NaX型沸石分子筛中吸附质分子结构与吸附热的关系

近年来,沸石分子筛结构与性能关系的理论计算研究工作愈来愈受到人们的重视[‘－0．人工合成的N     

Explicitly correlated local second-order perturbation theory with a frozen geminal correlation factor

The recently introduced MP2-R122*A(loc) and LMP2-R122*A(loc) methods are modified to use a short-range correlation factor expanded as a fixed linear combination of Gaussian geminals. Density fitting is used to reduce the effort for integral evaluation, and local approximations are introduced to improve the scaling of the computational resources with molecular size. The MP2-F122*A(loc) correlation energies converge very rapidly with respect to the atomic orbital basis set size. Already with the aug-cc-pVTZ basis the correlation energies computed for a set of 21 small molecules are found to be within 0.5% of the MP2 basis set limit. Furthermore the short-range correlation factor leads to an improved convergence of the resolution of the identity, and eliminates problems with long-range errors in density fitting caused by the linear r12 factor. The DF-LMP2-F122*A(loc) method is applied to compute second-order correlation energies for molecules with up to 49 atoms and more than 1600 basis functions.     

A natural linear scaling coupled-cluster method

It is shown that using an appropriate localized molecular orbital (LMO) basis, one is able to calculate coupled-cluster singles and doubles (CCSD) wave functions and energies for very large systems by performing full CCSD calculations on small subunits only. This leads to a natural linear scaling coupled-cluster method (NLSCC), in which total correlation energies of extended systems are evaluated as the sum of correlation energy contributions from individual small subunits within that system. This is achieved by defining local occupied orbital correlation energies. These are quantities, which in the LMO basis become transferable between similar molecular fragments. Conventional small scale existing molecular CCSD codes are all that is needed, the local correlation effect being simply transmitted via the appropriate LMO basis. Linear scaling of electronic correlation energy calculations is thus naturally achieved using the NLSCC approach, which in principle can treat nonperiodic extended systems of infinite basis set size. Results are shown for alkanes and several polyglycine molecules and the latter compared to recent results obtained via an explicit large scale LCCSD calculation. (c) 2004 American Institute of Physics.     

Long‐range corrected functionals satisfy Koopmans' theorem: Calculation of correlation and relaxation energies

In this article, we show that the long‐range‐corrected (LC) density functionals LC‐BOP and LCgau‐BOP reproduce frontier orbital energies and highest‐occupied molecular orbital (HOMO)—lowest‐unoccupied molecular orbital (LUMO) gaps better than other density functionals. The negative of HOMO and LUMO energies are compared with the vertical ionization potentials (IPs) and electron affinities, respectively, using CCSD(T)/6‐311++G(3df,3pd) for 113 molecules, and we found LC functionals to satisfy Koopmans' theorem. We also report that the frontier orbital energies and the HOMO‐LUMO gaps of LC‐BOP and LCgau‐BOP are better than those of recently proposed ωM05‐D (Lin et al., J. Chem. Phys. 2012, 136 , 154109). We express the exact IP in terms of orbital relaxation, and correlation energies and hence calculate the relaxation and correlation energies for the same set of molecules. It is found that the LC functionals, in general, includes more relaxation effect than Hartree–Fock and more correlation effect than the other density functionals without LC scheme. Finally, we scan μ parameter in LC scheme from 0.1 to 0.6 bohr^?1 for the above test set molecules with LC‐BOP functional and found our parameter value, 0.47 bohr^?1, is usefully applicable to our tested systems. © 2013 Wiley Periodicals, Inc.     

Soft Coulomb hole method applied to molecules

The soft Coulomb hole method introduces a perturbation operator, defined by ?e/r₁₂ to take into account electron correlation effects, where ω represents the width of the Coulomb hole. A new parametrization for the soft Coulomb hole operator is presented with the purpose of obtaining better molecular geometries than those resulting from Hartree–Fock calculations, as well as correlation energies. The 12 parameters included in ω were determined for a reference set of 12 molecules and applied to a large set of molecules (38 homo‐ and heteronuclear diatomic molecules, and 37 small and medium‐size molecules). For these systems, the optimized geometries were compared with experimental values; correlation energies were compared with results of the MP2, B3LYP, and Gaussian 3 approach. On average, molecular geometries are better than the Hartree–Fock values, and correlation energies yield results halfway between MP2 and B3LYP. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

ESCAPE: A novel approach for a fast estimation of dynamic correlation energies: Application to large organic molecules

