basis sets. Using the variational transition state theory
with microcanonical optimized multidimensional tunneling, the values of deuterium KIE, at 300 K, range from 2.28 to 3.27,
in good agreement with the experimental values (2.69–5.88).
Received: 6 June 2001 / Accepted: 12 July 2001 / Published online: 19 November 2001 相似文献
16.
Shigeyoshi Yamamoto Hiroshi Tatewaki Osamu Kitao Geerd H.F. Diercksen 《Theoretical chemistry accounts》2001,106(4):287-296
The Rydberg character of the excited states of free-base porphin (FBP) has been investigated by the ab initio configuration
interaction singles (CIS) method and the state-averaged complete-active-space self-consistent-field method. Double-zeta basis
sets augmented with s, p, and d Rydberg functions and d polarization functions have been employed. Two types of molecular
orbitals sets, the restricted Hartree–Fock molecular orbitals obtained for the ground state (1A
g
) and for the cation state (2A
u
), have been used in the CIS calculations. All the calculations show that Rydberg-type excitations play important roles especially
in the N bands. In this article we propose applying the model of a perturbed Rydberg series to interpret the excited states
of FBP. By using this model, we have succeeded in analyzing the characteristics of the excited states as well as the experimental
oscillator strengths, which have considerable magnitude even in the higher excited states.
Received: 27 November 2000 / Accepted: 11 April 2001 / Published online: 27 June 2001 相似文献
17.
H. Strømsnes S. Jusuf A. Bagatur'yants O. Gropen U. Wahlgren 《Theoretical chemistry accounts》2001,106(5):329-338
The convergence of chemisorption energy for hydrogen and oxygen on gold clusters is studied. Two theoretical approaches have
been employed; wavefunction methods at the self-consistent-field second–order M?ller–Plesset level and density functional
theory and the two methods are compared. Relativistic effective core potentials exploited in the former approach were developed
in this work.
Received: 25 October 1999 / Accepted: 21 February 2001 / Published online: 11 October 2001 相似文献
18.
Zhongfang Chen Jerzy Cioslowski Niny Rao David Moncrieff Michael Bühl Andreas Hirsch Walter Thiel 《Theoretical chemistry accounts》2001,106(5):364-368
For all isolated pentagon isomers of the fullerenes C60–C86 with nonzero HOMO–LUMO gap and for one nonclassical C72 isomer (C2
v
), endohedral chemical shifts have been computed at the GIAO-SCF/3-21G level using B3LYP/6-31G* optimized structures. The
experimental 3He NMR signals are reproduced reasonably well in cases where assignments are unambiguous (e.g. C60, C70 and C76). On the basis of the calculated thermodynamic stability order and the comparison between the computed and experimental 3He chemical shifts, the assignments of the observed 3He NMR spectra are discussed for all higher fullerenes, and new assignments are proposed for one C82 and one C86 isomer (C82:3 and C86:17). The calculated helium chemical shifts also suggest the reassignment of the δ(3He) resonances of two C78 isomers.
Received: 26 March 2001 / Accepted: 10 May 2001 / Published online: 11 October 2001 相似文献
19.
Amy J. Austin Michael J. Frisch John A. Montgomery George A. Petersson 《Theoretical chemistry accounts》2002,107(3):180-186
An overlap criterion is defined that connects the identification of core orbitals in a molecular system, which can be problematic,
to that in isolated atoms, which is well defined. This approach has been tested on a variety of troublesome systems that have
been identified in the literature, including molecules containing third-row main-group elements, and is shown to remove errors
of up to 100 kcal/mol arising from an inconsistent treatment of core orbitals at different locations on a potential-energy
surface. For some systems and choices of core orbitals, errors as large as 19 kcal/mol can be introduced even when consistent
sets of orbitals are frozen, and the new method is shown to identify these cases of substantial core–valence mixing. Finally,
even when there is limited core–valence mixing, the frozen-core approximation can introduce errors of more than 5 kcal/mol,
which is much larger than the presumed accuracy of models such as G2 and CBS-QB3. The source of these errors includes interatomic
core–core and core–valence dispersion forces.
Received: 31 August 2001 / Accepted: 11 October 2001 / Published online: 9 January 2002 相似文献
20.
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