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1.
Martin Albrecht Peter Reinhardt Jean-Paul Malrieu 《Theoretical chemistry accounts》1998,100(1-4):241-252
A size-consistent ab initio formalism to calculate correlation corrections to ionization potentials as well as electron affinities
of periodic systems is presented. Our approach is based on a Hartree-Fock scheme which directly yields local orbitals without
any a posteriori localization step. The use of local orbitals implies non-zero off-diagonal matrix elements of the Fock operator,
which are treated as an additional perturbation and give rise to localization diagrams. Based on the obtained local orbitals,
an effective Bloch Hamiltonian is constructed to second order of perturbation theory with all third-order localization diagrams
included. In addition, the summation of certain classes of diagrams up to infinite order in the off-diagonal Fock elements
as well as the Epstein-Nesbet partitioning of the full Hamiltonian are discussed. The problem of intruder states, frequently
encountered in many-body perturbation theory, is dealt with by employing the theory of intermediate Hamiltonians. As model
systems we have chosen cyclic periodic structures up to an oligoethylene ring in double-zeta basis; however, the theory presented
here straightforwardly carries over to infinite periodic systems.
Received: 30 April 1998 / Accepted: 27 July 1998 / Published online: 7 October 1998 相似文献
2.
Polystyrene/styrene–divinylbenzene copolymer composite particles with different cross-linking densities were produced by
seeded copolymerization for (styrene/divinylbenzene)-swollen polystyrene particles prepared by utilizing the dynamic swelling
method (DSM) which was proposed by the authors in 1991. Using the cross-linked, composite particles as seeds, styrene-adsorbed
(swollen) composite particles having snowman shapes were prepared by the DSM. With a decrease in the cross-linking density
in the composite particles, the volume of the composite particle which was embedded in a spherical styrene phase in the snowman-shaped,
styrene-adsorbed particle increased and the contact angle of the styrene phase on the composite particle decreased. In the
DSM process, the absorption stage of styrene in the composite particles and the adsorption stage thereon were clearly observed.
This suggests that the cross-linking density of the composite particles greatly affects the morphology of the snowman-shaped
particles.
Received: 13 December 2000 Accepted: 14 March 2001 相似文献
3.
We studied the adsorption of two neutral polymers [poly(vinyl pyrrolidone) and poly(vinyl alcohol) (PVA)] on negatively charged
liposomes composed of 25:2:3 (molar ratio) soy lecithin/dicetyl phosphate/cholesterol.The liposomes were prepared in buffered
solution at pH 7.4 and were mixed with the solution of the polymers in the desired polymer/lipid ratios. Adsorption was measured
by determination of the equilibrium bulk concentration of the polymer. Protamine hydrochloride was used to aggregate the liposomes
with polymers adsorbed on their surface and to facilitate their separation from the equilibrium bulk solution. In the case
of PVA, quantitative adsorption measurements with a specific reagent were possible. Adsorption isotherms were recorded at
25 ± 0.2 °C. It was concluded that adsorbed and nonadsorbed PVA molecules are in equilibrium even at low polymer/lipide ratios.
The results were confirmed by dynamic laser light scattering, X-ray diffraction and thermal activity monitoring experiments.
Received: 13 October 2000 Accepted: 8 March 2001 相似文献
4.
Effect of amorphous precipitated silica on the properties and structure of poly(p-phenylene sulfide)
T. Jesionowski K. Bula J. Jurga A. Krysztafkiewicz 《Colloid and polymer science》2001,279(10):983-989
Using a precipitation technique, silicas were obtained from sodium metasilicate solution employing an acidic agent. Alcohol
solutions were used in the process of production of highly dispersed silicas, which resulted in partial blocking of the silica
surface silanol groups. Moreover, studies on morphology and microstructure using transmission electron microscopy and scanning
electron microscopy were performed. The size distributions of primary particles and aggregate and agglomerate structures were
determined using a ZetaPlus instrument using the dynamic light scattering method. The structure and molecular dynamics of
the nanocomposite, consisting of poly (p-phenylene sulfide) (PPS) and of the precipitated silica, were studied using atomic force microscopy and nuclear magnetic
resonance. It was proved that during annealing the fragmentation of PPS agglomerates takes place. This phenomena probably
resulted from repulsion forces existing between agglomerates and aggregates. Fragmentation in the polymer network probably
resulted from repulsion forces between agglomerates and smaller aggregates.
