Egan, J T MacElroy, R D
Published in
Journal of computational chemistry

A simple computational scheme for estimating the electrostatic potential about molecular models of moderate size is given. The large amount of calculations required for the evaluation of the hypersurface lends itself to treatment by high speed, unconventional computing machines. The essence of these calculations lies in Coulombic interactions that ...

DeFrees, D J McLean, A D
Published in
Journal of computational chemistry

The proton affinity of a molecule in the gas phase is a fundamental measure of its basicity and is the factor controlling the course of many ion-molecule reactions. In this article, ab initio molecular orbital theory at the MP4/6-311 ++ G(3df, 3pd) level of theory is demonstrated to predict proton affinities (PA's) for small neutral and anionic bas...

Sokalski, W A Shibata, M Ornstein, R L Rein, R
Published in
Journal of computational chemistry

The quality of several atomic charge models based on different definitions has been analyzed using cumulative atomic multipole moments (CAMM). This formalism can generate higher atomic moments starting from any atomic charges, while preserving the corresponding molecular moments. The atomic charge contribution to the higher molecular moments, as we...

Sokalski, W A Keller, D A Ornstein, R L Rein, R
Published in
Journal of computational chemistry

The defects in atomic monopole models of molecular charge distribution have been analyzed for several model-blocked peptides and compared with accurate quantum chemical values. The results indicate that the angular characteristics of the molecular electrostatic potential around functional groups capable of forming hydrogen bonds can be considerably...

Cioslowski, J Stefanov, B B Constans, P
Published in
Journal of computational chemistry

A new algorithm for quantitative assessment of similarity between two atoms in molecules is presented. Both the atomic similarity index and its derivatives with respect to the three Euler angles that describe the mutual orientation of the atoms under comparison are computed efficiently by taking advantage of the recently developed analytical repres...

Llano, J Montero, L A
Published in
Journal of computational chemistry

Extensive semiempirical SCF-MO calculations confirm that the exo-anomeric effect in methyl O-, N- and S-glycosides deals with an interaction of π-character along the C1 (SINGLE BOND)Y1 bond in a X5 (SINGLE BOND)C1 (SINGLE BOND)Y1 (SINGLE BOND)Me moiety (where X = O, S; Y = O, NH, S). The bond-order between orbitals of pπ symmetry on C1 and Y1 serve...

McDowell, S A
Published in
Journal of computational chemistry

The integrated intensity of vibrational transitions depends on the magnitude of the derivatives of the dipole with respect to nuclear motion. These derivatives are usually obtained by time-consuming ab initio calculations. In this paper we apply a long-range model, based on distributed schemes for describing the charge densities and polarizabilitie...

Zhou, Z Payne, P Vasquez, M Kuhn, N Levitt, M
Published in
Journal of computational chemistry

A new procedure to solve the Poisson-Boltzmann equation is proposed and shown to be efficient. The electrostatic potential due to the reaction field is calculated directly. Self-interactions among the charges are completely eliminated. Therefore, the reference calculation to cancel out the self-energy is not needed. © 1996 by John Wiley & Sons, Inc...

Patchkovskii, S Thiel, W
Published in
Journal of computational chemistry

Analytical second derivatives of the energy are derived and efficiently implemented for semiempirical MNDO-type methods including AM1, PM3, and MNDO/d. A new algorithm for the simultaneous solution of several CPHF equations is proposed in which the amount of memory required is independent of the number of iterations. The analytical approach is fast...

Couty, M Hall, M B
Published in
Journal of computational chemistry

Although the (n + 1)p orbital is unoccupied in transition-metal ground-state configurations which are all nd(x) (n + 1)s(y) , these (n + 1)p functions play a crucial role in the structure of transition metal complexes. As we show here, the usual solution, adding one or more diffuse functions, can be insufficient to create an orbital of the correct ...