摘要:

AbstractMulti‐ζ Slater‐type orbitals are frequently used in molecular orbital calculations. Master formulae and numerical tables are available in literature for overlap integrals betweens,p, anddatomic orbitals up to principal quantum number (n) = 3 and for some other selected quantum numbers. However, no master formula or numerical table is available for quantum numbersn= 5 and above and involving ƒ orbitals. In this article recursion formulae have been presented for the calculation of the overlap integral between any twos,p,d, and ƒ atomic orbitals formed by a linear combination of Slater‐type orbitals. These formulae, when expanded, would give rise to all the master formulae reported in the literature as well as formulae hitherto un

ISSN:0192-8651    

DOI:10.1002/jcc.540080102

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractComparison of the optimized geometries and SCF energies for the series XO 2+, XO2, XO 2−, XO 2−, with X = S,N shows thatd(S) functions cause larger bond shortening and energy drop thandfunctions centered on first‐row atoms. This is further emphasized on comparing the separate effects ofd(central atom) andd(O) functions for SO2and NO 2−, which are similar only for the first‐row molecule. Thed(S) functions are also essential for proper prediction of the OSO angles. The deformation densities calculated for each series and the corresponding X–O shared populations, change as expected on adding electrons first into σ* then into π* molecular orbitals. In the regions around nuclei the deformation densities express the behavior of the atomicsandpvalence orbitals or of their product inside their radial nodes. Introduction ofdfunctions causes substantial polarization effects. For X = N these are mostly local except in the bonding regions whered(N) andd(O) functions are somewhat interchangeable. However,d(S) functions induce also unique changes in the deformation density near O. They cause π and π′ charge migration from O to S and a σ flow in the opposite direction. These effects are largest for the hypervalent species. The unique populations of thed(S) functions are much larger than those ofd(N) andd(O) functions. The contribution ofd(S) functions to bonding is related to the larger amplitude at small radii of the atomic 3d(S) orbital as compared with that of 3d(N). The difference in amplitudes is related to penetration effects. Diffusepfunctions affect geometries and SCF energies of doubly, but not singly negative ions. However, they mostly describe the diffuse nonbonding clouds and do n

ISSN:0192-8651    

DOI:10.1002/jcc.540080103

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractPolymer conformational analyses can require being able to model the intramolecular energetics of a very long (infinite) chain employing calculations carried out on a relatively short chain sequence. A method to meet this need, based upon symmetry considerations and molecular mechanics energetics, has been developed. GivenNequivalent degrees of freedom in a linear polymer chain,Nunique molecular groups are determined within the chain. A molecular unit is defined as a group of atoms containing backbone rotational degrees of conformational freedom on each of its ends. The interaction of theseNmolecular groups, each with a finite number of nearest neighbors, properly describe the intramolecular energetics of a long (infinite) polymer chain. Thus, conformational energetics arising from arbitrarily distant neighbor interactions can be included in the estimation of statistical and thermodynamic properties of a linear polymeric system. This approach is called the polymer reduced interaction matrix method (PRIMM) and the results of applying it to isotactic polystyrene (I‐PS) are presented by way of exampl

ISSN:0192-8651    

DOI:10.1002/jcc.540080104

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe evolution of the CIPSI method, with the latest modifications recently implemented in our laboratory, is described. A new version, based on a diagrammatic technique, is presented. Test calculations which have been run on water, ethylene, and transacrolein, show that the new method is a powerful tool for the study of medium‐size molecular system

ISSN:0192-8651    

DOI:10.1002/jcc.540080105

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractEnergies obtained by configuration interaction calculations including all double excitations with regard to the Hartree‐Fock reference determinant can empirically be corrected to size consistency using either the Langhoff‐Davidson (LD) formula or a formula suggested by Pople, Seeger, and Krishnan (PSK). Semiempirical MNDOC calculations suggest that for molecular systems with a large number of electrons and important correlation effects the PSK correction is superior to the LD correct