Received: 7 November 2000 Accepted: 5 April 2001 相似文献
5.
Christopher J. Parkinson Paul M. Mayer Leo Radom 《Theoretical chemistry accounts》1999,102(1-6):92-96
Stabilization energies for the 1-cyanovinyl radical (CH2=CCN) have been calculated using a variety of conventional ab initio (M?ller–Plesset, quadratic configuration interaction
and coupled-cluster) and density functional theory (B-LYP, B3-LYP) procedures, as well as with a range of compound methods.
Compared with a high-level benchmark value (that predicts a stabilization energy of 17.1 kJ mol−1), UMP2 and UMP4 give the wrong sign and magnitude of the stabilization energy (both methods predicting desta- bilization
instead of stabilization), while B-LYP and B3-LYP overestimate the degree of stabilization. The RMP2, RMP4, QCISD(T) and CCSD(T)
techniques, and several, but not all, variants of G2 and CBS theories give radical stabilization energies in good agreement
with the benchmark value.
Received: 15 June 1998 / Accepted: 19 August 1998 / Published online: 15 February 1999 相似文献
6.
I. Flamant J. G. Fripiat J. Delhalle Frank E. Harris 《Theoretical chemistry accounts》2000,104(5):350-357
Formulas are presented for restricted Hartree–Fock (RHF) calculations on systems with periodicity in one dimension using
a basis set of contracted spherical Gaussians. Applying Fourier-space and Ewald-type methods, all lattice sums appearing in
the formulation have been brought to forms exhibiting accelerated convergence. Calculations have been carried out for infinite
chains of Li2 molecules and a poly(oxymethylene) chain. The methods used here yield results that are far more precise than corresponding
direct-space calculations and for the first time show the vanishing of the RHF density of states at the Fermi level for situations
of partial band occupancy. Our initial computational implementation was about 5 times slower than the fastest direct-space
RHF code, but improvements in special-function evaluations and numerical integrations over the Brillouin zone are shown to
remove this disparity in computing speed.
Received: 20 August 1999 / Accepted: 17 January 2000 / Published online: 5 June 2000 相似文献
7.
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
8.
Xianyang Chen Chongde Li Tao Wu Tianyang Yao Guanzhi Ju 《Theoretical chemistry accounts》1998,99(4):272-276
Ab initio molecular electronic structure methods have been used to study the relative stability of the planar inorganic ring
(HAlNH)n (n = 2–4) during homodesmotic and monomer polymerization reactions. Optimized geometries, frequencies and energies through
restricted Hartree-Fock/6-31G* are reported, and energies at the self-consistent field optimized geometries including M?ller-Plesset
fourth perturbation theory with single, double and quadruple excitation (MP4SDQ) corrections are also reported for both reactions.
Homodesmotic reactions with MP4SDQ −28.5 kcal/mol for (AlN)2, 1.9 kcal/mol for (AlN)3 and −0.97 kcal/mol for (AlN)4. On analysing a π-molecular orbitals diagram, only one, three and three strongly bonding π-molecular orbitals exist for the
planar four-, six- and eight-membered AlN rings, respectively.
Received: 9 March 1998 / Accepted: 19 March 1998 / Published online: 23 June 1998 相似文献
9.
10.
11.