Advanced wave function-based quantum chemical ab initio methods, such as CCSD(T), are able to calculate the energies of small- to medium-sized molecules with chemical accuracy. Unfortunately, these methods scale quite unfavorably with the size of the system and are getting too time consuming—and too expensive—for larger molecules. In order to be able to treat larger organic molecules, we propose a novel scheme for a quick and reliable estimate of molecular correlation energies, which we call ESCAPE (ES timation of C orrelA tion energies by P air E nergies). It is based on the pair correlation energies for localized molecular orbitals that have been generated by CCSD[T] and fitted to suitable functional forms. All fit parameters are stored in a large parameter file. Aiming at chemical accuracy (±1 kcal/mol), we have first limited our approach to aliphatic hydrocarbons. The total molecular CCSD[T] correlation energies of a training set of 41 aliphatic hydrocarbons could be reproduced with a mean absolute error (MAE) of 0.56 kcal/mol or 0.11%. A similar accuracy could be obtained for a test set of 11 additional hydrocarbons with up to eight carbon atoms (MAE of 0.65 kcal/mol or 0.09%). In a more critical test, we checked the small energy differences for a set of 13 isomerization reactions. The comparison with experimental data showed that we could reach chemical accuracy as well. Our estimate (MAE of 0.55 kcal/mol) is slightly inferior to the CCSD[T] result (MAE of 0.17 kcal/mol), but superior to SCF, DFT/B3LYP, and DFT/B3LYP + D3. Moreover, in all cases, we obtained the correct sign, that is, the correct equilibrium structure. A similar accuracy could be reached in an application to the three lowest isomers of the C₆₀ molecule. Using the example of a set of eight alcohols, we were able to proof the method's ability for molecules including heteroatoms. Three fast steps are necessary for the application to any aliphatic hydrocarbon or alcohol: (1) An SCF calculation at the selected molecular geometry; it can be fast since a medium size basis set is generally sufficient. (2) The localization of the occupied molecular orbitals and determination of their properties (center of charge and spatial extent). (3) Estimate of the correlation energy using the existing parameter file. © 2019 Wiley Periodicals, Inc.     

Hydration energies of Thallium(I) halides—a novel simulation methodology

A simple simulation methodology to estimate the hydration energies and surface potentials of thallium halides is proposed, incorporating random distribution of molecules, nearest neighbor distances and hydration numbers. The extent of dehydration during each step and the corresponding variation in the hydration numbers are evaluated, assuming the validity of hard spheres. The correlation of the computed hydration energies with molecular sizes, lattice energies, crystal structures and feasibility of complexation reactions is discussed.     

Correlation energy extrapolation by intrinsic scaling. IV. Accurate binding energies of the homonuclear diatomic molecules carbon, nitrogen, oxygen, and fluorine

The method of extrapolation by intrinsic scaling, recently introduced to obtain correlation energies, is generalized to multiconfigurational reference functions and used to calculate the binding energies of the diatomic molecules C2, N2, O2, and F2. First, accurate approximations to the full configuration interaction energies of the individual molecules and their constituent atoms are determined, employing Dunning's correlation consistent double-, triple- and quadruple zeta basis sets. Then, these energies are extrapolated to their full basis set limits. Chemical accuracy is attained for the binding energies of all molecules.     

Free energy of solvation from molecular dynamics simulation applying Voronoi-Delaunay triangulation to the cavity creation

The free energy of solvation for a large number of representative solutes in various solvents has been calculated from the polarizable continuum model coupled to molecular dynamics computer simulation. A new algorithm based on the Voronoi-Delaunay triangulation of atom-atom contact points between the solute and the solvent molecules is presented for the estimation of the solvent-accessible surface surrounding the solute. The volume of the inscribed cavity is used to rescale the cavitational contribution to the solvation free energy for each atom of the solute atom within scaled particle theory. The computation of the electrostatic free energy of solvation is performed using the Voronoi-Delaunay surface around the solute as the boundary for the polarizable continuum model. Additional short-range contributions to the solvation free energy are included directly from the solute-solvent force field for the van der Waals-type interactions. Calculated solvation free energies for neutral molecules dissolved in benzene, water, CCl4, and octanol are compared with experimental data. We found an excellent correlation between the experimental and computed free energies of solvation for all the solvents. In addition, the employed algorithm for the cavity creation by Voronoi-Delaunay triangulation is compared with the GEPOL algorithm and is shown to predict more accurate free energies of solvation, especially in solvents composed by molecules with nonspherical molecular shapes.     