ISSN:0192-8651    

DOI:10.1002/jcc.540080106

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe potential energy surface of the van der Waals system HeLi2 is computed for the case in which the system hasC2vsymmetry and at the Li‐Li distance (5.005 bohrs). A comparative study of the results for the two methods used,ab initioHartree‐Fock and second‐order Møller‐Plesset, and several basis sets, ranging from minimal to near Hartree‐Fock quality, is also done. The results show the importance of correcting the basis set superposition error, and the need, in order to obtain a good description of the potential, of basis sets with polarization functions on all the atoms, when the Møller‐Plesset method is used. At the Hartree‐Fock level, the MINI‐1 basis gives results almost of the same quality as the near H

ISSN:0192-8651    

DOI:10.1002/jcc.540080107

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractUsing previously reportedab initiopotentials of the intermolecular interaction energies of phospholipid (PL), Lysophosphatidyl Ethanolamine, with one Na+ion and one water molecule, we performed Monte Carlo simulations for PL‐water and PL‐Na+‐water systems. Water‐water and PL‐water interaction energetics of PL hydration sites are analyzed to understand, in a qualitative way, why the PL head part shows hydrophilicity and the tail part shows hydrophobicity. The interaction of Na+with PL, as well as the interaction of water with PL, is visualized from the analysis of the hydration structures near PL, and the radial distribution functions are analyzed for selected hydration sites. The PL molecule shows much stronger interaction with Na+than with water. The Na+ion is likely to be strongly bound to PO 4−, even to the extent of being trapped, whereas, for water, there exist two strong binding regions near NH 3+and PO 4−. Three water molecules near NH 3+are much more strongly bound than four water molecules near the double‐bonded oxygens of PO 4−. The hydrogens of CH2adjacent to NH 3+show somewhat strong hydrophilicity, while the hydrogens of CH2adjacent to PO 4−does not show such characteristics. The CH2groups at the PL tail part give repulsive interactions with water molecules, showing hydrophobicity. Water molecules near the PL tail are stabilized

ISSN:0192-8651    

DOI:10.1002/jcc.540080108

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIntermolecular potential functions have been used to determine the equilibrium structures of the water‐pyridine complexes. The dimer and symmetrical 2:1 water pyridine systems have been studied. Three water models, ST2, TIPS2, and EMPWI have been combined with two different Lennard Jones nonbonded parameters and various charge distributions for the pyridine molecule to describe the systems. For the dimer, results show two distinguishable classes of preferential hydration sites, which are specific sites corresponding to hydrogen‐bonded dimer and nonspecific sites located near the hydrophobic regions. Calculations performed on hydrogen‐bonded symmetrical complexes show that the planar complex is generally less stable than the complex with water molecules perpendicular to the pyridine plane. For these complexes, the major factor that influences the hydrogen‐bonded configurations is the choice of the water model. The importance of atomic charge distributions for the solute over the choice of potential parameters is pointed out. Finally, the effective lone pair representation on the aromatic nitrogen atom is shown to improve the hydrogen bond geometry and the stability of the co

ISSN:0192-8651    

DOI:10.1002/jcc.540080109

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractBasis set superposition error in hydrogen‐bonded systems can exaggerate attraction calculated from self‐consistent field energies as well as from electron correlation energies. One cause of this error is the basis set deficiency in describing the charge polarization of one constituent molecule when its bonding partner approaches. That constituent molecule's description is improved partly because of the proximity of the partner's basis functions, independent of real attraction. That polarization‐related error is shown to occur primarily at the SCF level and not at correlated l

ISSN:0192-8651    

DOI:10.1002/jcc.540080110

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe effect of polarization functions forab initiomolecular orbital calculations at the 3‐21G* level has been studied for disiloxane. Calculated molecular geometry, dipole moment, and the linearization barrier variation were analyzed for different uncontracted polarization functions. It was concluded that variation of the polarization function on oxygen has only a minor influence on the molecular properties of disiloxane, but its presence is required to obtain a bent geometry for the disiloxane bond. The calculated molecular properties of disiloxane are greatly influenced when the polarization function on silicon is varied. Two different values (0.3 and 0.9) for the exponent of the silicon polarization function provide results comparable to the experimental values for disiloxane. The only significant differences between the results obtained fromab initiocalculations using the two polarization functions are in net atomic charges. The uncontracted polarization function of silicon with a value of 0.3 for its exponent is transferable to other organosilicon compounds. Calculated molecular geometries of flexible or rigid structures are in very good agreement with the experimental value

ISSN:0192-8651    

DOI:10.1002/jcc.540080111

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY