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Examines a modified form of Shepard interpolation of ab initio molecular potential energy surfaces. Improvements in accuracy over previous related schemes; Taylor expansion used in the interpolation formula; Parameters determining the confidence volume.

Examines the ab initio potential energy surface for the quartet electronic state of NH[sup +][sub 3] from the collision reaction of N([sup 4]S) and H[sup +][sub 3]. Detailed exploration of the ab initio potential energy surfaces; Analysis on the reaction paths and simulation of reactions; Investigation on the possibility of surface crossing.

Examines the adiabatic potential energy surfaces (PES) for the ground and excited states of triplet methyl cation. Integration of molecular potential energy surfaces with multi-configurational self-consistent field methods; Investigation on the accuracy of PES; Properties of the reaction products.

Collins' method of interpolating a potential energy surface (PES) from quantum chemical calculations for reactive systems (Jordan, M. J. T.; Thompson, K. C.; Collins, M. A. J. Chem. Phys. 1995, 102, 5647. Thompson, K. C.; Jordan, M. J. T.; Collins, M. A. J. Chem. Phys. 1998, 108, 8302. Bettens, R. P. A.; Collins, M. A. J. Chem. Phys. 1999, 111, 816) has been applied to a bound state problem. The interpolation method has been combined for the first time with quantum diffusion Monte Carlo calculations to obtain an accurate ground state zero-point energy, the vibrationally average rotational constants, and the vibrationally averaged internal coordinates. In particular, the system studied was fluoromethane using a composite method approximating the QCISD(T)/6-311++G(2df,2p) level of theory. The approach adopted in this work (a) is fully automated, (b) is fully ab initio, (c) includes all nine nuclear degrees of freedom, (d) requires no assumption of the functional form of the PES, (e) possesses the full symmetry of the system, (f) does not involve fitting any parameters of any kind, and (g) is generally applicable to any system amenable to quantum chemical calculations and Collins' interpolation method. The calculated zero-point energy agrees to within 0.2% of its current best estimate. A[sub 0] and B[sub 0] are within 0.9 and 0.3%, respectively, of experiment. [ABSTRACT FROM AUTHOR]

Interpolated ab initio potential energy surfaces which describe abstraction and exchange reactions in collisions of hydrogen and water are reported. The electronic structure calculations are performed at the QCISD(T) level of theory, with an additivity approximation. A sufficiently large basis set is required to describe the Rydberg character of the electronic state for molecular configurations which are important for the exchange process. Classical and quantum dynamics calculations on the surfaces are presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]