A refined cluster-in-molecule local correlation approach for predicting the relative energies of large systems

A refined cluster-in-molecule (CIM) method for local correlation calculations of large molecules is presented. In the present work, two new strategies are introduced to further improve the CIM approach: (1) Some medium-range electron correlation energies, which are neglected in the previous CIM approach, are taken into account. (2) A much simpler procedure using only a distance threshold is used to construct various clusters. To cover the medium-range correlation effect as much as possible, some two-atom-centered clusters are built, in addition to one-atom-centered clusters. Our test calculations at the second order perturbation theory (MP2) level show that the refined CIM method can recover about 99.9% of the conventional MP2 correlation energy using an appropriate distance threshold. The accuracy of the present CIM method is capable of providing reliable relative energies of medium-sized systems such as polyalanines with 10 residues, and water molecules with 50 water molecules. For polyalanines with up to 30 residues, we have demonstrated that the computational cost of the CIM-MP2 calculation increases linearly with the molecular size, but the required memory and disc-space do not need to increase for large systems. The improved CIM method has been used to compute the relative energy of ice-like (H(2)O)(96) clusters (with 2400 basis functions) and to predict the dimerization energy of a double-helical foldamer (with 2330 basis functions). The present CIM method is expected to be a practical local correlation method for describing the relative energies of large systems.     

Quantum-chemical investigation of the structures and electronic spectra of the nucleic acid bases at the coupled cluster CC2 level

We study the ground-state structures and singlet- and triplet-excited states of the nucleic acid bases by applying the coupled cluster model CC2 in combination with a resolution-of-the-identity approximation for electron interaction integrals. Both basis set effects and the influence of dynamic electron correlation on the molecular structures are elucidated; the latter by comparing CC2 with Hartree-Fock and M?ller-Plesset perturbation theory to second order. Furthermore, we investigate basis set and electron correlation effects on the vertical excitation energies and compare our highest-level results with experiment and other theoretical approaches. It is shown that small basis sets are insufficient for obtaining accurate results for excited states of these molecules and that the CC2 approach to dynamic electron correlation is a reliable and efficient tool for electronic structure calculations on medium-sized molecules.     

Shannon information entropy of fractional occupation probability as an electron correlation measure in atoms and molecules

A new method to determine electron correlation energy is presented for atoms and molecules. This method is based on Shannon information entropy that is obtained by fractional occupation probabilities of natural atomic orbitals. It is indicated that the Shannon entropy increases as the number of electrons increases and thus can be considered as a possible measure for the electron correlation in atomic and molecular systems. For neutral atoms and singly charged positive ions we proposed an expression for correlation energy with explicit dependence on the Shannon entropy and atomic number. The obtained correlation energies have been used to compute the first ionization potentials of the ground state of the main group elements from hydrogen through krypton. The calculated ionization potentials are in reasonably good agreement with their corresponding experimental values.We also developed the additivity scheme to find a connection between Shannon entropy and molecular correlation energy. The estimated molecular correlation energies show an excellent agreement with those obtained by elaborate G3 method with R² = 0.990.     

Hartree-Fock soft Coulomb hole to estimate correlation energies in atoms, molecules and polymers

We have shown that the empirical correction introduced into the Hartree-Fock method to calculate correlation energies for atoms and therefore to remove the error caused by the so-called Coulomb hole can be extended from atoms to molecules and polymers. A reformulation was required of the necessary parameter representation. The reparametrization has been performed staying as close as possible to the original expressions for atoms reported by Chakravorty and Clementi (S.J. Chakravorty and E. Clementi, Phys. Rev. A, 39 (1989) 2290). In addition to their work, where the correlation energy has been calculated with the self-consistent Hartree-Fock wavefunction and the correction integrals, we have performed investigations, including the perturbation operator in the Fock operator, so that the total energy also contains the correlation energy. The applications of this approach to atoms and molecules show that the total electron correlation energies and ionization potentials calculated as differences of total energies can be obtained very satisfactorily. On the basis of the reported calculations it turns out that one obtains better agreement with reference values of more sophisticated calculations when the correction integrals are used to build up the Fock matrix. Furthermore we have found that the magnitude of the correlation energy depends only weakly on the size of the basis sets, which makes this empirical method very attractive for its application to large molecular and polymeric systems.     

