Given the high demand for accuracy and accumulated power of theories, extrapolation from matters of fact attract immediate atention. Two cases where extrapolation techniques are validated and proven reliable alternatives to the purist way will be examined. The first case refers to the complete basis set (CBS) limit in electronic structure calculations which is known to be secluded, with CBS extrapolation being key due to its simplicity and reliability [1,2]. Aiming at massive calculations and global potentials, we have investigated how CBS extrapolatation from basis sets of the lowest rungs of the hierarchical staircase, namely minimal (M) and even subminimal (sM) as opposed to frequently used extended (E) basis sets, can help on the endeavour. The second hinges on wave packet quantum dynamics (WPQD) where the Fast Fourier Transform method is frequently employed. Since this scales as cNlogN where N is the number of grid points, a huge demand for computational resources [3,4] is obvious. However, the correspondence principle tells that the quantum results should approach their classical counterparts at high energies where the former are most expensive. Because quasiclassical trajectory (QCT) calculations are affordable at arbitray collision energies even for large systems, extrapolation to higher total angular momenta (J) from the affordable WPQD calculations for low J values (e.g., J=0) can be done using classical dynamics as guiding asymptotic theory. Proposed long ago [5], the approach is here revisited using novel results for the H+O2 reaction [4]. Itemized the basic difficulties and ways out, the carbon clusters illustrate the studies ongoing in our Group. With the focal point on global functions for the most relevant electronic states of carbon trimers and tetramers, results for pure carbon clusters up to C10 will be also presented. Hopefully, ongoing dynamics and kinetics results for the reaction C2+C2→C3+C are also reported for the first time. Some closing remarks and prospects for future work end the talk.

Extrapolations in electronic structure and dynamics with global potentials for small carbon clusters at the focal point

256th National Meeting (2018)

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