S. L. Koontz R. V. Devivar W. J. Peltier J. E. Pearson T. A. Guillory J. D. Fabricant 《Colloid and polymer science》1999,277(6):557-562
We report synthesis and characterization of a macroporous polymeric material containing a covalently immobilized pore-surface
phase of well-defined thickness, gel-phase porosity and organic functional group content. The pore surfaces of otherwise inert
macroporous (32 μm mean pore size) ultrahigh-molecular-weight polyethylene (UHMWPE) are aminated throughout using a low-pressure
flowing-discharge process to enable covalent immobilization of lightly cross-linked polymer colloid particles on all pore
surfaces in the monolith. Solvent swelling and chemical derivitization of the covalently immobilized polymer colloid particles
produce a pore-surface gel phase of well-defined thickness, organic amine content, and gel-phase porosity. The low degree
of cross-linking in the polymer colloid particles prevents dissolution of the immobilized colloid in good solvents and enables
the formation of pore-surface gel phases having high gel porosity on swelling in good solvents. The pore-surface amination
introduced by the flowing discharge process varies by less than 17% through 5-mm thickness of the macroporous UHMWPE material.
The properties of the pore-surface gel phase also vary by less than 17% through the cross section. The pore-surface immobilized
polymer colloid particles swell by a factor of 10 in water and tetrahydrofuran after derivitization with polyethylene glycol.
Received: 20 November 1998 Accepted in revised form: 21 January 1999 相似文献
12.
A test of the quality of the electrostatic properties and polarizabilities used in the nonempirical molecular orbital (NEMO)
potential is carried out for formamide by calculating the molecular dipole moment and polarizability at the second-order M?ller–Plesset
(MP2) level of theory. The molecular dipole moment is 11% lower at the MP2 level than at the Hartree–Fock (HF) level, whereas
the isotropic part of the polarizability is increased by 36% by adding electron correlation and using a considerably larger
basis set. The atomic charges, dipole moments and polarizabilities obtained at the HF level are rescaled to get the correct
molecular properties at the MP2 level. The potential minimum for the cyclic dimer of formamide is −17.50 kcal/mol with the
MP2-scaled properties and is significantly lower than other potentials give. Two intermolecular potentials are constructed
and used in subsequent molecular dynamics simulations: one with the regular NEMO potential and the other with the rescaled
MP2 properties. A damping of the electrostatic field at short intermolecular distances is included in the present NEMO model.
The average energies for liquid formamide are lower for the MP2-scaled model and are in good agreement with experimental results.
The lowering of the simulation energy for the MP2-scaled potential indicates the strong dispersive interactions in liquid
formamide.
Received: 20 March 2000 / Accepted: 18 April 2000 / Published online: 18 August 2000 相似文献
13.
Sándor Kristyán Adrienn Ruzsinszky Gábor I. Csonka 《Theoretical chemistry accounts》2001,106(6):404-411
Experimental enthalpies of formation have been approximated using single-point Hartree–Fock (HF)–self-consistent-field (SCF)
total energies plus the rapid estimation of basis set error and correlation energy from partial charges (REBECEP) energy corrections.
The energy corrections are calculated from the HF–SCF partial atomic charges and optimized atomic energy parameters. The performance
of the method was tested on 51 closed-shell neutral molecules (50 molecules from the G3/99 thermochemistry database plus urea,
composed of H, C, N, O, and F atoms). The predictive force of the method is demonstrated, because these larger molecules were
not used for the optimization of the atomic parameters. We used the earlier RECEP-3 [HF/6-311+G(2d,p)] and REBECEP [HF/6-31G(d)]
atomic parameter sets obtained from the G2/97 thermochemistry database (containing small molecules) together with natural
population analysis and Mulliken partial charges. The best results were obtained using the natural population analysis charges,
although the Mulliken charges also provide useful results. The root-mean-square deviations from the experimental enthalpies
of formation for the selected 51 molecules are 1.15, 3.96, and 2.92 kcal/mol for Gaussian-3, B3LYP/6-11+G(3df,2p), and REBECEP
(natural population analysis) enthalpies of formation, respectively (the corresponding average absolute deviations are 0.94,
7.09, and 2.27 kcal/mol, respectively). The REBECEP method performs considerably better for the 51 test molecules with a moderate
6-31G(d) basis set than the B3LYP method with a large 6-311+G(3df,2p) basis set.
Received: 10 March 2001 / Accepted: 5 July 2001 / Published online: 11 October 2001 相似文献
14.
