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Based on ab initio data (this is, the optimized geometry, an electronic energy at correlated level and the Hessian matrix), this program can calculate vibrational contributions to internal energy, entropy and heat capacity. A simple scheme for obtaining heats of formation via empirically corrected atomization energies has been implemented that works for silicon hydride compounds only, but the rest of the program is rather general.
Although several anharmonic cases are supported, the majority of calculations uses but two of them: Internal rotation (hindered rotor) and double well oscillation (double minimum oscillator). Anharmonic contributions are calculated using quantum-corrected classical partition functions (Pitzer-Gwinn-correction). The important point is that the program tries to calculate all relevant potential parameters (periodicities, barrier heights, symmetry numbers) automatically, using heuristic algorithms that rely on geometry and hessian matrix alone.
The program has been equipped with a web interface, and can be tested online with a collection of about 200 silicon hydride compounds. The user can influence the way how anharmonic corrections are calculated. If you want to try the program, click here for Anharmonic Thermochemistry. You will also find more information on the method there.
A paper describing the method in short (not the implementation) and exploring the influence of anharmonic corrections for ther high-temperature chemistry of silicon hydrides has appeared in JPC A; a more technical paper that describes the method in detail has been submitted to JCC and is currently in the review phase. A paper on a simple method to treat asymmetric internal rotation appeared in Chem. Phys. Lett..
Furthermore, I have recently published a paper about pseudorotation in JCP. In this paper, I present a simple method to evaluate the frequency of pseudorotation (corresponding to the pseudorotational constant) both for traditional pseudorotation cases (like cyclopentane) and for dynamic Jahn-Teller cases, like the cyclopentadienyl radical (C5H5) and the benzene cation (C6H6+). The method is based on classical mechanics; it requires ab initio optimized structures along the pseudorotational pathway, which can be obtained by restricted geometry optimization.
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