Representations of the symmetric group generated by projected spin functions: A graphical approach

The representation matrices generated by the projected spin functions have some very interesting properties. All the matrix elements are integers and they are quite sparse. A very efficient algorithm is presented for the calculation of these representation matrices based on a graphical approach and a new indexing scheme for representation of primitive spin functions is introduced. Test calculations show that the method is very fast and suited for calculations on vector computers. © 1996 John Wiley & Sons, Inc.     

A new algorithm to handle finite nuclear mass effects in electronic calculations: the ISOTOPE program

We report the development of a simple algorithm to modify quantum chemistry codes based on the LCAO procedure, to account for the isotope problem in electronic structure calculations. No extra computations are required compared to standard Born-Oppenheimer calculations. An upgrade of the Gamess package called ISOTOPE is presented, and its applicability is demonstrated in some examples.     

On the validity and applicability of the connected moments expansion

The theoretical justification, and typical convergence properties, of Cioslowski's connected moments expansion for the ground-state energy of a quantum-mechanical system are considered. This size extensive expansion is an alternative to Rayleigh-Schrodinger perturbation theory, and is expected to be useful in electronic structure calculations based on many-determinant reference functions, where perturbation theory is not applicable. It is found from example molecular electronic structure calculations that, in some cases, the expansion does not converge correctly to the true energy. An im- proved expansion derived from a padé approximant, and an analysis of its validity, is presented here.     

Molecular orbital analysis of the bondig in platinum phosphine hydride clusters

The electronic and structural features of platinum clusters containing tertiary phosphine and hydride ligands have been analysed using Extended Hückel molecular orbital calculations. The calculations illustrate how the non-conical nature of the constituent PtL₂ fragments leads to their having a marked conformational preference in the clusters. The introduction of PtL fragments into some of the clusters leads to a further flexibility in electron count which may also be rationalised on the basis of the analysis presented here.     

The Hylleraas-CI method in molecular calculations. III. Implementation and numerical verification of a three-electron many-center theory

The general theory of three-electron Hylleraas-Configuration-Interaction method using linear correlation factors of the form r_ij has been implemented for molecular systems using cartesian Gaussians as basis sets. A brief review of the theory and the form of the three-electron integrals is presented. Additionally, a table of numerical values of some selected three-electron integrals is given. Results from test calculations on H₃ using the full form of the theory are presented for some simple basis sets. A discussion of the computational problems that need to be overcome before this approach is competitive with traditional methods is included.     

单一组分分子基导体的研究进展

概述了单组分分子性金属的设计和实现过程,并对一些典型的单组分分子导体体系的结构和物理性质作了简单介绍.     

Computational electrochemistry: aqueous two-electron reduction potentials for substituted quinones

The electrode potentials of some quinone derivatives in aqueous solution have been calculated. The calculations are carried out at the Hartree–Fock and B3LYP levels with the inclusion of entropic and thermochemical corrections to yield free energies of redox reactions. The Polarisable Continuum Model (PCM) is used to describe the solvent. The average error of calculation of electrode potentials is less than 0.03 V and is decreased compared to the average error of methods presented previously. The role of relaxation energies and frequency calculations in improving the results has been investigated.     

Fully relativistic correlated benchmark results for uranyl and a critical look at relativistic effective core potentials for uranium

 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     

Numerical integration of the Kohn–Sham equations: Integral method for bound states

A numerical method is presented that solves the multicenter Kohn–Sham equations. The method couples the resolution of the integral form of the equation at a given energy with an iterative search for the eigenvalues. The validity of the method is checked by comparing some test calculations for diatomics with results in the literature from other numerical methods. For these calculations the wave functions are expanded in partial waves either on one center or on two centers with the help of the partitioning of space in fuzzy cells. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 74: 49–54, 1999     

The intermolecular interactions in binaries

The recapitulation of systematical investigations of excess enthalpy of mixing in binary mixtures: pyridine base +n-alkane or some of arenes is presented. On the base of experimental results as well as model calculations (PFP, ERAS) the discussion of intermolecular interactions in pyridine bases is given.     

Calculation of the electronic structure of formaldehyde using overlapping spheres in the SCF Xα scattered-wave method

It has recently been established that physical realism of the results can be improved within the framework of the self-consistent statistical exchange multiple scattering wave method if the atomic spheres are allowed to overlap. Here we report that by semi-empirically adjusting the overlap of the atomic spheres, the ionization potentials and total energy are in better agreement with experiment, and the order of levels A₁ and B₂ in formaldehyde is reversed with respect to some other calculations. The electronic energy level structure calculated here is in agreement with the experimental results. A systematic study of the overlapping scheme for formaldehyde is presented and the results are compared with experiments and other theoretical calculations.     

