Potentials and geometry

Yoon BJ, Morokuma K, Davidson ER (1985) Structure of ice Ih. Ab-initio two and three-body water-water potentials and geometry optimization. J Chem Phys 83 1223-1231... 

Solomon, E. L, Penfield, K. W., Gewirth, A. A., Lowery, M. D., Shadle, S. E., Guckert, J. A., and LaCroix, L. B. (1996). Electronic structure of the oxidized and reduced blue copper sites Contributions to the electron transfer pathway, reduction potential, and geometry. Inorg. Chim. Acta 243, 67-78. 

Potentials and Geometry. We will describe results for films containing linear short-chain molecules. These are modeled using a simple bead-spring potential that has been used extensively in studies of polymer structure and dynamics (24). Each spherical monomer within the molecule interacts with all other monomers through a Lennard-Jones (LJ) potential Vy that is truncated beyond rc. For monomers separated by a distance r[Pg.92]

Determination of the paiameters entering the model Hamiltonian for handling the R-T effect (quadratic force constant for the mean potential and the Renner paiameters) was carried out by fitting special forms of the functions [Eqs. (75) and (77)], as described above, and using not more than 10 electronic energies for each of the X H component states, computed at cis- and toans-planai geometries. This procedure led to the above mentioned six parameters... 

The electron alfinity and ionization potential can be either for vertical excitations or adiabatic excitations. For adiabatic potentials, the geometry of both ions is optimized. For vertical transitions, both energies are computed for the same geometry, optimized for the starting state. 

Heats of formation, molecular geometries, ionization potentials and dipole moments are calculated by the MNDO method for a large number of molecules. The MNDO results are compared with the corresponding MINDO/3 results on a statistical basis. For the properties investigated, the mean absolute errors in MNDO are uniformly smaller than those in MINDO/3 by a factor of about 2. Major improvements of MNDO over MINDO/3 are found for the heats of formation of unsaturated systems and molecules with NN bonds, for bond angles, for higher ionization potentials, and for dipole moments of compounds with heteroatoms. 

Figure 15. Calculated potential energy surface and geometries of intermediates of the V" + CO2 reaction. The energy of the lowest energy state for the quintet (solid hnes) and triplet (dotted lines) stationary points are shown. Energies are calculated at the CCSD(T)/6-311+G(3df) level, at the B3LYP/6-311+G(d) geometry and include zero-point energy at the B3LYP/6-311+G(d) level.

Figure 1. Schematic of the radial cuts of the ground- and excited-state potential energy surfaces at the linear and T-shaped orientations. Transitions of the ground-state, T-shaped complexes access the lowest lying, bound intermolecular level in the excited-state potential also with a rigid T-shaped geometry. Transitions of the linear conformer were previously believed to access the purely repulsive region of the excited-state potential and would thus give rise to a continuum signal. The results reviewed here indicate that transitions of the linear conformer can access bound excited-state levels with intermolecular vibrational excitation.

Although FEP is mostly useful for binding type of simulations rather than chemical reactions, it can be valuable for reduction potential and pKa calculations, which are of interest from many perspectives. For example, prediction of reliable pKa values of key groups can be used as a criterion for establishing a reliable microscopic model for complex systems. Technically, FEP calculation with QM/MM potentials is complicated by the fact that QM potentials are non-seperable [78], When the species subject to perturbation (A B) differ mainly in electronic structure but similar in nuclear connectivity (e.g., an oxidation-reduction pair), we find it is beneficial to use the same set of nuclear geometry for the two states [78], i.e., the coupling potential function has the form,... 

X-ray structural studies of the diamagnetic anion (406) confirm that the Ir(-I) center is in a distorted coordination geometry intermediate between square planar and tetrahedral, with the P donor atoms in a cis position. The metal-ligand bond distances do not show significant changes among (404), (405), and (406). The Ir1/0 and Ir0/(-1) redox couples are measured at easily accessible potentials and are solvent dependent. 

A few thioether-ligated copper(II) complexes have been reported, however (cf. Section 6.6.3.1.2) (417) (essentially square planar), (418) (two crystalline forms one TBP and other SP),361 (419) (SP),362 (420) (SP),362 (421) (TBP),362 (422) (SP),363 (423) (SP),363 (424) (two independent complexes SP and octahedral),364 (425) (TBP).364 In the complexes (420) and (421), EPR spectra revealed that the interaction between the unpaired electron and the nuclear spin of the halogen atom is dependent on the character of the ligand present. For (424) and (425), spectral and redox properties were also investigated. Rorabacher et al.365 nicely demonstrated the influence of coordination geometry upon CV/Cu1 redox potentials, and reported structures of complexes (426) and (427). Both the Cu1 (Section 6.6.4.5.1) and Cu11 complexes have virtual C3v symmetry. 

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