摘要：

A set of permutationally invariant potential energy surfaces for the electronic ground state of formaldehyde is built at several levels of electronic theory and atomic orbital basis sets starting from a database of more than 34,000 ab initio energies. Preliminarily, the reliability of the fitted surfaces is determined by comparing the calculated harmonic frequencies with the corresponding ab initio values. Then, semiclassical estimates of the quantum frequencies of vibration are presented, and their dependence on the employed level of theory, type of atomic orbital basis set, and complexity of the fit is investigated. Comparisons of semiclassical results to experimental data provide a further assessment of the quality of the analytical surfaces and show that anharmonic frequencies are influenced by the precision of the fit, while accurate frequency values are obtained also with density functional theory. Results and conclusions support the use of ab initio "on-the-fly" semiclassical dynamics as a means of spectroscopic investigation when high-level analytical potential energy surfaces are not available.

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