Accurate quantum-chemical calculations using Gaussian-type geminal and Gaussian-type orbital basis sets: applications to atoms and diatomics

We have implemented the use of mixed basis sets of Gaussian one- and two-electron (geminal) functions for the calculation of second-order M?ller-Plesset (MP2) correlation energies. In this paper, we describe some aspects of this implementation, including different forms chosen for the pair functions. Computational results are presented for some closed-shell atoms and diatomics. Our calculations indicate that the method presented is capable of yielding highly accurate second-order correlation energies with rather modest Gaussian orbital basis sets, providing an alternative route to highly accurate wave functions. For the neon atom, the hydrogen molecule, and the hydrogen fluoride molecule, our calculations yield the most accurate MP2 energies published so far. A critical comparison is made with established MP2-R12 methods, revealing an erratic behaviour of some of these methods, even in large basis sets.     

On the proton affinity of pteridine

All-valence-electron and perturbation calculations suggest that pteridine may preferably be protonated at the pyrazine moiety. Correlation between these results and some experimental data is presented.     

Transferred hyperfine structure interactions in transition metal complexes

The transferred hyperfine interactions of octahedral transition metal complexes are discussed. The necessity of using a model which accounts for spin polarization is stressed. Results obtained by molecular orbital calculations using the multiple scattering method are presented for thirteen different octahedral clusters. The agreement with experiments is satisfactory except for the contact term where it is only moderately good. Even in the latter case, however, the calculations yield some valuable information, particularly concerning the core polarization contribution.     

The DFT investigations of the electron injection in hydrazone-based sensitizers

A brief review of popular polarizable potentials for water, including both those parameterized to fit experimental properties, typically of the liquid, or electronic structure calculations on small clusters, is presented. The recently developed POLIR potential, which was parameterized to reproduce both ab initio calculations on clusters and the experimental liquid IR spectrum, is discussed, and some new results for both clusters and the liquid phase are shown, indicating its transferable nature.     

Some recent developments in the quantum theory of hydrogen bonding and other effects in proteins

Standard ab initio quantum chemical computations are quite effective in throwing light on binding features of biomolecules, in particular, hydrogen bonds. This is illustrated by a brief survey of recent work, including some interesting preliminary results on dipeptides, tripeptides, and tetrapeptides. Differential-energy maps for analyzing results are presented and discussed. Basic theoretical questions, such as the significance of minimal-basis calculations and localization on a subsection of a macromolecule, are also discussed.     

Can MM‐PBSA calculations predict the specificities of protein kinase inhibitors?

An application of the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) protocol to the prediction of protein kinase inhibitor selectivity is presented. Six different inhibitors are placed in equivalent orientations in each of six different receptors. Fully solvated molecular dynamics is then run for 1 ns on each of the 36 complexes, and the resulting trajectories scored, using the implicit solvent model. The results show some correlation with experimentally-determined specificities; anomalies may be attributed to a variety of causes, including difficulties in quantifying induced fit penalties and variabilities in normal modes calculations. Decomposing interaction energies on a per-residue basis yields more useful insights into the natures of the binding modes and suggests that the real value of such calculations lies in understanding interactions rather than outright prediction.     

A 15N NMR investigation of some azolopyridines

¹⁵N NMR chemical shift data are presented for 14 azolopyridines, together with the results of INDO/S-SOS calculations of nitrogen shieldings. Previous ¹⁴N NMR results for some of these compounds are reinterpreted. The ¹⁴N data and their assignments are shown to be reliable for the indolizine nitrogen atom from arguments based on relative line widths. The pyridine-type nitrogens are more reliably assigned from the ¹⁵N spectra combined with the results of the INDO/S-SOS calculations for individual molecules. A combination of ¹⁴N and ¹⁵N NMR spectra, together with the shielding calculations, provides a basis for unambiguous assignments of all the various nitrogen environments considered.     

Many-Electron,multicenter integrals in superposition of correlated configurations method. I. one- and two-electron integrals

The calculations by means of the superposition of correlated configurations method (Hylleraas-CI ), that is, the combination of configuration interaction with the Hylleraas-type correlation factors, needs the effective evaluation of some nontrivial integrals. This series of papers gives the formulas for all types of integrals needed for molecular calculations when Gaussian lobe functions are used as a basis set. The formulas for two-electron integrals are given in the present paper. The preliminary results for two-electron systems are presented.     

Improving numerical integration through basis set expansion

Calculations are presented to assess a theorem presented by S.F. Boys [(1969) Proc. R. Soc. A. 309:195], regarding the accuracy of numerical integration in quantum chemical calculations. The theorem states that the error due to numerical integration can be made proportional to the error due to basis set truncation, and thus goes to zero in the limit of a complete basis. We test this theorem on the hydrogen atom, showing that with a solution-spanning basis, the numerically exact orbital energy can indeed be calculated with a small number of integration points. Moreover, tests for H and H₂⁺ demonstrate that even when only a near-complete basis is employed, Boys Theorem can significantly reduce integration error. However, for other systems, like the oxygen atom and the CO₂ molecule, the theorem yields no advantage for some occupied orbitals. It is concluded that the theorem would be most useful for calculations that demand large basis sets.