A simple and variationally stable quasi-relativistic method based on a modified low-order (LO) approximation to the normalized
elimination of the small component (NESC) method is presented. The modification of the original LO-NESC scheme implies the
use of an energy-independent factor in the relativistic correction to the potential energy. This factor cuts off the potential
energy at short distances from the nucleus and in this way restores the variational stability of LO-NESC. The new method,
dubbed LO-NESC-effective potential (EP) was tested in calculations on one-, two- and many-electron atoms. The LO-NESC-EP can
be easily implemented into the existing nonrelativistic quantum-chemical program codes because its Hamiltonian matrix can
be expressed entirely in terms of the integrals appearing in a nonrelativistic calculation.
Received: 1 April 2002 / Accepted: 23 June 2002 / Published online: 30 August 2002 相似文献
15.
H. Lee Woodcock Milan Hodošček Paul Sherwood Yong S. Lee Henry F. Schaefer III Bernard R. Brooks 《Theoretical chemistry accounts》2003,109(3):140-148
A replica path method has been developed and extended for use in complex systems involving hybrid quantum/classical (quantum
mechanical/molecular mechanical) coupled potentials. This method involves the definition of a reaction path via replication
of a set of macromolecular atoms. An “important” subset of these replicated atoms is restrained with a penalty function based
on weighted root-mean-square rotation/translation best-fit distances between adjacent (i±1) and next adjacent (i±2) pathway steps. An independent subset of the replicated atoms may be treated quantum mechanically using the computational
engine Gamess-UK. This treatment can be performed in a highly parallel manner in which many dozens of processors can be efficiently
employed. Computed forces may be projected onto a reference pathway and integrated to yield a potential of mean force (PMF).
This PMF, which does not suffer from large errors associated with calculated potential-energy differences, is extremely advantageous.
As an example, the QM/MM replica path method is applied to the study of the Claisen rearrangement of chorismate to prephenate
which is catalyzed by the Bacillus subtilis isolated, chorismate mutase. Results of the QM/MM pathway minimizations yielded an activation enthalpy ΔH
†† of 14.9 kcal/mol and a reaction enthalpy of −19.5 kcal/mol at the B3LYP/6-31G(d) level of theory. The resultant pathway was
compared and contrasted with one obtained using a forced transition approach based on a reaction coordinate constrained repeated
walk procedure (ΔH
†† =20.1 kcal/mol, ΔH
rxn = −20.1 kcal/mol, RHF/4-31G). The optimized replica path results compare favorably to the experimental activation enthalpy
of 12.7±0.4 kcal/mol.
Received: 16 December 2001 / Accepted: 6 September 2002 / Published online: 8 April 2003
Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 22nd National Meeting of the American Chemical
Society, 2001.
Correspondence to: H.L. Woodcock e-mail: hlwood@ccqc.uga.edu
Acknowledgements. The authors thank Eric Billings, Xiongwu Wu, and Stephen Bogusz for helpful discussions and related work. The authors also
show grateful appreciation to The National Institutes of Health and The National Science Foundation for support of the current
research. 相似文献
16.
Fabienne Alary Romuald Poteau Jean-Louis Heully Jean-Claude Barthelat Jean-Pierre Daudey 《Theoretical chemistry accounts》2000,104(3-4):174-178
A new method for an increased numerical efficiency of ab initio calculations is proposed. It is based on the assumption that
in most cases chemical properties of functional groups in molecules are mainly controlled by a few electrons. This statement
allows one to distinguish between two classes of nuclei and electrons: active and inactive ones. The effective group potential
(EGP) method presupposes that the effect of inactive electrons in a functional chemical group can be described by a pseudopotential,
in the same way that core electrons are replaced by effective core potentials in atoms. It is shown that EGPs are able to
predict chemical and structural features of the active part of a molecule and at a fraction of the ordinary computational
cost. The preliminary results reported here concern the determination of EGPs for ammonia, the methyl radical and the cyclopendadienyl
ligand, which represent different types of bonding.
Received: 15 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000 相似文献
17.