Fitting atomic correlation parameters for RECEP (rapid estimation of correlation energy from partial charges) method to estimate molecular correlation energies within chemical accuracy

The accuracy of the RECEP method [Chem Phys 1997, 224, 33 and Chem Phys Lett 1999, 307, 469] has been increased considerably by the use of fitted atomic correlation parameters. This method allows an extremely rapid, practically prompt calculation of the correlation energy of molecules after an HF‐SCF calculation. The G2 level correlation energy and HF‐SCF charge distribution of 41 closed‐shell neutral molecules (composed of H, C, N, O, and F atoms) of the G2 thermochemistry database were used to obtain the fitted RECEP atomic correlation parameters. Four different mathematical definitions of partial charges, as a multiple choice, were used to calculate the molecular correlation energies. The best results were obtained using the natural population analysis, although the other three are also recommended for use. For the 41 molecules, the G2 results were approached within a 1.8 kcal/mol standard deviation (the mean absolute difference was 1.5 kcal/mol). The RECEP atomic correlation parameters were also tested on a different, nonoverlapping set of other 24 molecules from the G2 thermochemistry database. The G2 results of these 24 molecules were approached within a 2.3 kcal/mol standard deviation (the mean absolute difference was 1.9 kcal/mol). This method is recommended to estimate total correlation energies of closed shell ground‐state neutral molecules at stationary (minimums and transition states) points on the potential surface. Extension of the work for charged molecules, radicals, and molecules containing other atoms is straightforward. Numerical example as a recipe is also provided. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 241–254, 2001     

Divide-and-conquer local correlation approach to the correlation energy of large molecules

A divide-and-conquer local correlation approach for correlation energy calculations on large molecules is proposed for any post-Hartree-Fock correlation method. The main idea of this approach is to decompose a large system into various fragments capped by their local environments. The total correlation energy of the whole system can be approximately obtained as the summation of correlation energies from all capped fragments, from which correlation energies from all adjacent caps are removed. This approach computationally achieves linear scaling even for medium-sized systems. Our test calculations for a wide range of molecules using the 6-31G or 6-31G( * *) basis set demonstrate that this simple approach recovers more than 99.0% of the conventional second-order Moller-Plesset perturbation theory and coupled cluster with single and double excitations correlation energies.     

Mechanism of negative ion formation from phenol and para-chlorophenol by interaction with free electrons

Dissociative electron attachment (DEA) to phenol and para-chlorophenol in the energy range 0-12 eV is studied. Analogies in formation of the resonance states in an ionic benzene and its derivatives are found to arise from the similarity of the aromatic base of the molecules. Differences in DEA processes are defined mainly by the influence of the functional OH-group and, to a lesser degree, by the presence of a chlorine atom. A correlation between the energies of the resonance states and ionization energies of p-chlorophenol and phenol, analogous to that found previously for phenol, is proved. On this basis it is established that the dominating mechanism for formation of molecular negative ions at energies above 5 eV is Feshbach resonance.Copyright 2000 John Wiley & Sons, Ltd.     

Scaling dynamical correlation energy from density functional theory correlation functionals

The scaling of dynamical correlation energy in molecules obtained by the correlation functionals of density functional theory (DFT) is examined. The approach taken is very similar to the scaled external correlation method of Brown and Truhlar but is based on the observation that DFT correlation functionals, especially the LYP, appear to represent the dynamical portion of the correlation energy in molecules. We examine whether higher accuracy in atomization energies can be gained by scaling without significant deterioration of the structural and spectroscopic properties of the molecules using four DFT functionals (BLYP, OLYP, B3LYP, and O3LYP) on 19 molecules including the six molecule AE6 database, the latter being representative of a much larger, 109 molecule training set. We show that, with molecule specific scale factors, nearly perfect agreement with experiment can be achieved in atomization energies without increasing the average errors in other molecular properties relative to the DFT calculation. We further show that it is possible to find optimal scale factors which reduce the mean unsigned error per bond to levels comparable to those of some multilevel multicoefficient methods.     

Transferability of Electronic Interaction Energies Between Localized Orbitals

Localized molecular orbitals have been shown to be transferable among structurally-related molecules. We further show that the electronic energies between localized orbitals are transferable and their magnitude can be estimated. A set of parameters of group interaction energies are established from the analysis of small molecules. Use of these parameters is demonstrated successfully for large molecules.     

Relationship of correlation energy and size

Analysis of available data on atoms has led to a relatively simple empirical relationship between the correlation energy and second moment <r²>, a measure of the size of the electron density. With the aid of this simple relationship it is possible to predict correlation energies with fair accuracy given the SCF or Hartree–Fock limit values for the size of the electron density. Preliminary extensions of this work to two- and ten-electron molecules indicate that it may be possible to predict molecular correlation energies to semiquantitative accuracy from SCF data on the electronic distribution.