Journal of Molecular Structure-theochem 

About: Journal of Molecular Structure-theochem is an academic journal. The journal publishes majorly in the area(s): Ab initio & Density functional theory. It has an ISSN identifier of 0166-1280. Over the lifetime, 11609 publications have been published receiving 164465 citations.

The IEF version of the PCM solvation method: an overview of a new method addressed to study molecular solutes at the QM ab initio level

Abstract: The integral equation formalism (IEF) is a recent method (the grounds have been elaborated at the beginning of 1997) addressed to solve the electrostatic solvation problem at the QM level with the aid of apparent surface charges (ASC). IEF uses a new formalism of this problem, based on integral operators never used before in the chemical community and it manages to treat on the same footing linear isotropic solvent models, as well as anisotropic liquid crystals and ionic solutions. In this overview we emphasize the good performances of IEF at the lowest level of its potentialities, i.e. for isotropic solvents, as a new approach to compute solvation free energies and properties (dipole hyperpolarizabilities) of molecular solutes, as well as energy gradients for geometry optimization procedures. Finally we present a new IEF implementation of the nonequilibrium problem for electronic spectra which appears to be decidedly competitive with the previous more standard ASC formulations.

Analysis of the geometry of the hydroxymethyl radical by the “different hybrids for different spins” natural bond orbital procedure

Abstract: We have carried out ab initio UHF/6-31G* calculations on the hydroxymethyl radical, CH 2 OH, and have found the equilibrium structure to be nearly planar with barriers to internal rotation occurring at staggered and eclipsed geometries, in good agreement with experiment. The electronic structure of the radical was analyzed via the “different hybrids for different spins” natural bond orbital (DHDS NBO) procedure, which finds separate Lewis structures for each of the spin systems. The α spin Lewis structure resembles that of the anion; the β spin Lewis structure resembles the corresponding cation. This simple picture, in conjunction with Bent's rule, allows one to understand the principal electronic factors which dictate the structure of the radical CH 2 group and its torsional and inversion potentials. Charge transfer between oxygen non-bonding orbitals and the empty radical orbital in the β spin system is the dominant interaction determining the torsional potential. Smaller hyperconjugative interactions in the α spin system resemble interactions in closed-shell molecules and directly oppose the effect of radical hyperconjugation, thus illustrating the central idea that open-shell potential energy features result from competition between the two different spin systems.

A new oniom implementation in gaussian98. part i. the calculation of energies, gradients, vibrational frequencies and electric field derivatives

Abstract: The IMOMM, IMOMO, and ONIOM methods have been proven to be powerful tools for the theoretical treatment of large molecular systems where different levels of theory are applied to different parts of a molecule. Within this framework we present a modified handling of the link atoms which are introduced to terminate the dangling bonds of the model system. Using this new scheme the definition of the combined energy gradient, the Hessian matrix, and the integration of higher derivatives of the energy with respect to nuclear coordinates and the electric field vector becomes straightforward. This allows for the first time the consistent combination of vibrational frequencies and the calculation of other molecular properties such as IR intensities, Raman intensities as well as dipole moments, polarizabilities, and hyperpolarizabilities. Test calculations for some typical as well as unusual examples and partitioning schemes are presented to demonstrate the power and limitations of the method and to provide guidelines for its applicability. Users of the method are strongly advised to test, calibrate and confirm for themselves the validity of the method combination and the model subsystem for the properties they want to calculate.