We have investigated the S0 and S1 electronic states in bacteriorhodopsin using a variety of QM/MM levels. The decomposition of the calculated excitation energies
into electronic and electrostatic components shows that the interaction of the chromophore with the protein electric field
increases the excitation energy, while polarization effects are negligible. Therefore, the experimentally observed reduction
in excitation energy from solution phase to protein environment (the Opsin shift) does not come from the electrostatic interaction
with the protein environment, but from either the interaction ofthe chromophore with the solvent or counter ion, or structural
effects. Our high-level ONIOM(TD– B3LYP:Amber) calculation predicts the excitation energy within 8 kcal/mol from experiment,
the discrepancy probably being caused by the neglect of polarization of the protein environment. In addition, we have shown
that the level of optimization is extremely critical for the calculation of accurate excitation energies in bacteriorhodopsin.
Received: 13 October 2001 / Accepted: 6 September 2002 / Published online: 3 February 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: K. Morokuma e-mail: morokuma@emory.edu 相似文献
18.
A variety of atomic and molecular properties can be expressed in terms of the electrostatic potential. These include energies,
covalent and anionic radii, electronegativities (chemical potentials) and a variety of properties that depend upon noncovalent
interactons. We present a survey of such relationships, which may be exact or approximate; they may involve the potential
in three-dimensional space, along the axes between bonded atoms, at nuclei or on molecular surfaces. Thus, the electrostatic
potential, which is rigorously related to the electronic density by Poisson's equation, can be regarded as, effectively, another
fundamental determinant of atomic and molecular properties.
Received: 6 March 2002 / Accepted: 15 May 2002 / Published online: 29 July 2002 相似文献
19.
In order to explore the isotope effect including the nuclear–electronic coupling and nuclear quantum effects under the one-particle
approximation, we apply the dynamic extended molecular orbital (DEMO) method and energy component analysis to the hydrogen
and lithium hydride isotope molecules. Since the DEMO method determines both electronic and nuclear wave functions simultaneously
by variationally optimizing all parameters embedded in the basis sets, the virial theorem is completely satisfied and guarantees
the relation of the kinetic and potential energies. We confirm the isotope effect on internuclear distances, nuclear and electronic
wave functions, dipole moment, the polarizability, and each energy component. In the case of isotopic species of the hydrogen
molecule, the total energy decreases from the H2 to the T2 molecule due to the stabilization of the nuclear–electronic potential component, as well as the nuclear kinetic one. In the
case of the lithium hydride molecule, the energy lowering by replacing 6Li with 7Li is calculated to be greater than that by replacing H with D. This is mainly caused by the small destabilization of electron–electron
and nuclear–nuclear repulsion in 7LiH compared to 6LiH, while the change in the repulsive components from 6LiH to 6LiD increases.
Received: 24 March 1999 / Accepted: 5 August 1999 / Published online: 15 December 1999 相似文献
20.
Ab initio calculations with inclusion of correlation effects at the MP2/6-31G* level have been used to predict the interaction
energy of stacked cytosine dimer (C/C) as a function of twisting and sliding in the gas phase. Systematic calculations have
also been carried out on the solvation free energies of various rotated and translated C/C dimers using a polarized continuum
model approach at the HF/6-31G* level with a view to probe the role of various degrees of freedom on the free energy of solvation
of the C/C dimer. The interaction energy of the C/C dimer decreases upon changing from a parallel to an antiparallel conformation
in the gas phase. The 180°-rotated conformation has been found to be the most stable arrangement when compared to other rotated
positions. The rotated and translated dimers exhibit lower solvation free energy than the parallel conformation. The decrease
in the dipole moment upon rotation from the parallel to the antiparallel conformation indicates the cancellation of charge
distribution upon rotation in the z direction of one cytosine base with respect to the other. The calculation reveals that the present approach could not yield
association energy, ΔΔG
Asso, in a solvent medium. This may be due to the fact that in the case of floppy molecules the contribution from translational,
rotational and vibrational free energies plays a significant role in the calculation of ΔΔG
Asso.
Received: 13 December 2001 / Accepted: 25 March 2002 / Published online: 13 June 2002 相似文献