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Computational Chemistry & Nanostructures

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Home arrow Research Projects arrow Research projects arrow Efficient determination of vibrational spectra

Efficient determination of vibrational spectra PDF Print E-mail

Experimental infrared studies of biological molecules in condensed phase performed in recent years have increasingly relied on theoretical computations to help interpret the data obtained. This interplay between theory and experiement does not only occur in biological sciences but also increasingly in nano-sciences and thus demonstrates the need for a reliable theoretical method for predicting the spectra of large polyatomic molecules in various environments. In particular, this method has to provide results that are of sufficient accuracy to allow a precise understanding of spectroscopic observations.

ImageIn our research group, we aim to develop a new method that can deal with the vibrational dynamics of large systems, for example molecules on surfaces, solvated systems or biopolymer chains. To achieve this goal, we are curently  implementing a method that focuses on the calculation of the relevant potential energy surface and combined with an efficient solution of the nuclear Schrodinger equation.

Our technique relies on the observations that the potential energy surface (PES) used to perform high-quality vibrational self-consistent field calculations can be "optimised" to include only the parts of the PES that really contribute to the vibrational dynamics of the system. Such reduced PES is then computed using ab initio theory at a fraction of the computational cost of the full PES, thus leading to large speed improvement of the whole vibrational computation.

We have recently implemented an incarnation of this concept – the Fast-VSCF method – which provides an accurate yet fast description of the vibrational spectrum of a given molecular system. This method, which is oulined in a paper (Journal of Chemical Physics, 120 (2004) 562-573), was incorporated to our local version of the GAMESS ab initio program and allows us to compute vibrational spectra up to 50% faster than using the standard direct-VSCF method implemented in GAMESS.

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